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CTEMPs OSU-UNR

CTEMPs

Subject Areas: hydrology, distributed temperature sensing, DTS, UAS, hydrogeology

 Recent Activity

ABSTRACT:

Near-surface wind speed is typically only measured by point observations. The so-called Actively Heated Fiber-Optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations, allowing for better understanding of different processes. However, before it can be widely used, its performance needs to be tested in a range of settings. Therefore, in this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind-tunnel setup to assess both the accuracy and the precision of AHFO as well as its potential for outdoor atmospheric operation. The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s time scale. The flow in the wind tunnel is varied in a controlled manner, such that the mean wind, ranges between 1 and 17 m/s. Comparison of the AHFO measurements with observations from a sonic anemometer shows a high overall correlation, ranging from 0.94-0.99. Also, both precision and accuracy are greater than 95 %. As such, it is concluded that the AHFO has potential to be employed as an outdoor observational technique in addition to existing techniques. In particular, it allows for characterization of spatial varying fields of mean wind in complex terrain, such as in canopy flows or in sloping terrain. In the future the technique could be combined with regular Distributed Temperature Sensing (DTS) for turbulent heat flux estimation in micrometeorological/hydrological applications.

Raw DTS project data will be available in 2020 by contacting ctemps@unr.edu.

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ABSTRACT:

Goal: Develop techniques for observing 3D, high resolution atmospheric motions during stably stratified
conditions.
Missing Physics: The need for a full 3D sensor
1) Fundamental mismatch between scales of variability in wind and temperature break observation assumptions
2) Stability and wind speed alone can not describe the strength of mixing during weak wind conditions
3) Spatial heterogeneity in both temperature and wind fields at varying scales

Raw DTS project data will be available in 2020 from ctemps@unr.edu

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ABSTRACT:

The large internal seiche of the Lucerne Basin of Lake Chelan was described in Pelletier et al., 1989, in short, the rocking back and forth of the deep cold water in the Lucerne Basin. The data for this study was collected in 1986 and 1987 and showed an extreme internal seiche. During the summer of 1987 the amplitude of the rocking of the deep cold water was as much as 70 m and the period was approximately 3 days. The main goals of this study were to a) investigate the internal seiche in more detail than was possible in the 1980’s and b) determine how the seiche interacted with the sill between the Lucerne Basin and the Wapato Basin.

This study is significant to water quality of Lake Chelan in two ways. 1) Without knowing the status of the internal seiche under summer conditions, it is difficult to know the source of waters being sampled, the deep cold water versus the shallow warm water in the lake. Each of these waters typically exhibit different water quality signatures. 2) The interaction of the internal seiche with the lake bottom likely influences the transport of fine sediment, sediment distribution and water clarity in the vicinity of the narrows of Lake Chelan. Without knowledge of the seiche dynamics it will be difficult to interpret secchi depths and related water quality parameters in this part of the lake.

Raw project data will be available in 2020 by contacting ctemps@unr.edu

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ABSTRACT:

Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that MO similarity is not applicable in the SBL due to the non-homogeneous, non-stationary flow, no universal organizing theory for the surface SBL has been presented. This poses a problem when examining aerosol movement as a function of atmospheric dynamics. It is known that stable air stratification results in katabatic downslope winds, even in very shallow topographic airsheds. These downslope winds can converge with background flow, and it is hypothesized that this convergence provides a starting point for specific events, such as internal gravity waves. Even though the stable boundary layer is normally shallow, internal gravity waves can propagate at an angle from the horizontal plane, and modify local shear, thus generating periodic turbulent mixing in space. Some studies have measured converging background and drainage flows in mountain areas, however, few studies have examined this in less dramatic, but more common, topographic areas. We are conducting a measurement campaign to address these open issues.

Raw DTS project data will be available in 2020 by contacting ctemps@unr.edu

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ABSTRACT:

The use of tile drainage is documented as far back as 200 B. C. and continues to be used in poorly drained agricultural regions throughout the world. Recent increases in annual precipitation throughout the mid-western United States, the potential for future regulation of tile, and more efficient installation methods for plastic tile have accelerated tile installation across the region. While good for crop production, the eco-hydrologic impacts of this modification have been shown to adversely affect natural drainage networks. Knowing the location of tile drain networks is essential to developing groundwater and surface water models. The geometry of tile networks installed decades ago has often been lost with time or was never well documented in the first place. Previous work has recognized that tiles can be observed for certain soil types in visible remote sensing data due to changes in soil albedo. The soil surface directly above the tile appears to have a lower soil moisture content due to strong water table gradients adjacent to tiles, causing a detectable color contrast at the surface. In this work, small Unmanned Aerial Systems (sUAS) were used to collect high resolution visible and thermal data to map tile drain patterns. Within less than 96 hours of a 12 mm rain event, a total of approximately 60 hectares of sUAS thermal and RGB data were acquired at two different locations at the Intensively Managed Lands Critical Zone Observatory in Illinois. Selected thermal images were co-registered with RGB images at known tile locations. The thermal imagery showed limited evidence of thermal contrast related to the tile, however, it is possible that a contrast could have been detected sooner after the rain event when greater thermal contrasts due to lower soil moisture proximal to tile would be expected. The RGB data, however, elucidated the tile entirely at one site and provided traces of the tile at the other site. These results illustrate the importance of the timing of sUAS data collection with respect to the precipitation event. Ongoing related work focusing on laboratory and numerical experiments to better quantify feedbacks between albedo, soil moisture, and heat transfer will help predict the optimal timing of data collection for applications such as tile mapping.

Raw project data is available by contacting ctemps@unr.edu

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Ofu Island, American Samoa, DTS Survey
Created: Sept. 1, 2017, 4:57 p.m.
Authors: Reid, Emma · Davis, Kristen

ABSTRACT:

The effects of climate change on corals are not uniform. Some corals tolerate greater rises in temperature, even across an individual reef and others thrive in naturally acidified waters. This phenomenon is present on Ofu Island, in American Samoa, where we conducted a field experiment. Identifying these resilient corals and prioritizing their protection may be the best strategy for long-term conservation of coral ecosystems. Although it is not fully understood what makes certain reefs more resilient to coral bleaching than others, emerging evidence suggests that reefs living in areas with naturally variable thermal environments may have higher temperature tolerance. By deploying DTS technology in the back-reef of Ofu Island, we can produce maps of environmental heterogeneity of unprecedented spatiotemporal resolution.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

This multi-year project assess landscape and stream responses to the installation of a beaver dam analogue in a western US stream. We will use UAS data to collect data on the stream and surrounding landscape before the beaver dam analogue is installed, and perform a post-installation assessment of localized changes. Our goal is to better understand how beaver dam analogues may alter landscape resilience in terms of sustaining connections between groundwater and surface water systems.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Groundwater-surface water (GW-SW) flux measurement techniques, such as reach mass-balance, seepage meters, Darcian flux and temperature sensing can be applied simultaneously to provide multiple lines of evidence (e.g., Gonzalez et al. 2015, Schmadel et al. 2014, Kennedy et al. 2009, Gilmore et al. 2016b), but challenges remain for directly linking results from different spatial and temporal scales of measurement. For smaller streams where groundwater discharge is a significant percentage of stream discharge into the reach (typically ≥10%), the integrated groundwater flux from point measurements can be compared to a larger-scale (i.e. 10^2-10^3 m reach length) approach to confirm results. But for reaches in larger stream (river) systems, the stream-groundwater discharge ratio is usually much too large to use reach mass balance as a direct point of comparison (Gilmore et al. 2016b, Schmadel et al. 2010, Jain, 2000). A promising approach for linking point measurements and testing interpolation techniques in large river systems is fiber-optic distributed temperature sensing (FO-DTS) (Briggs et al. 2012a, Briggs et al. 2012b, Tyler et al. 2009). FO-DTS uses a fiber-optic cable to detect groundwater discharge through the streambed along the length of the cable (typically ≤1km). This may be an effective way to “connect the dots” between point measurements of groundwater discharge in large systems (Krause et al. 2012), when other techniques like reach mass balance, are not feasible. The overall goal of this research is to develop an optimal approach to link point measurements of groundwater-surface water fluxes in large river systems. The specific objectives are to: (1) test the combined DTS and point-measurement approach in a small stream, where interpolated results can be confirmed using a reach mass-balance approach, and (2) apply the technique in larger river systems to characterize spatial distributions and temporal variability of groundwater fluxes at existing groundwater-surface water monitoring stations on larger rivers. This project will improve techniques for multi-scale measurement of groundwater-surface water interactions, give critical insight into temporal and spatial variability of water fluxes in larger river systems, and improve our understanding of the value of existing groundwater-surface water monitoring stations.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Surface and groundwater discharges and contaminant fluxes can vary with time and space depending upon the hydrogeological processes and geological setting of the area of interest. This study examined a ~300-m-long, channelized reach of a first-order perennial stream, Little Bayou Creek, in the Coastal Plain of far western Kentucky during the period October 2010–February 2012. Along the study reach, springs discharge groundwater contaminated by the chlorinated organic compound trichloroethene (TCE) and radionuclide technetium-99 (99Tc) released as a result of past activities at the U.S. Department of Energy’s Paducah Gaseous Diffusion Plant. The study addressed variability in groundwater discharge patterns and contaminant concentrations at various timescales (seasonal, annual, and decadal) and the extent to which the discharge sites are spatially persistent. Understanding patterns of groundwater discharge along a stream can be important for assessing the fate and transport of aqueous contaminants.

Groundwater discharge was estimated during baseflow conditions using different mass-balance approaches, including velocity-area and dye-dilution gauging. Discharge fluctuated seasonally but typically increased downstream, indicating the entire study reach to be gaining throughout the year. Discharge rates of individual springs also fluctuated seasonally. Tracer test data were utilized to model flow and transient storage along the reach using the USGS software OTIS-P. Cross-sectional area determined from OTIS-P was similar to that measured by velocity-area gauging. Reach area-normalized discharge fluxes were comparable to values determined by Darcy’s law calculations from a pair of monitoring wells at the downstream end of the study reach. Temperature data acquired from probing along grids in winter and summer, from fiber-optic sensing along the reach in autumn, and from data-loggers and manual measurements in springs were used to delineate focused discharge locations. Comparison of temperature-probing results with prior studies indicated that locations of some springs persisted over a decade, whereas other springs emerged and disappeared. Because the stream is located in unlithified sediments, discharge rates of springs appear to fluctuate with soil piping and collapse along joints in fractured clay. Contaminant concentrations in springs decreased downstream along the reach and were lower than observed during September 1999 – May 2001. The continued occurrence of dissolved oxygen and the absence of TCE daughter products in springs suggest that the decrease in TCE concentrations resulted from the installation of upgradient extraction wells, rather than from intrinsic reductive degradation.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Recent research has demonstrated the use of in-well heat tracer tests monitored by a fiber optic distributed temperature sensing (DTS) system to characterize borehole flow conditions in open bedrock boreholes. However, the accuracy of borehole flow rates determined from in-well heat tracer tests has not been evaluated. The purpose of the research presented here is to determine whether borehole flow rates obtained using DTS-monitored in-well heat tracer tests are reasonable, and to evaluate the range of flow rates measureable with this method. To accomplish this, borehole flow rates measured using in-well heat tracer tests are compared to borehole flow rates measured in the same boreholes using an impeller or heat pulse flowmeter. A comparison of flow rates measured using in-well heat tracer tests to flow rates measured with an impeller flowmeter under the same conditions showed good agreement. A comparison of in-well heat tracer test flow rate measurements to previously-collected heat pulse flowmeter measurements indicates that the heat tracer test results produced borehole flow rates and flow profiles similar to those measured with the heat pulse flowmeter. The results of this study indicate that borehole flow rates determined from DTS-monitored in-well heat tracer tests are reasonable estimates of actual borehole flow rates. In addition, the range of borehole flow rates measurable by in-well heat tracer tests spans from less than 10−1 m/min to approximately 101 m/min, overlapping the ranges typically measurable with an impeller flowmeter or a heat pulse flowmeter, making in-well heat tracer testing a versatile boreholeflow logging tool.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Circulation patterns over the inner continental shelf are spatially complex and highly variable in time. Significant fluxes of water, heat and other tracers may be associated with alongshore variability, especially in regions where the coastline and isobaths are not straight. Under stratified conditions, sustained subsurface observations are needed to characterize three-dimensional patterns of circulation, even in shallow water. To observe multiple scales of alongshore variability, a distributed temperature sensing system (DTS) was deployed within a larger-scale mooring array south of Martha's Vineyard, MA. A fiber-optic cable oriented in the alongshore direction was used to collect bottom temperature measurements with 5 m horizontal resolution, over a distance of 4.9 km. Although temperature gradients are generally stronger in the cross-shelf direction, significant variability is observed in the along-shelf direction. Along the 15 m isobath, rapid cooling events are observed with greater regularity and magnitude at locations closer to irregular bathymetry. The DTS observations show that fronts travel away from this region of strong tidal and bathymetric variability with an alongshore component. Lack of uniformity in magnitude and frequency of cooling events, at sites separated by less than 5 km in the alongshore direction, indicates that alongshore differences are present at short time scales of less than a day. Thus, the characteristics of high-frequency temperature variability at one location are therefore not necessarily representative of other nearby locations along the same isobath.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

This study demonstrated a new method for mapping high-resolution (spatial: 1 m, and temporal: 1 h) soil moisture by assimilating distributed temperature sensing (DTS) observed soil temperatures at intermediate scales. In order to provide robust soil moisture and property estimates, we first proposed an adaptive particle batch smoother algorithm (APBS). In the APBS, a tuning factor, which can avoid severe particle weight degeneration, is automatically determined by maximizing the reliability of the soil temperature estimates of each batch window. A multiple truth synthetic test was used to demonstrate the APBS can robustly estimate soil moisture and properties using observed soil temperatures at two shallow depths. The APBS algorithm was then applied to DTS data along a 71 m transect, yielding an hourly soil moisture map with meter resolution. Results show the APBS can draw the prior guessed soil hydraulic and thermal properties significantly closer to the field measured reference values. The improved soil properties in turn remove the soil moisture biases between the prior guessed and reference soil moisture, which was particularly noticeable at depth above 20 cm. This high-resolution soil moisture map demonstrates the potential of characterizing soil moisture temporal and spatial variability and reflects patterns consistent with previous studies conducted using intensive point scale soil moisture samples. The intermediate scale high spatial resolution soil moisture information derived from the DTS may facilitate remote sensing soil moisture product calibration and validation. In addition, the APBS algorithm proposed in this study would also be applicable to general hydrological data assimilation problems for robust model state and parameter estimation.

Raw project data is available by contacting ctemps@unr.edu

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Distributed Temperature Sensors Deployed in WyCEHG Focus Sites
Created: Nov. 30, 2017, 10:12 p.m.
Authors: Andrew Parsekian

ABSTRACT:

This summer we deployed a fiber-optic temperature monitoring technology called Distributed Temperature Sensor (DTS) in the No-Name drainage in the Medicine Bow National Forest. DTS works on the principle that the optical properties of telecommunication-grade glass fiber cables vary with temperature. A laser sends light pulses down a protected fiber and a sensor records any changes in the character of the light pulse, then back calculates temperature at every meter along the fiber, which can be several kilometers long. This provides very high spatial resolution, unmatched by other environmental temperature sensing technologies. This stream Influxes of groundwater to the channel are identified where abrupt changes in temperature are revealed; temperature changes in the channel due to atmospheric induced warming and cooling occur gradually along the DTS system. This system can identify gains that may occur via return flow or subsurface lateral flow. Over the summer, we deployed a DTS leased from Center for Transformative Environmental Monitoring Programs (CTEMPS) in two of WyCEHG’s high-intensity study sites. In the No-Name Creek Watershed, the DTS was deployed on a steeply sloped 550 m reach of stream to look for temperature signals that indicate exchange between the surface water and groundwater. This watershed is severely effected by trees that have succumbed to the pine bark beetle, and therefore it was an arduous deployment requiring many WyCEHG volunteers to navigate the many fallen logs that crossed the stream. Once set up, the autonomous DTS system collected data every ten minutes for 16 days without a hitch. The rich temporal and spatial temperature data we collected allows us to identify zones of groundwater exchange, and investigate the stream’s response to solar radiation and the ambient environment. A second reach of stream –the Blair tributary – was also instrument with DTS to measure inflow along the channel through interpretation of small changes in bed temperature. The Blair tributary has a much shallower slope than No-Name, and it not affected by deadfall. Installation was much more straightforward, however a new challenge arose: beavers found and damaged the cables during measurement. Although the DTS instrument required quite a bit of work by many people to install, this turned out to be great benefit. We were able to involve many “volunteer” WyCEHGers including graduate students from a variety of disciplines and several Summer Research Assistantship Program (SRAP) pre-college students that were doing research apprenticeships over the summer. This was a valuable opportunity to expose students to the hydrogeophysics research that is fundamental to WyCEHGs mission and excite the next generation of scientists with hands-on field experiences.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The question: ‘how does a streambed change over a minor flood?’ does not have a clear answer due to lack of measurement methods during high flows. We investigate bedload transport and disentrainment during a 1.5-year flood by linking field measurements using fiber optic distributed temperature sensing (DTS) cable with sediment transport theory and an existing explicit analytical solution to predict depth of sediment deposition from amplitude and phase changes of the diurnal near-bed pore-water temperature. The method facilitates the study of gravel transport by using near-bed temperature time series to estimate rates of sediment deposition continuously over the duration of a high flow event coinciding with bar formation. The observations indicate that all gravel and cobble particles present were transported along the riffle at a relatively low Shields Number for the median particle size, and were re-deposited on the lee side of the bar at rates that varied over time during a constant flow. Approximately 1–6% of the bed was predicted to be mobile during the 1.5-year flood, indicating that large inactive regions of the bed, particularly between riffles, persist between years despite field observations of narrow zones of local transport and bar growth on the order ~3–5 times the median particle size. In contrast, during a seven-year flood approximately 8–55% of the bed was predicted to become mobile, indicating that the continuous along-stream mobility required to mobilize coarse gravel through long pools and downstream to the next riffle is infrequent. Copyright © 2017 John Wiley & Sons, Ltd.

Raw project data is available by contacting ctemps@unr.edu

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Dynamics and global relevance of fumarolic ice caves on Erebus Volcano, Antarctica.
Created: Dec. 29, 2017, 9:07 p.m.
Authors: Aaron Curtis

ABSTRACT:

This dissertation seeks to characterize the cave atmospheres and dynamics of fumarolic ice caves. The introduction presents a broad framework for understanding the caves and describes the historical and conservation context into which the work fits. This framework provides the motivation for five investigations which are presented as Chapters 2 through 6. Chapter 2 details a fiber-optic distributed temperature sensing (FODTS) experiment in which 438m of fiber-optic cable was deployed along the main passages of Warren Cave on Erebus Volcano, Antarctica. Point sources of warm gas flowing into the cave manifested as multi-degree C temperature anomalies and persisted throughout the weeklong experiment. Observed temperatures were anti-correlated with local atmospheric pressure, indicating barometric pumping of the gas vents. Chapter 3 extends the FODTS technique used in Chapter 2 to three dimensions for volumetric imaging of the temperature field inside a fumarolic ice cave chamber. Using terrestrial laser scanning (TLS) and automatic pointcloud classification techniques, I precisely located each virtual temperature sensor along the fiber optic cable. Interpolation and analysis of spatial patterns revealed a strong, upward-positive temperature gradient which averaged 0.265C m-1 over the 7 day experiment. I used satellite data and a permafrost model to assess potential Holocene volcano ice interaction globally, finding that 19.8% of known Holocene volcanic centers host glaciers or areas of permanent snow. The results, presented in Chapter 4, suggest that fumarolic ice caves are globally widespread and largely undiscovered. Fumarolic ice caves are expected to form when degassing begins beneath any volcano with moderate ice overburden. In Chapter 5, I present six years of morphological observations using TLS, structure from motion (SfM), and traditional cave survey, revealing that fumarolic ice caves change on the scale of tens of centimeters annually, and that the topography above the caves responds to enlargement of chambers through melting. I find that the cave wall icehas passed the pore-closeoff density, and conclude that densification is accelerated by heat from the cave. The rapid passage enlargement observed means that fresh rock substrate regularly becomes available to the cave microbial communities. For theoretical context, I developed two “toy” models. A computational fluid dynamics (CFD) simulation of cave melt is presented which represents a cave during initiation of growth.A simple flow model based on Glen's flow law, gives a first estimate of expected passage closure rates due to ice creep. Chapter 6 represents a collaborative effort to characterize the isotopic and chemical composition (δ2H and δ18O) of Erebus' snow and ice mantle which hosts the fumarolic ice caves. We found that snow samples from the entire summit caldera area, including ice cores collected through fumarolic ice tower walls, fall far outside an Antarctic Meteoric Water Field which encompasses all other available Antarctic snow isotope data. This suggests a magmatic component in the snow, which may be supplied by the plume emanating from Erebus' main crater. Several cross-cutting themes are addressed in multiple chapters. I discuss how fumarolic ice caves provide important indicators of volcanic unrest, analogues of extraterrestrial systems, and critical habitats for microbes. Going forward, this dissertation should be a foundation on which to plan the further exploration of fumarolic ice caves on Earth and elsewhere in the solar system. Keywords: distributed temperature sensing, LiDAR, isotopes, glaciovolcanism, flank degassing, Erebus, Antarctica.

Raw project data is available by contacting ctemps@unr.edu

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Characterizing Heterogeneity in Infiltration Rates During Managed Aquifer Recharge
Created: Dec. 29, 2017, 9:43 p.m.
Authors: Chloe Mawer

ABSTRACT:

Infiltration rate is the key parameter that describes how water moves from the surface into a groundwater aquifer during managed aquifer recharge (MAR). Characterization of infiltration rate heterogeneity in space and time is valuable information for MAR system operation. In this study, we utilized fiber optic distributed temperature sensing (FO-DTS) observations and the phase shift of the diurnal temperature signal between two vertically co-located fiber optic cables to characterize infiltration rate spatially and temporally in a MAR basin. The FO-DTS measurements revealed spatial heterogeneity of infiltration rate: approximately 78% of the recharge water infiltrated through 50% of the pond bottom on average. We also introduced a metric for quantifying how the infiltration rate in a recharge pond changes over time, which enables FO-DTS to be used as a method for monitoring MAR and informing maintenance decisions. By monitoring this metric, we found high-spatial variability in how rapidly infiltration rate changed during the test period. We attributed this variability to biological pore clogging and found a relationship between high initial infiltration rate and the most rapid pore clogging. We found a strong relationship (R2 =0.8) between observed maximum infiltration rates and electrical resistivity measurements from electrical resistivity tomography data taken in the same basin when dry. This result shows that the combined acquisition of DTS and ERT data can improve the design and operation of a MAR pond significantly by providing the critical information needed about spatial variability in parameters controlling infiltration rates.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The cost effective maintenance of underwater pressure pipes for sewage disposal in Austria requires the detection and localization of leakages. Extrusion of wastewater in lakes can heavily influence the water and bathing quality of surrounding waters. The Distributed Temperature Sensing (DTS) technology is a widely used technique for oil and gas pipeline leakage detection. While in pipeline leakage detection, fiber optic cables are installed permanently at the outside or within the protective sheathing of the pipe; this paper aims at testing the feasibility of detecting leakages with temporary introduced fiber optic cable inside the pipe. The detection and localization were tested in a laboratory experiment. The intrusion of water from leakages into the pipe, producing a local temperature drop, served as indicator for leakages. Measurements were taken under varying measurement conditions, including the number of leakages as well as the positioning of the fiber optic cable. Experiments showed that leakages could be detected accurately with the proposed methodology, when measuring resolution, temperature gradient and measurement time were properly selected. Despite the successful application of DTS for leakage detection in this lab environment, challenges in real system applications may arise from temperature gradients within the pipe system over longer distances and the placement of the cable into the real pipe system.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

In recent years, the spatial resolution of fiber-optic distributed temperature sensing (DTS) has been enhanced in various studies by helically coiling the fiber around a support structure. While solid polyvinyl chloride tubes are an appropriate support structure under water, they can produce considerable errors in aerial deployments due to the radiative heating or cooling. We used meshed reinforcing fabric as a novel support structure to measure high-resolution vertical temperature profiles with a height of several meters above a meadow and within and above a small lake. This study aimed at quantifying the radiation error for the coiled DTS system and the contribution caused by the novel support structure via heat conduction. A quantitative and comprehensive energy balance model is proposed and tested, which includes the shortwave radiative, longwave radiative, convective, and conductive heat transfers and allows for modeling fiber temperatures as well as quantifying the radiation error. The sensitivity of the energy balance model to the conduction error caused by the reinforcing fabric is discussed in terms of its albedo, emissivity, and thermal conductivity. Modeled radiation errors amounted to −1.0 and 1.3 K at 2 m height but ranged up to 2.8 K for very high incoming shortwave radiation (1000 J s−1 m−2) and very weak winds (0.1 m s−1). After correcting for the radiation error by means of the presented energy balance, the root mean square error between DTS and reference air temperatures from an aspirated resistance thermometer or an ultrasonic anemometer was 0.42 and 0.26 K above the meadow and the lake, respectively. Conduction between reinforcing fabric and fiber cable had a small effect on fiber temperatures (< 0.18 K). Only for locations where the plastic rings that supported the reinforcing fabric touched the fiber-optic cable were significant temperature artifacts of up to 2.5 K observed. Overall, the reinforcing fabric offers several advantages over conventional support structures published to date in the literature as it minimizes both radiation and conduction errors.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Taylors' frozen turbulence hypothesis suggests that all turbulent eddies are advected by the mean streamwise velocity, without changes in their properties. This hypothesis has been widely invoked to compute Reynolds averaging using temporal turbulence data measured at a single point in space. However, in the atmospheric surface layer, the exact relationship between convection velocity and wave number k has not been fully revealed since previous observations were limited by either their spatial resolution or by the sampling length. Using Distributed Temperature Sensing (DTS), acquiring turbulent temperature fluctuations at high temporal and spatial frequencies, we computed convection velocities across wave numbers using a phase spectrum method. We found that convection velocity decreases as k−1/3 at the higher wave numbers of the inertial subrange instead of being independent of wave number as suggested by Taylor's hypothesis. We further corroborated this result using large eddy simulations. Applying Taylor's hypothesis thus systematically underestimates turbulent spectrum in the inertial subrange. A correction is proposed for point-based eddy-covariance measurements, which can improve surface energy budget closure and estimates of CO2 fluxes.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The need to identify groundwater seepage locations is of great importance for managing both stream water quality and groundwater sourced ecosystems due to their dependency on groundwater-borne nutrients and temperatures. Although several reconnaissance methods using temperature as tracer exist, these are subjected to limitations related to mainly the spatial and temporal resolution and/or mixing of groundwater and surface water leading to dilution of the temperature differences. Further, some methods, for example, thermal imagery and fiber optic distributed temperature sensing, although relative efficient in detecting temperature differences over larger distances, these are labor-intensive and costly. Therefore, there is a need for additional cost-effective methods identifying substantial groundwater seepage locations. We present a method expanding the linear regression of air and stream temperatures by measuring the temperatures in dual-depth; in the stream column and at the streambed-water interface (SWI). By doing so, we apply metrics from linear regression analysis of temperatures between air/stream and air/SWI (linear regression slope, intercept, and coefficient of determination), and the daily water temperature cycle (daily mean temperatures, temperature variance, and the mean diel temperature fluctuation). We show that using metrics from only single-depth stream temperature measurements are insufficient to identify substantial groundwater seepage locations in a head-water stream. Conversely, comparing the metrics from dual-depth temperatures show significant differences; at groundwater seepage locations, temperatures at the SWI merely explain 43–75% of the variation opposed to ⩾ 91% at the corresponding stream column temperatures. In general, at these locations at the SWI, the slopes ( < 0.25) and intercepts ( > 6.5 °C) are substantially lower and higher, respectively, while the mean diel temperature fluctuations ( < 0.98 °C) are decreased compared to remaining locations. The dual-depth approach was applied in a post-glacial fluvial setting, where metrics analyses overall corroborated with field measurements of groundwater fluxes and stream flow accretions. Thus, we propose a method reliably identifying groundwater seepage locations along streambeds in such settings.

Raw project data is available by contacting ctemps@unr.edu

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Downhole Distributed Temperature Sensing in Fractured Rock
Created: Dec. 29, 2017, 10:49 p.m.
Authors: MATT VITALE

ABSTRACT:

Newmont’s Leeville Mine is located on the western side of the Tuscarora Range in northeastern Nevada. A 587 meter geotechnical pilot borehole in silty carbonate was drilled during 2012 prior to excavating a 10 m diameter vent shaft using ground freezing technology. Fiber optic cable was installed in the borehole and backfilled with cement-bentonite grout. In 2013 a distributed temperature interrogator was installed, which measured temperature along the fiber optic cable at 0.25 m and 0.02 °C resolution. After initial data were taken, a lower-resolution interrogator was installed for longer-term data collection, which measures temperature along the fiber optic cable at 1 m and 0.2 °C resolution. The intent was to utilize temperature for aquifer characterization. Daily measurements were programmed and run from December 21, 2013 through June 20, 2015 for a total of 546 daily temperature traces comprising 321,048 data points. Descriptive data analysis is presented, indicating a saturated zone 122 m below ground surface where a rapid temperature decrease of near 2 °C was seen. Similar downhole temperature changes are observed at 367 and 528 m coinciding with fracture flow zones where lateral water flow is suspected. Distinct slope profiles of the local geothermal gradient are evident between the fracture flow zones, indicating separate hydrostratigraphic units. The close-by ground freezing provided a thermal tracer of water movement. Temperature generally decreased over time because of the freeze process. Greater than 7 °C difference was observed in zones interpreted as lower permeability where conductive heat transfer was likely dominant. Advective flow at the 366 and 526 m depths showed substantially less temperature variability. It is at these depths where water flows through fractures at a greater velocity than the bulk rock and where the water temperature is indicative of the greater aquifer system. The smallest temperature change was less than 2 °C at 579 meters depth, which is interpreted to be the upper zone of the semi-saturated Roberts Mountain Thrust Fault.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Multicomponent groundwater tracer tests were conducted in a well-characterized field site in Altona, NY using inert carbon-cored nanoparticles and a thermally degrading phenolic compound. Experiments were conducted in a mesoscale reservoir consisting of a single subhorizontal bedding plane fracture located 7.6 m below ground surface contained between two wells separated by 14.1 m. The reservoir rock, initially at 11.7°C, was heated using 74°C water. During the heating process, a series of tracer tests using thermally degrading tracers were used to characterize the progressive in situ heating of the fracture. Fiber-Optic Distributed Temperature Sensing (FODTS) was used to measure temperature rise orthogonal to the fracture surface at 10 locations. Recovery of the thermally degrading tracer's product was increased as the reservoir was progressively heated indicating that the advancement of the thermal front was proportional to the mass fraction of the thermally degrading tracer recovered. Both GPR imaging and FODTS measurements reveal that flow was reduced to a narrow channel which directly connected the two wells and led to rapid thermal breakthrough. Computational modeling of inert tracer and heat transport in a two-dimensional discrete fracture demonstrate that subsurface characterization using inert tracers alone could not uniquely characterize the Altona field site. However, the inclusion of a thermally degrading tracer may permit accurate subsurface temperature monitoring. At the Altona field site, however, fluid-rock interactions appear to have increased reaction rates relative to laboratory-based measurements made in the absence of rock surfaces.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

We investigate nocturnal flow dynamics and temperature behaviour near the surface of a 170-m long gentle slope in a mid-range mountain valley. In contrast to many existing studies focusing on locations with significant topographic variations, gentle slopes cover a greater spatial extent of the Earth’s surface. Air temperatures were measured using the high-resolution distributed-temperature-sensing method within a two-dimensional fibre-optic array in the lowest metre above the surface. The main objectives are to characterize the spatio-temporal patterns in the near-surface temperature and flow dynamics, and quantify their responses to the microtopography and land cover. For the duration of the experiment, including even clear-sky nights with weak winds and strong radiative forcing, the classical cold-air drainage predicted by theory could not be detected. In contrast, we show that the airflow for the two dominant flow modes originates non-locally. The most abundant flow mode is characterized by vertically-decoupled layers featuring a near-surface flow perpendicular to the slope and strong stable stratification, which contradicts the expectation of a gravity-driven downslope flow of locally produced cold air. Differences in microtopography and land cover clearly affect spatio-temporal temperature perturbations. The second most abundant flow mode is characterized by strong mixing, leading to vertical coupling with airflow directed down the local slope. Here variations of microtopography and land cover lead to negligible near-surface temperature perturbations. We conclude that spatio-temporal temperature perturbations, but not flow dynamics, can be predicted by microtopography, which complicates the prediction of advective-heat components and the existence and dynamics of cold-air pools in gently sloped terrain in the absence of observations.

Raw project data is available by contacting ctemps@unr.edu

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Attenuation of wind-induced pressure perturbations in alpine snow
Created: Dec. 29, 2017, 11:37 p.m.
Authors: STEPHEN A. DRAKE

ABSTRACT:

Windpumping has been identified as a process that could potentially enhance sublimation of surface snow at high forcing frequency and spawn air movement deeper in firn at lower frequencies. We performed an experiment to examine the relationship between high-frequency wind and pressure measurements within the top meter of an alpine snowpack and compared experimental results with two theoretical predictions. We find that both theoretical predictions underestimate high-frequency perturbation pressure attenuation with depth in the near-surface snowpack and the discrepancy between theory and measurement increases with perturbation pressure frequency. The impact of this result for near-surface snow is that potential enhanced sublimation will occur over a shallower snow depth than these two theories predict. Correspondingly, interstitial air mixing at depth in firn will be driven by lower frequencies than these two theories predict. While direct measurement of these energy-rich lower frequencies is beyond the scope of this paper, stationary pressure measurements validate the presence of a pressure field that could drive near-surface circulation.

Raw project data is available by contacting ctemps@unr.edu

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Use of Distributed Temperature Sensing Technology to Characterize Fire Behavior
Created: Dec. 29, 2017, 11:41 p.m.
Authors: Douglas Cram

ABSTRACT:

We evaluated the potential of a fiber optic cable connected to distributed temperature sensing (DTS) technology to withstand wildland fire conditions and quantify fire behavior parameters. We used a custom-made ‘fire cable’ consisting of three optical fibers coated with three different materials—acrylate, copper and polyimide. The 150-m cable was deployed in grasslands and burned in three prescribed fires. The DTS system recorded fire cable output every three seconds and integrated temperatures every 50.6 cm. Results indicated the fire cable was physically capable of withstanding repeated rugged use. Fiber coating materials withstood temperatures up to 422 °C. Changes in fiber attenuation following fire were near zero (−0.81 to 0.12 dB/km) indicating essentially no change in light gain or loss as a function of distance or fire intensity over the length of the fire cable. Results indicated fire cable and DTS technology have potential to quantify fire environment parameters such as heat duration and rate of spread but additional experimentation and analysis are required to determine efficacy and response times. This study adds understanding of DTS and fire cable technology as a potential new method for characterizing fire behavior parameters at greater temporal and spatial scales.

Raw project data is available by contacting ctemps@unr.edu

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Polymictic pool behaviour in a montane meadow, Sierra Nevada, CA
Created: Dec. 29, 2017, 11:45 p.m.
Authors: Ryan Lucas

ABSTRACT:

We observed polymictic behaviour in stream pools in Long Meadow, Sequoia National Park, California—part of the Southern Sierra Critical Zone Observatory. Stream pools stratified thermally during the day time and were isothermal at night—this pattern persists from the middle of summer into the fall. We found that four characteristics typical of a mountain meadow environment—low stream flow, open sky, cold groundwater discharge, and elevated organic carbon concentrations—are particularly conducive to pool stratification. Incoming shortwave radiation was the dominant energy input to heat pool water while nighttime emitted longwave radiation was the major cooling mechanism. Relatively cold groundwater discharge into the pool bottom increased density stratification within the pool. Elevated DOC concentrations increased the capacity of the pool to absorb photosynthetically active radiation and also promoted stratification. Stream velocities in the meadow were generally insufficient to meet threshold Richardson numbers and mix the pools during the daytime; smaller stream cross sectional areas would have potential for destabilizing pools in the daytime. We propose a conceptual model for describing polymictic stream pools and assessing the potential for polymictic pools to occur.

Raw project data is available by contacting ctemps@unr.edu

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Proof of concept: temperature-sensing waders for environmental sciences
Created: Dec. 29, 2017, 11:47 p.m.
Authors: Rolf Hut

ABSTRACT:

A prototype temperature-sensing pair of waders is introduced and tested. The water temperature at the streambed is interesting both for scientists studying the hyporheic zone and for, e.g., fishers spotting good fishing locations. A temperature sensor incorporated into waders worn by members of the public can give scientists an additional source of information on stream-water–groundwater interaction. A pair of waders was equipped with a thermistor and calibrated in the lab. Tests with both the waders and a reference thermometer in a deep polder ditch with a known localized groundwater contribution (i.e., boil) showed that the temperature-sensing waders are capable of identifying the boil location. However, the temperature-sensing waders showed a less pronounced response to changing water temperature compared to the reference thermometer, most likely due to the heat capacity of the person in the waders. This research showed that data from temperature-sensing waders worn by the public and shared with scientists can be used to decide where the most interesting places are to do more detailed and more expensive research.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

To better understand the groundwater resources of southern Nye County, Nevada, a multipart distributed thermal perturbation sensing (DTPS) test was performed on a complex of three wells. These wells penetrate an alluvial aquifer that drains the Nevada National Security Site, and characterizing the hydraulic properties and flow paths of the regional groundwater flow system has proven very difficult. The well complex comprised one pumping well and two observation wells, both located 18 m from the pumping well. Using fiber-optic cables and line heaters, DTPS tests were performed under both stressed and unstressed conditions. Each test injects heat into the water column over a period of one to two days, and observes the rising temperature during heat injection and falling temperatures after heating ceases. Aquifer thermal properties are inferred from temperature patterns in the cased section of the wells, and fluxes through the 30-m screened section are estimated based on a model that incorporates conductive and advective heat fluxes. Vertical variations in flux are examined on a scale of tens of cm. The actively flowing zones of the aquifer change between the stressed and unstressed test, and anisotropy in the aquifer permeability is apparent from the changing fluxes between tests. The fluxes inferred from the DTPS tests are compared to solute tracer tests previously performed on the same site. The DTPS-based fluxes are consistent with the fastest solute transport observed in the tracer test, but appear to overestimate the mean flux through the system.

Raw project data is available by contacting ctemps@unr.edu

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An Experimental Study of Transport in a Vineyard on a Hill - PTRAC 2014
Created: March 15, 2018, 10:50 p.m.
Authors: Drake, Steve · Miller, Nathan · Higgins, Chad

ABSTRACT:

The purpose of this project was to examine the transport of momentum, scalars, and heavy particles like fungal spores in a trellised agricultural canopy. To study these interactions, particle dispersion experiments were performed Sept 2-4, 2014 at Lone Star Vineyard (138 acres of wine grapes, 44 deg 4′ 8′′ N, 123 deg 5′ 48′′ W) near Amity, Oregon while high frequency wind and temperature data were collected.

Instruments:
-* Distributed Temperature Sensor fiber optic
- Sensornet Oryx: 1 m sampling resolution
- 900 micron AFL simplex fiber strung horizontally along _101 m_ vine at 6" vertical spacing at Tower 1
- 12 horizontal lengths looping through the baths (one cold, one ambient) at one end each time for the turn around
- DTS data starts at 11:28 on August 28th and ends at 12 on September 5, 2014. Up until 10:07 on September 1, only the first 898m of the fiber was captured, which corresponds to 7 lengths of fiber across the trellis. After 10:56, the DTS was reconfigured to write out data for the entire fiber length, corresponding to 12 fiber lengths.

- 3 Meteorological Towers
- 6 LEMS Towers
- Radiation Sensors (CNR1, LI200) at T1
- Soil sensors (HFP01, CS616, & TCAV) at T1
- 7 PAR sensors. 3 in canopy, 3 below at T1
- 18 Leaf surface temperature thermocouples

For more information on other aspects of the project:
Miller, N.E., Stoll, R., Mahaffee, W.F., Neill, T.M. and Pardyjak, E.R., 2015. An experimental study of momentum and heavy particle transport in a trellised agricultural canopy. Agricultural and forest meteorology, 211, 100-114. https://www.sciencedirect.com/science/article/pii/S0168192315001823
Miller, N.E., Stoll, R., Mahaffee, W.F. and Pardyjak, E.R., 2017. Mean and turbulent flow statistics in a trellised agricultural canopy. Boundary-Layer Meteorology, 165(1), pp.113-143. https://link.springer.com/article/10.1007/s10546-017-0265-y

Raw DTS project data is available by contacting ctemps@unr.edu

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Evaluation of Frost Protection at King Estate Vineyard using Distributed Temperature Sensing
Created: March 16, 2018, 3:44 p.m.
Authors: Predosa, Robert · Sayde, Chadi · Higgins, Chad

ABSTRACT:

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Aquatic habitats have a boundary layer near the air–water interface (AWI) that governs mass transport. Little is known about temperature profiles and boundary layers at the AWI. We used a high-resolution distributed temperature sensing (HR-DTS) system onboard an unmanned surface vehicle (USV) to resolve temperature profiles from about 1 m above and 1 m below the surface of the water. Our USV–HR-DTS system resolved a temperature differential of about 5.5 °C at the AWI, spanning a distance of approximately 13 cm. DTS profiles were similar for stationary holds and forward and reverse transects in the water. There was a significant change in temperature as a function of height, with an exponential decrease in temperature starting around 13 cm down to the AWI (P = 2 × 10−16). This is the first application of a HR-DTS onboard a USV to examine temperature profiles across the AWI. To our knowledge, these are the first high-resolution temperature profiles of the AWI captured from a mobile platform. Because our USV–HR-DTS system is mobile, it could be used to profile temperatures at the AWI at multiple locations in a large body of water. This technology could also find unique applications in the measurement of meteorological drivers of hazardous agent dispersal for source localization efforts.

Raw project data is available by contacting ctemps@unr.edu

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Measuring Tree Properties and Responses Using Low-Cost Accelerometers
Created: March 31, 2018, 7:44 p.m.
Authors: van Emmerik

ABSTRACT:

Trees play a crucial role in the water, carbon and nitrogen cycle on local, regional and global scales. Understanding the exchange of momentum, heat, water, and CO2 between trees and the atmosphere is important to assess the impact of drought, deforestation and climate change. Unfortunately, ground measurements of tree properties such as mass and canopy interception of precipitation are often expensive or difficult due to challenging environments. This paper aims to demonstrate the concept of using robust and affordable accelerometers to measure tree properties and responses. Tree sway is dependent on mass, canopy structure, drag coefficient, and wind forcing. By measuring tree acceleration, we can relate the tree motion to external forcing (e.g., wind, precipitation and related canopy interception) and tree physical properties (e.g., mass, elasticity). Using five months of acceleration data of 19 trees in the Brazilian Amazon, we show that the frequency spectrum of tree sway is related to mass, canopy interception of precipitation, and canopy–atmosphere turbulent exchange.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The Dead Sea is a hypersaline terminal lake, experiencing negative water balance, increasing salinity, and NaCl (halite) crystallization. We observed atypical evolution of the thermohaline stratification in comparison to most lakes due to the role of salt crystallization and diapycnal fluxes across lake layers. We characterized the dynamics of the thermohaline properties of the lake strata through high‐resolution continuous measurements of temperature profiles, novel water sampling methods, and observation of vertical profiles of salt crystallization. The diapycnal fluxes across the metalimnion were explained by Double Diffusion (DD) salt fingering driven by instability between warmer saltier water above cooler less salty water. The DD flux is associated with: (1) sharpening of the metalimnion from a 20 m wide transition in early summer, to staircase, ultimately merging to a single sharp sub‐meter step, (2) salinity decline from the epilimnion starting from mid‐summer synchronous with increasing salinity and temperature of the hypolimnion, and (3) active halite crystallization in the hypolimnion. We hypnotize that the salt fingering mechanism in saturated brines reveals a unique asymmetry; i.e., the descending cooling fingers become supersaturated and crystallize halite, whereas the ascending warming fingers becomes undersaturated. The DD flux in the Dead Sea is shown to be fundamental in the dynamics of stratification, providing a framework for general understanding DD flux in hypersaline environments. The finding that the epilimnion experiences seasonal halite undersaturation whereas the hypolimnion continuously precipitates salt by DD flux, has wide implications on the understanding of the dynamics of deposition of evaporitic rocks.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The heat pulse probe method can be implemented with actively heated fiber optics (AHFO) to obtain distributed measurements of soil water content (θ) by using reported soil thermal responses measured by Distributed Temperature Sensing (DTS) and with a soil‐specific calibration relationship. However, most reported applications have been calibrated to homogeneous soils in a laboratory, while inexpensive efficient in situ calibration procedures useful in heterogeneous soils are lacking. Here we employed the Hydrus 2‐D/3‐D code to define a soil‐specific calibration curve. We define a 2‐D geometry of the fiber optic cable and the surrounding soil media, and simulate heat pulses to capture the soil thermal response at different soil water contents. The model was validated in an irrigated field using DTS data from two locations along the FO deployment in which reference moisture sensors were installed. Results indicate that θ was measured with the model‐based calibration with accuracy better than 0.022 m3 m−3.

Raw project data is available by contacting ctemps@unr.edu

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Distributed Temperature Sensing as a downhole tool in hydrogeology
Created: March 31, 2018, 8:14 p.m.
Authors: Bense, V. F.

ABSTRACT:

Distributed Temperature Sensing (DTS) technology enables downhole temperature monitoring to study hydrogeological processes at unprecedentedly high frequency and spatial resolution. DTS has been widely applied in passive mode in site investigations of groundwater flow, in‐well flow, and subsurface thermal property estimation. However, recent years have seen the further development of the use of DTS in an active mode (A‐DTS) for which heat sources are deployed. A suite of recent studies using A‐DTS downhole in hydrogeological investigations illustrate the wide range of different approaches and creativity in designing methodologies. The purpose of this review is to outline and discuss the various applications and limitations of DTS in downhole investigations for hydrogeological conditions and aquifer geological properties. To this end, we first review examples where passive DTS has been used to study hydrogeology via downhole applications. Secondly, we discuss and categorize current A‐DTS borehole methods into three types. These are thermal advection tests, hybrid cable flow logging, and heat pulse tests. We explore the various options with regards to cable installation, heating approach, duration, and spatial extent in order to improve their applicability in a range of settings. These determine the extent to which each method is sensitive to thermal properties, vertical in‐well flow, or natural gradient flow. Our review confirms that the application of DTS has significant advantages over discrete point temperature measurements, particularly in deep wells, and highlights the potential for further method developments in conjunction with other emerging hydrogeophysical tools.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

We present one of the first studies of the use of distributed temperature sensing (DTS) along fibre-optic cables to purposely monitor spatial and temporal variations in ground surface temperature (GST) and soil temperature, and provide an estimate of the heat flux at the base of the canopy layer and in the soil. Our field site was at a groundwater-fed wet meadow in the Netherlands covered by a canopy layer (between 0 and 0.5 m thickness) consisting of grass and sedges. At this site, we ran a single cable across the surface in parallel 40 m sections spaced by 2 m, to create a 40 m × 40 m monitoring field for GST. We also buried a short length (≈10 m) of cable to depth of 0.1 ± 0.02 m to measure soil temperature. We monitored the temperature along the entire cable continuously over a two-day period and captured the diurnal course of GST, and how it was affected by rainfall and canopy structure. The diurnal GST range, as observed by the DTS system, varied between 20.94 and 35.08 °C; precipitation events acted to suppress the range of GST. The spatial distribution of GST correlated with canopy vegetation height during both day and night. Using estimates of thermal inertia, combined with a harmonic analysis of GST and soil temperature, substrate- and soil-heat fluxes were determined. Our observations demonstrate how the use of DTS shows great promise in better characterizing area-average substrate/soil heat flux, their spatiotemporal variability, and how this variability is affected by canopy structure. The DTS system is able to provide a much richer data set than could be obtained from point temperature sensors. Furthermore, substrate heat fluxes derived from GST measurements may be able to provide improved closure of the land surface energy balance in micrometeorological field studies. This will enhance our understanding of how hydrometeorological processes interact with near-surface heat fluxes.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

In situ soil moisture monitoring networks are critical to the development of soil moisture remote sensing missions as well as agricultural and environmental management, weather forecasting, and many other endeavors. These in situ networks utilize a variety of sensors and installation practices, which confounds the development of a unified reference database for satellite calibration and validation programs. As part of the Soil Moisture Active Passive Mission, the Marena, Oklahoma, In Situ Sensor Testbed (SMAP-MOISST) was initiated to perform inter-comparisons and study sensor limitations. Soil moisture sensors that are deployed in major monitoring networks were included in the study, along with new and emerging technologies, such as the Cosmic Ray Soil Moisture Observing System (COSMOS), passive/active distributed temperature sensing (DTS), and global positioning system reflectometers (GPSR). Four profile stations were installed in May of 2010, and soil moisture was monitored to a depth of 1 m on an hourly basis. The four stations were distributed within a circular domain of approximately 600 m diameter, adequate to encompass the sensing range of COSMOS. The sensors included in the base station configuration included the Stevens Water Hydra Probe, Campbell Scientific 616 and 229, Decagon EC-TM, Delta-T Theta Probe, Acclima, and Sentek EnviroSMART capacitance system. In addition, the Pico TRIME system and additional time-domain reflectometry (TDR) systems were deployed when available. It was necessary to apply site-specific calibration to most sensors to reach an RMSE below 0.04 m3 m−3. For most sensor types, a single near surface sensor could be scaled to represent the areal-average of a field domain by simple linear regression, resulting in RMSE values around 0.03 m3 m−3.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Fiber-optic distributed temperature sensing (DTS) makes it possible to observe temperatures on spatial scales as fine as centimeters and at frequencies up to 1 Hz. Over the past decade, fiber-optic DTS instruments have increasingly been employed to monitor environmental temperatures, from oceans to atmospheric monitoring. Because of the nature of environmental deployments, optical fibers deployed for research purposes often encounter step losses in the Raman spectra signal. Whether these phenomena occur due to cable damage or impingements, sharp bends in the deployed cable, or connections and splices, the step losses are usually not adequately addressed by the calibration routines provided by instrument manufacturers and can be overlooked in postprocessing calibration routines as well. Here we provide a method to identify and correct for the effects of step losses in raw Raman spectra data. The utility of the correction is demonstrated with case studies, including synthetic and laboratory data sets.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Aquatic ecosystems of North American deserts are frequently very restricted in area and tend to harbour very specialized species endemic to their restricted habitats. Small changes in environmental conditions of these specialized forms may jeopardize their persistence. A notable example of endemic and specialized species that may have been influenced by slight changes in its habitat is the Devils Hole pupfish (Cyprinodon diabolis), which occurs only in a small pool ecosystem in the Mojave Desert of the Southwestern United States. In this study, we use a computational fluid dynamic (CFD) model to examine the physical effects of climate change and local groundwater management on Devils Hole and combine those results with a conceptual ecological model to consider the impacts of those changes on annual recruitment of C. diabolis. The CFD model predicts water temperatures as a response to climate and water level, and the ecological model is used to determine the timing of tipping points that may encourage or suppress the annual recruitment of C. diabolis. The combination of interdisciplinary modelling approaches offers a method to quantify and compare the suitability of habitat under a range of management and climate scenarios. Our results show that the influence of water level on peak temperatures in Devils Hole (and on the ecosystem's suitability for C. diabolis) is an order of magnitude greater than the influence of climate change. Copyright © 2015 John Wiley & Sons, Ltd.

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Practical considerations for enhanced-resolution coil-wrapped distributed temperature sensing
Created: March 31, 2018, 8:47 p.m.
Authors: Hilgersom, K. P.

ABSTRACT:

Fibre optic distributed temperature sensing (DTS) is widely applied in Earth sciences. Many applications require a spatial resolution higher than that provided by the DTS instrument. Measurements at these higher resolutions can be achieved with a fibre optic cable helically wrapped on a cylinder. The effect of the probe construction, such as its material, shape, and diameter, on the performance has been poorly understood. In this article, we study data sets obtained from a laboratory experiment using different cable and construction diameters, and three field experiments using different construction characteristics. This study shows that the construction material, shape, diameter, and cable attachment method can have a significant influence on DTS temperature measurements. We present a qualitative and quantitative approximation of errors introduced through the choice of auxiliary construction, influence of solar radiation, coil diameter, and cable attachment method. Our results provide insight into factors that influence DTS measurements, and we present a number of solutions to minimize these errors. These practical considerations allow designers of future DTS measurement set-ups to improve their environmental temperature measurements.

Raw project data is available by contacting ctemps@unr.edu

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Meso-Scale Field Testing of Reactive Tracers in a Model Geothermal Reservoir
Created: March 31, 2018, 8:42 p.m.
Authors: Hawkins, A. J.

ABSTRACT:

Meso-scale field testing of thermally reactive tracers was conducted at the Altona field site in a well-characterized, single subhorizontal bedding plane fracture roughly 100 m2 in active area located 8 meters below ground surface. The spatial distribution of subsurface groundwater flow was previously characterized using ground penetrating radar (GPR) measurements. The reservoir rock, initially at 11.7 °C, was heated using 74 °C hot water injection in a two-spot pattern using an injection to production well separation of 14 m. During the heating process, a series of thermally degrading tracer experiments were used to characterize the progressive in situ heating of the fracture. In addition, a conservative, carbon-cored engineered nanoparticle tracer was used to measure the residence time distribution (RTD) of fluid flowing from injector to producer. Fiber Optic Distributed Temperature Sensing (FODTS) was used to continuously measure the spatial distribution of heat exchange at ten locations spread out between the injection and production well. The experiments revealed reduced recovery of the thermally degrading tracer as the reservoir was progressively heated indicating that the advancement of the thermal front was proportional to the mass fraction recovered of the thermally degrading tracer. Both GPR imaging and FODTS measurements reveal that flow was reduced to a narrow channel which directly connected the two flowing wells and led to early and rapid thermal breakthrough. Computational modeling of conservative/reactive tracer and heat transport in a two-dimensional discrete fracture demonstrate that subsurface characterization using conservative tracers alone could not uniquely characterize the Altona field site. The inclusion of the thermally reactive tracer, however, provided improved resolution of the spatial distribution of flow after 1 day of hot water injection.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Understanding the spatial and temporal characteristics of water flux into or out of shallow aquifers is imperative for water resources management and eco‐environmental conservation. In this study, the spatial variability in the vertical specific fluxes and hydraulic conductivities in a streambed were evaluated by integrating distributed temperature sensing (DTS) data and vertical hydraulic gradients into an ensemble Kalman filter (EnKF) and smoother (EnKS) and an empirical thermal‐mixing model. The formulation of the EnKF/EnKS assimilation scheme is based on a discretized 1D advection‐conduction equation of heat transfer in the streambed. We first systematically tested a synthetic case and performed quantitative and statistical analyses to evaluate the performance of the assimilation schemes. Then a real‐world case was evaluated to calculate assimilated specific flux. An initial estimate of the spatial distributions of the vertical hydraulic gradients was obtained from an empirical thermal‐mixing model under steady‐state conditions using a constant vertical hydraulic conductivity. Then, this initial estimate was updated by repeatedly dividing the assimilated specific flux by estimates of the vertical hydraulic gradients to obtain a refined spatial distribution of vertical hydraulic gradients and vertical hydraulic conductivities. Our results indicate that optimal parameters can be derived with fewer iterations but greater simulation effort using the EnKS compared with the EnKF. For the field application in a stream segment of the Heihe River Basin in northwest China, the average vertical hydraulic conductivities in the streambed varied over three orders of magnitude (5 × 10−1 to 5 × 102 m/d). The specific fluxes ranged from near zero (qz < ±0.05 m/d) to ±1.0 m/d, while the vertical hydraulic gradients were within the range of −0.2 to 0.15 m/m. The highest and most variable fluxes occurred adjacent to a debris‐dam and bridge pier. This phenomenon is very likely the result of heterogeneous streambed hydraulic characteristics in these areas. Our results have significant implications for hyporheic micro‐habitats, fish spawning and other wildlife incubation, regional flow and hyporheic solute transport models in the Heihe River Basin, as well as in other similar hydrologic settings.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

Soil temperature (Ts) exerts critical controls on hydrologic and biogeochemical processes, but the magnitude and nature of Ts variability in a landscape setting are rarely documented. Fiber-optic distributed temperature sensing (DTS) systems potentially measure Ts at high density across a large extent. A fiber-optic cable 771 m long was installed at a depth of 10 cm in contrasting landscape units (LUs) defined by vegetative cover at Upper Sheep Creek in the Reynolds Creek Experimental Watershed (RCEW) and Critical Zone Observatory in Idaho. The purpose was to evaluate the applicability of DTS in remote settings and to characterize Ts variability in complex terrain. Measurement accuracy was similar to other field instruments (±0.4°C), and Ts changes of approximately 0.05°C at a monitoring spatial scale of 1 m were resolved with occasional calibration and an ambient temperature range of 50°C. Differences in solar inputs among LUs were strongly modified by surface conditions. During spatially continuous snow cover, Ts was practically homogeneous across LUs. In the absence of snow cover, daily average Ts was highly variable among LUs due to variations in vegetative cover, with a standard deviation (SD) greater than 5°C, and relatively uniform (SD < 1.5°C) within LUs. Mean annual soil temperature differences among LUs of 5.2°C was greater than those of 4.4°C associated with a 910-m elevation difference within the RCEW. In this environment, effective Ts simulation requires representation of relatively small-scale (<20 m) LUs due to the deterministic spatial variability of Ts.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

The Salmon River is the second largest tributary of the Klamath River in northern California, USA. It is a region of steep mountains and diverse conifer forests. Historical land uses including logging, flow diversions, and hydraulic gold mining, have resulted in altered sediment transport regimes, diminished riparian cover and reduced large woody debris. These in turn have altered the thermal regime of the river. Summer stream temperatures commonly exceed salmonid (specifically Oncorhynchus spp.) temperature thresholds.

Study focus
Thermal dynamics of a one-kilometer reach of the Salmon River was quantified using distributed temperature sensing fiber-optics (DTS) and Heat Source modeling. Stream thermal responses to scenarios of air temperature increase and flow reduction were compared with riparian reforestation simulations to estimate benefits of reforestation.

New hydrological insights
Elevated air temperatures (2 °C, 4 °C, 6 °C) increased mean stream temperature by 0.23 °C/km, 0.45ºC/km and .68 °C/km respectively. Reforestation lowered temperatures 0.11–0.12 °C/km for partial and 0.26–0.27 °C/km for full reforestation. Reduced streamflow raised peak stream temperatures in all simulations. Warming could be mitigated by reforestation, however under severe flow reduction and warming (71.0 % reduction, 6 °C air temperature), only half of predicted warming would be reduced by the full reforestation scenario. Land managers should consider reforestation as a tool for mitigating both current and future warming conditions.

Raw project data is available by contacting ctemps@unr.edu

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ABSTRACT:

In recent years, wireline temperature profiling methods have evolved to offer new insight into fractured rock hydrogeology. Important advances in wireline temperature logging in boreholes make use of active line source heating alone and then in combination with temporary borehole sealing with flexible impervious fabric liners to eliminate the effects of borehole cross-connection and recreate natural flow conditions. Here, a characterization technique was developed based on combining fiber optic distributed temperature sensing (DTS) with active heating within boreholes sealed with flexible borehole liners. DTS systems provide a temperature profiling method that offers significantly enhanced temporal resolution when compared with conventional wireline trolling-based techniques that obtain a temperature–depth profile every few hours. The ability to rapidly and continuously collect temperature profiles can better our understanding of transient processes, allowing for improved identification of hydraulically active fractures and determination of relative rates of groundwater flow. The advantage of a sealed borehole environment for DTS-based investigations is demonstrated through a comparison of DTS data from open and lined conditions for the same borehole. Evidence for many depth-discrete active groundwater flow features under natural gradient conditions using active DTS heat pulse testing is presented along with high resolution geologic and geophysical logging and hydraulic datasets. Implications for field implementation are discussed.

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The MATERHORN: Unraveling the Intricacies of Mountain Weather
Created: March 31, 2018, 9:18 p.m.
Authors: Fernando, H. J. S.

ABSTRACT:

Emerging application areas such as air pollution in megacities, wind energy, urban security, and operation of unmanned aerial vehicles have intensified scientific and societal interest in mountain meteorology. To address scientific needs and help improve the prediction of mountain weather, the U.S. Department of Defense has funded a research effort—the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) Program—that draws the expertise of a multidisciplinary, multi-institutional, and multinational group of researchers. The program has four principal thrusts, encompassing modeling, experimental, technology, and parameterization components, directed at diagnosing model deficiencies and critical knowledge gaps, conducting experimental studies, and developing tools for model improvements. The access to the Granite Mountain Atmospheric Sciences Testbed of the U.S. Army Dugway Proving Ground, as well as to a suite of conventional and novel high-end airborne and surface measurement platforms, has provided an unprecedented opportunity to investigate phenomena of time scales from a few seconds to a few days, covering spatial extents of tens of kilometers down to millimeters. This article provides an overview of the MATERHORN and a glimpse at its initial findings. Orographic forcing creates a multitude of time-dependent submesoscale phenomena that contribute to the variability of mountain weather at mesoscale. The nexus of predictions by mesoscale model ensembles and observations are described, identifying opportunities for further improvements in mountain weather forecasting.

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High geothermal heat flux measured below the West Antarctic Ice Sheet
Created: March 31, 2018, 9:22 p.m.
Authors: Fisher, A. T.

ABSTRACT:

The geothermal heat flux is a critical thermal boundary condition that influences the melting, flow, and mass balance of ice sheets, but measurements of this parameter are difficult to make in ice-covered regions. We report the first direct measurement of geothermal heat flux into the base of the West Antarctic Ice Sheet (WAIS), below Subglacial Lake Whillans, determined from the thermal gradient and the thermal conductivity of sediment under the lake. The heat flux at this site is 285 ± 80 mW/m2, significantly higher than the continental and regional averages estimated for this site using regional geophysical and glaciological models. Independent temperature measurements in the ice indicate an upward heat flux through the WAIS of 105 ± 13 mW/m2. The difference between these heat flux values could contribute to basal melting and/or be advected from Subglacial Lake Whillans by flowing water. The high geothermal heat flux may help to explain why ice streams and subglacial lakes are so abundant and dynamic in this region.

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A field comparison of multiple techniques to quantify groundwater–surface-water interactions
Created: March 31, 2018, 9:25 p.m.
Authors: Gonzalez-Pinzon, R.

ABSTRACT:

AbstractGroundwater–surface-water (GW-SW) interactions in streams are difficult to quantify because of heterogeneity in hydraulic and reactive processes across a range of spatial and temporal scales. The challenge of quantifying these interactions has led to the development of several techniques, from centimeter-scale probes to whole-system tracers, including chemical, thermal, and electrical methods. We co-applied conservative and smart reactive solute-tracer tests, measurement of hydraulic heads, distributed temperature sensing, vertical profiles of solute tracer and temperature in the stream bed, and electrical resistivity imaging in a 450-m reach of a 3rd-order stream. GW-SW interactions were not spatially expansive, but were high in flux through a shallow hyporheic zone surrounding the reach. NaCl and resazurin tracers suggested different surface–subsurface exchange patterns in the upper ⅔ and lower ⅓ of the reach. Subsurface sampling of tracers and vertical thermal profiles quantified relatively high fluxes through a 10- to 20-cm deep hyporheic zone with chemical reactivity of the resazurin tracer indicated at 3-, 6-, and 9-cm sampling depths. Monitoring of hydraulic gradients along transects with MINIPOINT streambed samplers starting ∼40 m from the stream indicated that groundwater discharge prevented development of a larger hyporheic zone, which progressively decreased from the stream thalweg toward the banks. Distributed temperature sensing did not detect extensive inflow of ground water to the stream, and electrical resistivity imaging showed limited large-scale hyporheic exchange. We recommend choosing technique(s) based on: 1) clear definition of the questions to be addressed (physical, biological, or chemical processes), 2) explicit identification of the spatial and temporal scales to be covered and those required to provide an appropriate context for interpretation, and 3) maximizing generation of mechanistic understanding and reducing costs of implementing multiple techniques through collaborative research.

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ABSTRACT:

Technological advances in environmental sensing have increased our awareness of the complexity of spatial patterns and temporal dynamics of ecohydrological processes and their interactions. Improving the basis of knowledge of dynamically interacting processes is crucial for advancing our understanding of how ecosystems function under the influence of, and their resilience to, environmental change. Capturing the often fast changing and nonlinear behaviour of ecosystems represents a challenge for current observational networks, particularly when studying system interfaces and coupled ecological, hydrological, geomorphological and biogeochemical processes, demanding novel, adaptive approaches in real‐time monitoring and research. This paper discusses conceptual, technological and methodological challenges and resulting requirements for real‐time ecohydrological research by reviewing current approaches of capturing nonlinear behaviour with high‐frequency, high‐resolution monitoring and develops strategies for transforming ecohydrological research by including real‐time analysis of highly dynamic processes that are currently understudied. Examples of highly dynamic processes include rapid system changes, hot spots and hot moment behaviour.

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Groundwater–surface-water interactions: current research directions
Created: March 31, 2018, 9:33 p.m.
Authors: Larned, S. T.

ABSTRACT:

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Bed conduction impact on fiber optic distributed temperature sensing water temperature measurements
Created: March 31, 2018, 9:42 p.m.
Authors: O'Donnell Meininger, T.

ABSTRACT:

Error in distributed temperature sensing (DTS) water temperature measurements may be introduced by contact of the fiber optic cable sensor with bed materials (e.g., seafloor, lakebed, streambed). Heat conduction from the bed materials can affect cable temperature and the resulting DTS measurements. In the Middle Fork John Day River, apparent water temperature measurements were influenced by cable sensor contact with aquatic vegetation and fine sediment bed materials. Affected cable segments measured a diurnal temperature range reduced by 10% and lagged by 20–40 min relative to that of ambient stream temperature. The diurnal temperature range deeper within the vegetation–sediment bed material was reduced 70% and lagged 240 min relative to ambient stream temperature. These site-specific results illustrate the potential magnitude of bed-conduction impacts with buried DTS measurements. Researchers who deploy DTS for water temperature monitoring should understand the importance of the environment into which the cable is placed on the range and phase of temperature measurements.

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ABSTRACT:

We develop an approach for measuring in-well fluid velocities using point electrical heating combined with spatially and temporally continuous temperature monitoring using Distributed Temperature Sensing (DTS). The method uses a point heater to warm a discrete volume of water. The rate of advection of this plume, once the heating is stopped, equates to the average flow velocity in the well. We conducted Thermal-Plume fibre Optic Tracking (T-POT) tests in a borehole in a fractured rock aquifer with the heater at the same depth and multiple pumping rates. Tracking of the thermal plume peak allowed the spatially varying velocity to be estimated up to 50 m downstream from the heating point, depending on the pumping rate. The T-POT technique can be used to estimate the velocity throughout long intervals provided that thermal dilution due to inflows, dispersion, or cooling by conduction do not render the thermal pulse unresolvable with DTS. A complete flow log may be obtained by deploying the heater at multiple depths, or with multiple point heaters.

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High‐resolution wind speed measurements using actively heated fiber optics
Created: March 31, 2018, 9:49 p.m.
Authors: Sayde, C.

ABSTRACT:

We present a novel technique to simultaneously measure wind speed (U) at thousands of locations continuously in time based on measurement of velocity‐dependent heat transfer from a heated surface. Measuring temperature differences between paired passive and actively heated fiber‐optic (AHFO) cables with a distributed temperature sensing system allowed estimation of U at over 2000 sections along the 230 m transect (resolution of 0.375 m and 5.5 s). The underlying concept is similar to that of a hot wire anemometer extended in space. The correlation coefficient between U measured by two colocated sonic anemometers and the AHFO were 0.91 during the day and 0.87 at night. The combination of classical passive and novel AHFO provides unprecedented dynamic observations of both air temperature and wind speed spanning 4 orders of magnitude in spatial scale (0.1–1000 m) while resolving individual turbulent motions, opening new opportunities for testing basic theories for near‐surface geophysical flows.

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ABSTRACT:

The delineation of groundwater discharge areas based on Distributed Temperature Sensing (DTS) data of the streambed can be difficult in soft‐bedded streams where sedimentation and scouring processes constantly change the position of the fibre optic cable relative to the streambed. Deposition‐induced temperature anomalies resemble the signal of groundwater discharge while scouring will cause the cable to float in the water column and measure stream water temperatures. DTS applied in a looped layout with nine fibre optic cable rows in a 70 × 5 m section of a soft‐bedded stream made it possible to detect variability in streambed temperatures between October 2011 and January 2012. Detailed monthly streambed elevation surveys were carried out to monitor the position of the fibre optic cable relative to the streambed and to quantify the effect of sedimentation processes on streambed temperatures. Based on the simultaneous interpretation of streambed temperature and elevation data, a method is proposed to delineate potential high‐groundwater discharge areas and identify deposition‐induced temperature anomalies in soft‐bedded streams. Potential high‐discharge sites were detected using as metrics the daily minimum, maximum and mean streambed temperatures as well as the daily amplitude and standard deviation of temperatures. The identified potential high‐discharge areas were mostly located near the channel banks, also showing temporal variability because of the scouring and redistribution of streambed sediments, leading to the relocation of pool‐riffle sequences. This study also shows that sediment deposits of 0.1 m thickness already resulted in an increase in daily minimum streambed temperatures and decrease in daily amplitude and standard deviation. Scouring sites showed lower daily minimum streambed temperatures and higher daily amplitude and standard deviation compared with areas without sedimentation and scouring. As a limitation of the approach, groundwater discharge occurring at depositional and scouring areas cannot be identified by the metrics applied.

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Evaluating the Use of In‐Well Heat Tracer Tests to Measure Borehole Flow Rates
Created: March 31, 2018, 9:56 p.m.
Authors: Sellwood, S. M.

ABSTRACT:

Recent research has demonstrated the use of in‐well heat tracer tests monitored by a fiber optic distributed temperature sensing (DTS) system to characterize borehole flow conditions in open bedrock boreholes. However, the accuracy of borehole flow rates determined from in‐well heat tracer tests has not been evaluated. The purpose of the research presented here is to determine whether borehole flow rates obtained using DTS‐monitored in‐well heat tracer tests are reasonable, and to evaluate the range of flow rates measureable with this method. To accomplish this, borehole flow rates measured using in‐well heat tracer tests are compared to borehole flow rates measured in the same boreholes using an impeller or heat pulse flowmeter. A comparison of flow rates measured using in‐well heat tracer tests to flow rates measured with an impeller flowmeter under the same conditions showed good agreement. A comparison of in‐well heat tracer test flow rate measurements to previously‐collected heat pulse flowmeter measurements indicates that the heat tracer test results produced borehole flow rates and flow profiles similar to those measured with the heat pulse flowmeter. The results of this study indicate that borehole flow rates determined from DTS‐monitored in‐well heat tracer tests are reasonable estimates of actual borehole flow rates. In addition, the range of borehole flow rates measurable by in‐well heat tracer tests spans from less than 10−1 m/min to approximately 101 m/min, overlapping the ranges typically measurable with an impeller flowmeter or a heat pulse flowmeter, making in‐well heat tracer testing a versatile borehole flow logging tool.

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Renewable water: Direct contact membrane distillation coupled with solar ponds
Created: March 31, 2018, 10:49 p.m.
Authors: Suarez, F.

ABSTRACT:

Desalination powered by renewable energy sources is an attractive solution to address the worldwide water-shortage problem without contributing significant to greenhouse gas emissions. A promising system for renewable energy desalination is the utilization of low-temperature direct contact membrane distillation (DCMD) driven by a thermal solar energy system, such as a salt-gradient solar pond (SGSP). This investigation presents the first experimental study of fresh water production in a coupled DCMD/SGSP system. The objectives of this work are to determine the experimental fresh water production rates and the energetic requirements of the different components of the system. From the laboratory results, it was found that the coupled DCMD/SGSP system treats approximately six times the water flow treated by a similar system that consisted of an air–gap membrane distillation unit driven by an SGSP. In terms of the energetic requirements, approximately 70% of the heat extracted from the SGSP was utilized to drive thermal desalination and the rest was lost in different locations of the system. In the membrane module, only half of the useful heat was actually used to transport water across the membrane and the remainder was lost by conduction in the membrane. It was also found that by reducing heat losses throughout the system would yield higher water fluxes, pointing out the need to improve the efficiency throughout the DCMD/SGSP coupled system. Therefore, further investigation of membrane properties, insulation of the system, or optimal design of the solar pond must be addressed in the future.

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ABSTRACT:

AbstractThe effect of proglacial groundwater systems on surface hydrology and ecology in cold regions often is neglected when assessing the ecohydrological implications of climate change. We present a novel approach in which we combined 2 temperature-tracing techniques to assess the spatial patterns and short-term temporal dynamics of groundwater–surface-water exchange in the proglacial zone of Skaftafellsjökull, a retreating glacier in southeastern Iceland. Our study focuses on localized groundwater discharge to a surface-water environment, where high temporal- and spatial-resolution mapping of sediment surface and subsurface temperatures (10–15 cm depth) were obtained by Fiber-Optic Distributed Temperature Sensing (FO-DTS). The FO-DTS survey identified temporally consistent locations of temperature anomalies at the sediment–water interface, indicating distinct zones of cooler groundwater upwelling. The high-resolution FO-DTS surveys were combined with calculations of 1-dimensional groundwater seepage fluxes based on 3 vertical sediment temperature profiles, covering depths of 10, 25, and 40 cm below the lake bed. The calculated groundwater seepage rates ranged between 1.02 to 6.10 m/d. We used the combined techniques successfully to identify substantial temporal and spatial heterogeneities in groundwater–surface exchange fluxes that have relevance for the ecohydrological functioning of the investigated system and its potential resilience to environmental change.

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ABSTRACT:

The evolution of cold air layers near the surface was investigated for a night with stable conditions near the surface. Spatial air temperature observations at 276 co-located vertical profiles were made using high-resolution fibre-optic based distributed temperature sensing (DTS) in a quasi three-dimensional geometry oriented along a shallow depression in the landscape and analysed for patterns in near-surface flow. Temperature stratification was observed to be interrupted by transient temperature structures on the scale of metres for which the flow direction and velocity could be quantified. The high spatial resolution and large spatial domain of the DTS revealed temperature structures in a level of detail that exceeded the capability of traditional point observations of air temperature at low wind speeds. Further, composition techniques were applied to describe wave-like motions in the opposite direction of the mean flow, at intervals of approximately 200 s (5 mHz). The DTS technique delivered tomography on a scale of tens of metres. The spatial observations at high spatial (fractions of a metre) and temporal (sec) resolution provided new opportunities for detection and quantification of surface-flow features and description of complicated scale interactions. High-resolution DTS is therefore a valuable addition to experimental research on stable and weak-wind boundary layers near the surface.

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Quantity and quality of groundwater discharge in a hypersaline lake environment
Created: March 31, 2018, 10:59 p.m.
Authors: Anderson, R. B.

ABSTRACT:

Geophysical and geochemical surveys were conducted to understand groundwater discharge to Great Salt Lake (GSL) and assess the potential significance of groundwater discharge as a source of selenium (Se). Continuous resistivity profiling (CRP) focusing below the sediment/water interface and fiber-optic distributed temperature sensing (FO-DTS) surveys were conducted along the south shore of GSL. FO-DTS surveys identified persistent cold-water temperature anomalies at 10 separate locations. Seepage measurements were conducted at 17 sites (mean seepage rate = 0.8 cm/day). High resistivity anomalies identified by the CRP survey were likely a mirabilite (Na2SO4·10H2O) salt layer acting as a semi-confining layer for the shallow groundwater below the south shore of the lake. Positive seepage rates measured along the near-shore areas of GSL indicate that a ∼1-m thick oolitic sand overlying the mirabilite layer is likely acting as a shallow, unconfined aquifer. Using the average seepage rate of 0.8 cm/day over an area of 1.6 km2, an annual Se mass loading to GSL of 23.5 kg was estimated. Determination of R/Ra values (calculated 3He/4He ratio over the present-day atmospheric 3He/4He ratio) <1 and tritium activities of 1.2–2.0 tritium units in groundwater within and below the mirabilite layer indicates a convergence of regional and local groundwater flow paths discharging into GSL. Groundwater within and below the mirabilite layer obtains its high sulfate salinity from the dissolution of mirabilite. The δ34S and δ18O isotopic values in samples of dissolved sulfate from the shallow groundwater below the mirabilite are almost identical to the isotopic signature of the mirabilite core material. The saturation index calculated for groundwater samples using PHREEQC indicates the water is at equilibrium with mirabilite. Water samples collected from GSL immediately off shore contained Se concentrations that were 3–4 times higher than other sampling sites >25 km offshore from the study site and may be originating from less saline groundwater seeps mixing with the more saline water from GSL. Additional evidence for mixing with near shore seeps is found in the δD and δ18O isotopic values and Br:Cl ratios. Geochemical modeling for a water sample collected in the vicinity of the study area indicates that under chemically reducing conditions, arsenic- (As) bearing minerals could dissolve while Se-bearing minerals will likely precipitate out of solution, possibly explaining why the shallow groundwater below and within the mirabilite salt layer contains low concentrations of Se (0.9–2.3 μg/L).

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High‐resolution temperature sensing in the Dead Sea using fiber optics
Created: March 31, 2018, 11:04 p.m.
Authors: Arnon, A.

ABSTRACT:

The thermal stratification of the Dead Sea was observed in high spatial and temporal resolutionby means of fiber-optics temperature sensing. The aim of the research was to employ the novel high-resolution profiler in studying the dynamics of the thermal structure of the Dead Sea and the related proc-esses including the investigation of the metalimnion fluctuations. The 18 cm resolution profiling systemwas placed vertically through the water column supported by a buoy 450 m from shore, from 2 m above to53 m below the water surface (just above the local seafloor), covering the entire seasonal upper layer (themetalimnion had an average depth of 20 m). Temperature profiles were recorded every 5 min. The May toJuly 2012 data set allowed quantitative investigation of the thermal morphology dynamics, including objec-tive definitions of key locations within the metalimnion based on the temperature depth profile and its firstand second depth derivatives. Analysis of the fluctuation of the defined metalimnion locations showed strong anticorrelation to measured sea level fluctuations. The slope of the sea level versus metalimniondepth was found to be related to the density ratio of the upper layer and the underlying main water body,according to the prediction of a two-layer model. The heat content of the entire water column was calcu-lated by integrating the temperature profiles. The vertically integrated apparent heat content was seen tovary by 50% in a few hours. These fluctuations were not correlated to the atmospheric heat fluxes, nor tothe momentum transfer, but were highly correlated to the metalimnion and the sea level fluctuations(r 5 0.84). The instantaneous apparent heat flux was 3 orders of magnitude larger than that delivered byradiation, with no direct correlation to the frequency of radiation and wind in the lake. This suggests thatthe source of the momentary heat flux is lateral advection due to internal waves (with no direct relation tothe diurnal cycle). In practice, it is shown that snap-shot profiles of the Dead Sea as obtained with standardthermal profilers will not represent the seasonal typical status in terms of heat content of the upper layer.

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ABSTRACT:

Spatial resolution fiber‐optic cables allow for detailed observation of thermally complex heterogeneous hydrologic systems. A commercially produced high spatial resolution helically wound optic fiber sensing cable is employed in the Dead Sea, in order to study the dynamics of thermal stratification of the hypersaline lake. Structured spatial artifacts were found in the data from the first 10 m of cable (110 m of fiber length) following the transition from straight fiber optic. The Stokes and Anti‐Stokes signals indicate that this is the result of differential attenuation, thought to be due to cladding losses. Though the overall spatial form of the loss was consistent, the fine structure of the loss changed significantly in time, and was strongly asymmetrical, and thus was not amenable to standard calibration methods. Employing the fact that the cable was built with a duplex construction, and using high‐precision sensors mounted along the cable, it was possible to correct the artifact in space and time, while retaining the high‐quality of data obtained in the early part of the cable (prior to significant optical attenuation). The defect could easily be overlooked; however, reanalyzing earlier experiments, we have observed the same issue with installations employing similar cables in Oregon and France, so with this note we both alert the community to this persistent concern and provide an approach to correct the data in case of similar problems.

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Induced Temperature Gradients to Examine Groundwater Flowpaths in Open Boreholes
Created: March 31, 2018, 11:12 p.m.
Authors: Arnon, A.

ABSTRACT:

Techniques for characterizing the hydraulic properties and groundwater flow processes of aquifers are essential to design hydrogeologic conceptual models. In this study, rapid time series temperature profiles within open‐groundwater wells in fractured rock were measured using fiber optic distributed temperature sensing (FO‐DTS). To identify zones of active groundwater flow, two continuous electrical heating cables were installed alongside a FO‐DTS cable to heat the column of water within the well and to create a temperature difference between the ambient temperature of the groundwater in the aquifer and that within the well. Additional tests were performed to examine the effects of pumping on hydraulic fracture interconnectivity around the well and to identify zones of increased groundwater flow. High‐ and low‐resolution FO‐DTS cable configurations were examined to test the sensitivities of the technique and compared with downhole video footage and geophysical logging to confirm the zones of active groundwater flow. Two examples are presented to demonstrate the usefulness of this new technique for rapid characterization of fracture zones in open boreholes. The combination of the FO‐DTS and heating cable has excellent scope as a rapid appraisal tool for borehole construction design and improving hydrogeologic conceptual models.

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Induced Temperature Gradients to Examine Groundwater Flowpaths in Open Boreholes
Created: March 31, 2018, 11:16 p.m.
Authors: Banks, E. W.

ABSTRACT:

Techniques for characterizing the hydraulic properties and groundwater flow processes of aquifers are essential to design hydrogeologic conceptual models. In this study, rapid time series temperature profiles within open‐groundwater wells in fractured rock were measured using fiber optic distributed temperature sensing (FO‐DTS). To identify zones of active groundwater flow, two continuous electrical heating cables were installed alongside a FO‐DTS cable to heat the column of water within the well and to create a temperature difference between the ambient temperature of the groundwater in the aquifer and that within the well. Additional tests were performed to examine the effects of pumping on hydraulic fracture interconnectivity around the well and to identify zones of increased groundwater flow. High‐ and low‐resolution FO‐DTS cable configurations were examined to test the sensitivities of the technique and compared with downhole video footage and geophysical logging to confirm the zones of active groundwater flow. Two examples are presented to demonstrate the usefulness of this new technique for rapid characterization of fracture zones in open boreholes. The combination of the FO‐DTS and heating cable has excellent scope as a rapid appraisal tool for borehole construction design and improving hydrogeologic conceptual models.

Raw project data is available by contacting ctemps@unr.edu

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Heated Fiber Optic Distributed Temperature Sensing: A Dual-Probe Heat-Pulse Approach
Created: March 31, 2018, 11:19 p.m.
Authors: Benitez-Buelga, J. B.

ABSTRACT:

Implementation of the dual-probe heat-pulse (DPHP) approach for measurement of volumetric heat capacity (C) and water content (θ) with distributed temperature sensing heated fiber optic (FO) systems presents an unprecedented opportunity for environmental monitoring (e.g., simultaneous measurement at thousands of points). We applied uniform heat pulses along a FO cable and monitored the thermal response at adjacent cables. We tested the DPHP method in the laboratory using multiple FO cables at a range of spacings. The amplitude and phase shift in the heat signal with distance was found to be a function of the soil volumetric heat capacity. Estimations of C at a range of moisture contents (θ = 0.09– 0.34 m3 m−3) suggest the feasibility of measurement via responsiveness to the changes in θ, although we observed error with decreasing soil water contents (up to 26% at θ = 0.09 m3 m−3). Optimization will require further models to account for the finite radius and thermal influence of the FO cables. Although the results indicate that the method shows great promise, further study is needed to quantify the effects of soil type, cable spacing, and jacket configurations on accuracy.

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ABSTRACT:

The Devils Hole pupfish (Cyprinodon diabolis) is a federally listed endangered species living solely within the confines of Devils Hole, a geothermal pool ecosystem in the Mojave Desert of the American Southwest. This unique species has suffered a significant, yet unexplained, population decline in the past two decades, with a record low survey of 35 individuals in early 2013. The species survives on a highly variable seasonal input of nutrients and has evolved in a thermal regime lethal to other pupfish species. The short lifespan of the species (approximately 1 year) makes annual recruitment in Devils Hole critical to the persistence of the species, and elevated temperatures on the shallow shelf that comprises the optimal spawning habitat in the ecosystem can significantly reduce egg viability and increase larval mortality. Here we combine computational fluid dynamic modeling and ecological analysis to investigate the timing of thresholds in the seasonal cycles of food supply and temperature. Numerical results indicate a warming climate most impacts the heat loss from the water column, resulting in warming temperatures and reduced buoyancy‐driven circulation. Observed climate change is shown to have already warmed the shallow shelf, and climate change by 2050 is shown to shorten the window of optimum conditions for recruitment by as much as 2 weeks. While there are many possible reasons for the precipitous decline of this species, the changing climate of the Mojave region is shown to produce thermal and nutrient conditions likely to reduce the success of annual recruitment of young C. diabolis in the future, leading to continued threats to the survival of this unique and enigmatic species.

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ABSTRACT:

Supraglacial channel networks link time varying melt production and meltwater routing on temperate glaciers. Such channel networks often include components of both surface transport in streams and subsurface porous flow through near-surface ice, firn or snowpack. Although subsurface transport if present will likely control network transport efficacy, it is the most poorly characterized component of the system. We present measurements of supraglacial channel spacing and network properties on the Juneau Icefield, subsurface water table height, and time variation of hydraulic characteristics including diurnal variability in water temperature. We combine these data with modeling of porous flow in weathered ice to infer near-surface permeability. Estimates are based on an observed phase lag between diurnal water temperature variations and discharge, and independently on measurement of water table surface elevation away from a stream. Both methods predict ice permeability on a 1–10 m scale in the range of 10−10–10−11 m2. These estimates are considerably smaller than common parameterizations of surface water flow on bare ice in the literature, as well as smaller than most estimates of snowpack permeability. For supraglacial environments in which porosity/permeability creation in the subsurface is balanced by porous flow of meltwater, our methods provide an estimate of microscale hydraulic properties from observations of supraglacial channel spacing.

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ABSTRACT:

Measuring basal melting of ice shelves is challenging and represents a critical component toward understanding ocean‐ice interactions and climate change. In November 2011, moorings containing fiber‐optic cables for distributed temperature sensing (DTS) were installed through the McMurdo Ice Shelf, Antarctica, (~200 m) and extending ~600 m into the ice shelf cavity. The high spatial resolution of DTS allows for transient monitoring of the thermal gradient within the ice shelf. The gradient near the ice‐ocean interface is extrapolated to the in situ freezing temperature in order to continuously track the ice‐ocean interface. Seasonal melt rates are calculated to be ~1.0 mm d−1 and 8.6 mm d−1, and maximum melting corresponds to the arrival of seasonal warm surface water in the ice shelf cavity between January and April. The development of continuous, surface‐based techniques for measuring basal melting represents a significant advance in monitoring ice shelf stability and ice‐ocean interactions.

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ABSTRACT:

This paper introduces the special section on “new modeling approaches and novel experimental technologies for improved understanding of process dynamics at aquifer‐surface water interfaces.” It is contextualizing the framework for the 27 research papers of the special section by firth identifying research gaps and imminent challenges for ecohydrological research at aquifer‐surface water interfaces and then discussing the specific paper contributions on (i) new developments in temperature/heat tracing at GW‐SW interfaces, (ii) new methods to capture the temporal and spatial variability of groundwater—surface water exchange, (iii) new approaches in modeling aquifer‐river exchange flow, and (iv) new concepts and advanced theory of groundwater—surface water exchange.

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ABSTRACT:

We thank J. S. Selker et al. (Comment on “Capabilities and limitations of tracing spatial temperature 1 patterns by fiber‐optic distributed temperature sensing” by Liliana Rose et al., hereinafter cited as “Selker et al. [2014]”) for their insightful comment on the Rose et al. [2013] technical note, which provides a helpful perspective on some instrumental performance aspects of Fiber‐optic Distributed Sensing (FO‐DTS).

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ABSTRACT:

The distribution of groundwater inflows in a stream reach plays a major role in controlling the stream temperature, a vital component shaping the riverine ecosystem. In this study, the Distributed Temperature Sensing (DTS) system was installed in a small Danish lowland stream, Elverdamsåen, to assess the seasonal dynamics of groundwater inflow zones using high spatial (1 m) and temporal (3 minutes) resolution of water temperature measurements. Four simple criteria consisting of 30 min average temperature at 16:00, mean and standard deviation of diurnal temperatures, and the day–night temperature difference were applied to three DTS datasets representing stream temperature responses to the variable meteorological and hydrological conditions prevailing in summer, winter and spring. The standard deviation criterion was useful to identify groundwater discharge zones in summer and spring conditions, while the mean temperature criterion was better for the winter conditions. In total, 20 interactions were identified from the DTS datasets representing summer, 16 in winter and 19 in spring, albeit with only two interactions contributing in all three seasons. Higher baseflow to streamflow ratio, antecedent precipitation and presence of fractured clayey till in the stream reach were deemed as the vital factors causing apparent seasonal variation in the locations of upwelling zones, prompting use of DTS not only in preconceived scenarios of large diurnal temperature change but rather a long‐term deployment covering variable meteorological and hydrological scenarios.

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Advancing Groundwater Technology on the Prairie
Created: March 31, 2018, 11:46 p.m.
Authors: Miller, G. D.

ABSTRACT:

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ABSTRACT:

We show how a distributed borehole flowmeter can be created from armored Fiber Optic cables with the Active‐Distributed Temperature Sensing (A‐DTS) method. The principle is that in a flowing fluid, the difference in temperature between a heated and unheated cable is a function of the fluid velocity. We outline the physical basis of the methodology and report on the deployment of a prototype A‐DTS flowmeter in a fractured rock aquifer. With this design, an increase in flow velocity from 0.01 to 0.3 m s−1 elicited a 2.5°C cooling effect. It is envisaged that with further development this method will have applications where point measurements of borehole vertical flow do not fully capture combined spatiotemporal dynamics.

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ABSTRACT:

Studies of surface water–groundwater interactions using fiber optic distributed temperature sensing (FO-DTS) has increased in recent years. However, only a few studies to date have explored the limitations of FO-DTS in detecting groundwater discharge to 5 streams. A FO_DTS system was therefore tested in a flume under controlled laboratory conditions for its ability to accurately measure the discharge of hot or cold groundwater into a simulated surface water flow. In the experiment the surface water (SW) and groundwater (GW) velocities, expressed as ratios (vgw/vsw), were varied from 0.21 % to 61.7 %; temperature difference between SW-GW were varied from 2 to 10 ◦C; the 10 direction of temperature gradient were varied with both cold and-hot water injection; and two different bed materials were used to investigate their effects on FO_DTS’s detection limit of groundwater discharge. The ability of the FO_DTS system to detect the discharge of groundwater of a different temperature in the laboratory environment was found to be mainly dependent upon the surface and groundwater flow velocities and 15 their temperature difference. A correlation was proposed to estimate the groundwater discharge from temperature. The correlation is valid when the ratio of the apparent temperature response to the source temperature difference is above 0.02

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Evaporation suppression and solar energy collection in a salt-gradient solar pond
Created: March 31, 2018, 11:59 p.m.
Authors: Ruskowitz, J. A.

ABSTRACT:

Evaporation represents a significant challenge to the successful operation of solar ponds. In this work, the suppression of evaporative losses from a salt-gradient solar pond was investigated in the laboratory. Two floating element designs (floating discs and floating hemispheres) and a continuous cover were tested; all three covers/elements were non-opaque, which is unique from previous studies of evaporation suppression in ponds or pools where increasing temperature and heat content are not desired. It was found that floating discs were the most effective element; full (88%) coverage of the solar pond with the floating discs decreases the evaporation rate from 4.8 to 2.5 mm/day (47% decrease), increases the highest achieved temperature from 34 °C to 43 °C (26% increase), and increases heat content from 179 to 220 MJ (22% increase). As a result of reduced evaporative losses at the surface, the amount of heat lost to the atmosphere is also reduced, which results in lower conductive losses from the NCZ and the LCZ and hence, increased temperatures in the NCZ and LCZ. The magnitude of evaporation reduction observed in this work is important as it may enable solar pond operation in locations with limited water supply for replenishment. The increase in heat content allows more heat to be withdrawn from the pond for use in external applications, which significantly improves the thermal efficiencies of solar ponds.

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ABSTRACT:

Solar ponds are low-cost, large-scale solar collectors with integrated storage that can be used as an energy source in many thermal systems. Experimental solar pond investigations at smaller scales have proven to be useful when trying to understand how different factors affect the pond’s efficiency, but they do not necessarily represent the expected performance of large-scale solar ponds. Consequently, it is important to investigate how the results of small-scale solar pond experiments can be scaled up. In this work, we show how models based on laboratory-scale observations can be utilized to understand the expected performance of large-scale solar ponds. This paper presents an approach that combines high-resolution thermal observations with computational fluid dynamics to investigate how different physical processes affect solar pond performance at different scales. The main factors that result in differences between small- and large-scale solar pond performances are boundary effects, light radiation spectrum and intensity, and turbidity. Boundary effects (e.g., pond geometry, thermal insulation) reduce the energy that reaches the storage zone of small-scale solar ponds. Different types of lights result in different radiation spectrum and intensity, which affects the energy reaching the storage zone. Turbidity is typically not important in small-scale solar ponds subject to controlled environmental conditions. However, it is an important factor in outdoor solar ponds in which the pond is prone to particles that can deposit onto the water surface or become suspended in the gradient zone. In general, the combination of these factors results in less energy collected in small-scale solar ponds than in large-scale solar ponds, even though large-scale solar ponds are typically subject to more extreme environmental conditions. High-resolution thermal observations combined with numerical simulations to understand the expected performance of large-scale solar ponds seems to be a promising tool for improving both efficiency and operation of these solar energy systems.

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Characterizing preferential groundwater discharge through boils using temperature
Created: April 1, 2018, 4:35 p.m.
Authors: Vandenbohede, A.

ABSTRACT:

In The Netherlands, preferential groundwater discharge trough boils is a key process in the salinization of deep polders. Previous work showed that boils also influence the temperature in the subsurface and of surface water. This paper elaborates on this process combining field observations with numerical modeling. As is the case for salinity, a distinct anomaly in the subsurface and surface water temperature can be attributed to boils. Lines of equal temperature are distorted towards the boil, which can be considered as an upconing of the temperature profile by analogy of the upconing of a fresh–saltwater interface. The zone of this distortion is limited to the immediate vicinity of the boil, being about 5 m in the aquitard which holds the boil’s conduit, or maximum a few dozens of meters in the underlying aquifer. In the aquitard, heat transport is conduction dominated whereas this is convection dominated in the aquifer. The temperature anomaly differs from the salinity anomaly by the smaller radius of influence and faster time to reach a new steady-state of the former. Boils discharge water with a temperature equal to the mean groundwater temperature. This influences the yearly and diurnal variation of ditch water temperature in the immediate vicinity of the boil importantly but also the temperature in the downstream direction. Temporary nature of the boil (e.g. stability of the conduit, discharge rate), uncertainty on the 3D construction of the conduit and heterogeneity of the subsoil make it unlikely that temperature measurements can be interpreted further than a qualitative level.

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New technique for access-borehole drilling in shelf glaciers using lightweight drills
Created: April 1, 2018, 4:46 p.m.
Authors: Zagorodnov, V.

ABSTRACT:

This paper describes a new, environmentally friendly drilling technique for making short-and long-term access boreholes in shelf glaciers using lightweight drills. The new drilling technique was successfully developed for installation of small-diameter sensors under the Ross Ice Shelf through ~ 193 m thick ice at Windless Bight, McMurdo Ice Shelf, Antarctica. The two access boreholes were drilled and sensors installed in 110 working hours. The total weight of the drilling equipment including the power system and fuel is <400 kg. Installation of small-diameter sensors was possible for 1.8– 6 hours after penetration through the glacier into the sea water beneath. The new drilling technique does not require drilling fluid and therefore has minimal environmental impact. It should permit access through ice-shelf ice up to 350 m thick, or glaciers on grounded ice or subglacial lakes if there is no water-permeable interface at the base. Modifications, presented in this work, of the drilling equipment and protocol will allow for (1) ~ 21 working hours for penetration through 200 m of ice, (2) installation of sensors up to 120 mm in diameter and (3) drilling long-term open boreholes through 400 m thick ice in 100 working hours.

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ABSTRACT:

This study employed Distributed Temperature Sensing (DTS) and Heat Source modeling to quantify the thermal regime of a one-kilometer section of the North Fork of the Salmon River, a tributary of the Klamath River, northern California, USA. The study collected eight days of temperature data using DTS at one-meter, 15-minute intervals during July 2012. The research aimed to: 1) investigate the geomorphic and thermal conditions of the study reach and their impact on native Salmonids. 2) identify and quantify groundwater seeps; and 3) employ and calibrate Heat Source to predict effects of riparian management, channel geometry, and climate change on stream temperature over the study reach. DTS observations revealed nearly uniform warming over the study reach, a diel heating cycle of 5 °C, a small groundwater spring (7 % of mainstem flow), and a Maximum Weekly Maximum Temperature (MWMT) of 23.00 °C. Statistical modeling of salmonid distribution field observations with AICc found that depth was the most explanatory parameter. Habitat inventory of the study reach indicated poor salmonid habitat quality with low habitat complexity with no large woody debris or instream cover. Heat Source model performance (Bias, RMSE, MARE, and NSE), compared to DTS iii observations, were all within the range of previous Heat Source applications. Heat Source modeling of reforestation of denuded legacy gravel bars from historic gold mining and areas of low vegetation in the study reach indicated that reforestation buffered daily maximum stream temperatures. Modeled channel restoration scenarios reduced the rate of heating (ºC /90 m) in the treatment area by a maximum of 34 %. Climate changescenarios were simulated with a uniform increase of air temperature by 2 °C, 4 °C, and 6 °C which warmed stream temperatures by 0.09 ºC / km per 2 ºC air temperature increase. Warming predicted by climate change was ameliorated with reforestation (0.11 ºC /km and 0.26 ºC per 2 ºC /km air temperature increase for partial and fully forested respectively).

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Modeling insights from distributed temperature sensing data
Created: April 1, 2018, 4:56 p.m.
Authors: Buck, C. R.

ABSTRACT:

Distributed Temperature Sensing (DTS) technology can collect abundant high resolution river temperature data over space and time to improve development and performance of modeled river temperatures. These data can also identify and quantify ther5 mal variability of micro-habitat that temperature modeling and standard temperature sampling do not capture. This allows researchers and practitioners to bracket uncertainty of daily maximum and minimum temperature that occurs in pools, side channels, or as a result of cool or warm inflows. This is demonstrated in a reach of the Shasta River in Northern California that receives irrigation runoff and inflow from small ground10 water seeps. This approach highlights the influence of air temperature on stream temperatures, and indicates that physically-based numerical models may under-represent this important stream temperature driver. This work suggests DTS datasets improve efforts to simulate stream temperatures and demonstrates the utility of DTS to improve model performance and enhance detailed evaluation of hydrologic processes.

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The shallow thermal regime of Devils Hole, Death Valley National Park
Created: April 1, 2018, 5 p.m.
Authors: Hausner, M. B.

ABSTRACT:

Devils Hole, a fracture in the carbonate aquifer underlying the Death Valley Regional Groundwater Flow system, is home to the only extant population of Devils Hole pupfish (Cyprinodon diabolis). Since 1995, the population of C. diabolis has shown an unexplained decline, and a number of hypotheses have been advanced to explain this. Here, we examine the thermal regime of Devils Hole and its influence on the pupfish population. We present a computational fluid dynamic (CFD) model of thermal convection on the shallow shelf of Devils Hole, which provides critical habitat for C. diabolis to spawn and forage for food. Driven by meteorological data collected at Devils Hole, the model is calibrated with temperature data recorded in the summer of 2010 and validated against temperatures observed on the shallow shelf between 1999 and 2001.The shallow shelf experiences both seasonal and diel variations in water temperature, and the model results reflect these changes. A sensitivity analysis shows that the water temperatures respond to relatively small changes in the ambient air temperature (on the order of 1 8C), and a review of local climate data shows that average annual air temperatures in the Mojave Desert have increased by up to 2 8C over the past 30 years. The CFD simulations and local climate data show that climate change may be partially responsible for the observed decline in the population of C. diabolis that began in 1995.

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ABSTRACT:

Distributed temperature sensing (DTS) is a fiber-optical method enabling simultaneous temperature measurements over long distances. Electrical resistance heating of the metallic components of the fiber-optic cable provides information on the thermal characteristics of the cable's environment, providing valuable insight into processes occurring in the surrounding medium, such as groundwater–surface water interactions, dam stability or soil moisture. Until now, heated applications required direct handling of the DTS instrument by a researcher, rendering long-term investigations in remote areas impractical due to the often difficult and time-consuming access to the field site. Remote control and automation of the DTS instrument and heating processes, however, resolve the issue with difficult access. The data can also be remotely accessed and stored on a central database. The power supply can be grid independent, although significant infrastructure investment is required here due to high power consumption during heated applications. Solar energy must be sufficient even in worst case scenarios, e.g. during long periods of intense cloud cover, to prevent system failure due to energy shortage. In combination with storage batteries and a low heating frequency, e.g. once per day or once per week (depending on the season and the solar radiation on site), issues of high power consumption may be resolved. Safety regulations dictate adequate shielding and ground-fault protection, to safeguard animals and humans from electricity and laser sources. In this paper the autonomous DTS system is presented to allow research with heated applications of DTS in remote areas for long-term investigations of temperature distributions in the environment.

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ABSTRACT:

The rate of groundwater flow has long been recognized as a critical control on solute transport in the subsurface. However, information about groundwater flux and its variability in space is rarely available, especially at the resolution required for investigations at sites of groundwater contamination. Recently, high‐resolution information about vertical variations in groundwater flux was obtained using fiber‐optic distributed temperature sensing technology to monitor the temperature response to active heating in a well. A series of vertical thermal profiles were acquired at a 1.4 cm resolution in a sand and gravel aquifer. These high‐resolution profiles, which display many of the same general features as hydraulic conductivity (K) profiles obtained using multiple techniques at the same well, provide new insights into site hydrostratigraphy. In particular, the near‐continuous profiles reveal the existence of thin zones of relatively high or low velocity that would be difficult to detect using other methods. These profiles also demonstrate that vertical variations in K may not be an accurate indicator of vertical variability in groundwater flux in highly heterogeneous aquifers.

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Thermal diffusivity of seasonal snow determined from temperature profiles
Created: April 1, 2018, 5:14 p.m.
Authors: Oldroyd, H. J.

ABSTRACT:

Thermal diffusivity of snow is an important thermodynamic property associated with key hydrological phenomena such as snow melt and heat and water vapor exchange with the atmosphere. Direct determination of snow thermal diffusivity requires coupled point measurements of thermal conductivity and density, which continually change due to snow metamorphism. Traditional methods for determining these two quantities are generally limited by temporal resolution. In this study we present a method to determine the thermal diffusivity of snow with high temporal resolution using snow temperature profile measurements. High resolution (between 2.5 and 10 cm at 1 min) temperature measurements from the seasonal snow pack at the Plaine-Morte glacier in Switzerland are used as initial conditions and Neumann (heat flux) boundary conditions to numerically solve the one-dimensional heat equation and iteratively optimize for thermal diffusivity. The implementation of Neumann boundary conditions and a t-test, ensuring statistical significance between solutions of varied thermal diffusivity, are important to help constrain thermal diffusivity such that spurious high and low values as seen with Dirichlet (temperature) boundary conditions are reduced. The results show that time resolved thermal diffusivity can be determined from temperature measurements of seasonal snow and support density-based empirical parameterizations for thermal conductivity.

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ABSTRACT:

We show how fully distributed space‐time measurements with Fiber‐Optic Distributed Temperature Sensing (FO‐DTS) can be used to investigate groundwater flow and heat transport in fractured media. Heat injection experiments are combined with temperature measurements along fiber‐optic cables installed in boreholes. Thermal dilution tests are shown to enable detection of cross‐flowing fractures and quantification of the cross flow rate. A cross borehole thermal tracer test is then analyzed to identify fracture zones that are in hydraulic connection between boreholes and to estimate spatially distributed temperature breakthrough in each fracture zone. This provides a significant improvement compared to classical tracer tests, for which concentration data are usually integrated over the whole abstraction borehole. However, despite providing some complementary results, we find that the main contributive fracture for heat transport is different to that for a solute tracer.

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ABSTRACT:

Increasing numbers in interdisciplinary applications of Fiber-optic DistributedTemperature Sensing (FO-DTS) call for a quantitative assessment of the limitations anduncertainties of this new technology. This study conducts controlled laboratory experimentsto analyze the qualitative (signal size and location) and quantitative (signal intensity)accuracies of FO-DTS surveys of temperature signals higher and lower than ambienttemperature, ranging from well above to critically below the FO-DTS sampling interval.Our results reveal that qualitative and quantitative accuracies of FO-DTS measuredtemperatures critically decline with decreasing signal size, in particular for signals near thespatial sampling interval. Decreasing detection accuracy risks the masking of realtemperature variation in highly dynamic systems. The resulting potential ambiguity ofinterpretations of signal size, intensity, and absolute location will have to be considered infuture experimental design and interpretation of FO-DTS surveys.

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Intrusion of warm surface water beneath the McMurdo Ice Shelf, Antarctica
Created: April 1, 2018, 5:25 p.m.
Authors: Stern, A.

ABSTRACT:

A 6 month temperature record collected below McMurdo Ice Shelf in 2011–2012 shows the temporal and spatial structure of the summertime warm water signal that penetrates beneath the ice shelf. The strength and duration of the warm water intrusion suggest an annual melt rate at Windless Bight of 0.71 m/yr. A Ross Sea numerical model demonstrates a seasonal warm water pathway leading from the west side of the Ross Sea Polynya (RSP) toward McMurdo Sound. The warm water enters McMurdo Sound, subducts beneath the ice shelf and causes accelerated summer melting. Temperature data were recorded using Distributed Temperature Sensing fiber optics, which gives a vertical temperature profile at a 1 m vertical resolution. This study constitutes one of the first successful implementations of this technology in Polar Regions.

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ABSTRACT:

Monitoring of ice-shelf and sub-ice-shelf ocean temperatures represents an important component in understanding ice-sheet stability. Continuous monitoring is challenging due to difficult surface access, difficulties in penetrating the ice shelf, and the need for long-term operation of nonrecoverable sensors. We aim to develop rapid lightweight drilling and near-continuous fiber-optic temperature-monitoring methods to meet these challenges. During November 2011, two instrumented moorings were installed within and below the McMurdo Ice Shelf (a sub-region of the Ross Ice Shelf, Antarctica) at Windless Bight. We used a combination of ice coring for the upper portion of each shelf borehole and hot-point drilling for penetration into the ocean. The boreholes provided temporary access to the ice-shelf cavity, into which distributed temperature sensing (DTS) fiber-optic cables and conventional pressure/temperature transducers were installed. The DTS moorings provided nearcontinuous (in time and depth) observations of ice and ocean temperatures to a depth of almost 800 m beneath the ice-shelf surface. Data received document the presence of near-freezing water throughout the cavity from November through January, followed by an influx of warmer water reaching 150 m beneath the ice-shelf base during February and March. The observations demonstrate prospects for achieving much higher spatial sampling of temperature than more conventional oceanographic moorings.

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ABSTRACT:

Surface and groundwater discharges and contaminant fluxes can vary with time and space depending upon the hydrogeological processes and geological setting of the area of interest. This study examined a ~300-m-long, channelized reach of a first-order perennial stream, Little Bayou Creek, in the Coastal Plain of far western Kentucky during the period October 2010–February 2012. Along the study reach, springs discharge groundwater contaminated by the chlorinated organic compound trichloroethene (TCE) and radionuclide technetium-99 (99Tc) released as a result of past activities at the U.S. Department of Energy’s Paducah Gaseous Diffusion Plant. The study addressed variability in groundwater discharge patterns and contaminant concentrations at various timescales (seasonal, annual, and decadal) and the extent to which the discharge sites are spatially persistent. Understanding patterns of groundwater discharge along a stream can be important for assessing the fate and transport of aqueous contaminants.

Groundwater discharge was estimated during baseflow conditions using different mass-balance approaches, including velocity-area and dye-dilution gauging. Discharge fluctuated seasonally but typically increased downstream, indicating the entire study reach to be gaining throughout the year. Discharge rates of individual springs also fluctuated seasonally. Tracer test data were utilized to model flow and transient storage along the reach using the USGS software OTIS-P. Cross-sectional area determined from OTIS-P was similar to that measured by velocity-area gauging. Reach area-normalized discharge fluxes were comparable to values determined by Darcy’s law calculations from a pair of monitoring wells at the downstream end of the study reach. Temperature data acquired from probing along grids in winter and summer, from fiber-optic sensing along the reach in autumn, and from data-loggers and manual measurements in springs were used to delineate focused discharge locations. Comparison of temperature-probing results with prior studies indicated that locations of some springs persisted over a decade, whereas other springs emerged and disappeared. Because the stream is located in unlithified sediments, discharge rates of springs appear to fluctuate with soil piping and collapse along joints in fractured clay. Contaminant concentrations in springs decreased downstream along the reach and were lower than observed during September 1999 – May 2001. The continued occurrence of dissolved oxygen and the absence of TCE daughter products in springs suggest that the decrease in TCE concentrations resulted from the installation of upgradient extraction wells, rather than from intrinsic reductive degradation.

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ABSTRACT:

Devils Hole, a groundwater-filled fracture in the carbonate aquifer of the southern Nevada Mojave Desert, represents a unique ecohydrological setting, as home to the only extant population of Cyprinodon diabolis, the endangered Devils Hole pupfish. Using water column temperatures collected with a fiber-optic distributed temperature sensor (DTS) during four field campaigns in 2009, evidence of deep circulation and nutrient export are, for the first time, documented. The DTS was deployed to measure vertical temperature profiles in the system, and the raw data returned were postprocessed to refine the calibration beyond the precision of the instrument’s native calibration routines. Calibrated temperature data serve as a tracer for water movement and reveal a seasonal pattern of convective mixing that is supported by numerical simulations of the system. The periodic presence of divers in the water is considered, and their impacts on the temperature profiles are examined and found to be minimal. The seasonal mixing cycle may deplete the pupfish’s food supplies when nutrients are at their scarcest. The spatial and temporal scales of the DTS observations make it possible to observe temperature gradients on the order of 0.001C m1 , revealing phenomena that would have been lost in instrument noise and uncertainty.

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Active Thermal Tracer Tests for Improved Hydrostratigraphic Characterization
Created: April 1, 2018, 5:57 p.m.
Authors: Leaf, A. T.

ABSTRACT:

Subsurface heterogeneity in hydraulic properties and processes is a fundamental challenge in hydrogeology. We have developed an improved method of borehole dilution testing for hydrostratigraphic characterization, in which distributed temperature sensing (DTS) is used to monitor advective heat movement. DTS offers many advantages over conventional technologies including response times in the order of seconds rather than minutes, the ability to profile temperature synoptically in a well without disturbing the fluid column, sensitivity to a wider range of flow rates than conventional spinner and heat pulse flow meters, and the ease of interpretation. Open‐well thermal dilution tests in two multiaquifer wells near Madison, Wisconsin, provided detailed information on the borehole flow regimes, including flow rates and the locations of inflows from both fractures and porous media. The results led to an enhanced understanding of flow in a hydrostratigraphic unit previously conceptualized as homogenous and isotropic.

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ABSTRACT:

Studies of forest meteorology are often conducted at the stand level, but few studies examine temperature heterogeneity within stands. Differences in canopy structure, whether caused by species composition or disturbances, introduce variation in the amount of light reaching the forest floor, which in turn introduces variation in forest floor temperatures. Furthermore, in temperate latitudes, canopy openings cast light on the forest floor in complex patterns depending on the path of the sun throughout one day and throughout the season. We installed two temperature measurement devices in control, gap, and thinning treatments to capture both the time structure and spatial variability of forest floor temperature. We compared air temperatures measured by meteorological stations to spatially continuous ground surface temperatures measured along 760 m of fiber-optic cable. Using the principle of Raman spectra distributed temperature sensing, we inferred temperature at 1 m intervals along the fiber-optic cable every 30 minutes for 42 days in May – June 2010. In regenerating secondary forests with generally intact canopies, temperatures were spatially correlated throughout the day and night. In thinned forests or in gaps, ground surface temperatures were spatially correlated at night, but spatially heterogeneous during the day, suggesting that meter-scale measurements may be required to adequately characterize these environments. Understory plant species richness was 50% lower where higher temperatures were measured. We also modeled light transmission through the overstory with tRAYci and found that understory plant species richness was highest at 10% of above-canopy light and lower at both lower and higher light levels.

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ABSTRACT:

Characterization of groundwater-surface water exchange is essential for improving understanding of contaminant transport between aquifers and rivers. Fiber-optic distributed temperature sensing (FODTS) provides rich spatiotemporal datasets for quantitative and qualitative analysis of groundwatersurface water exchange. We demonstrate how time-frequency analysis of FODTS and synchronous river stage time series from the Columbia River adjacent to the Hanford 300-Area, Richland, Washington, provides spatial information on the strength of stage-driven exchange of uranium contaminated groundwater in response to subsurface heterogeneity. Although used in previous studies, the stage-temperature correlation coefficient proved an unreliable indicator of the stage-driven forcing on groundwater discharge in the presence of other factors influencing river water temperature. In contrast, S-transform analysis of the stage and FODTS data definitively identifies the spatial distribution of discharge zones and provided information on the dominant forcing periods (≥2 d) of the complex dam operations driving stage fluctuations, and hence groundwater-surface water exchange at the 300-Area.

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Heated Distributed Temperature Sensing for Field Scale Soil Moisture Monitoring
Created: April 1, 2018, 6:12 p.m.
Authors: Striegl, A. M.

ABSTRACT:

Characterizing both spatial and temporal soil moisture (θ) dynamics at site scales is difficult with existing technologies. To address this shortcoming, we developed a distributed soil moisture sensing system that employs a distributed temperature sensing system to monitor thermal response at 2 m intervals along the length of a buried cable which is subjected to heat pulses. The cable temperature response to heating, which is strongly dependent on soil moisture, was empirically related to colocated, dielectric-based θ measurements at three locations. Spatially distributed, and temporally continuous estimates of θ were obtained in dry conditions (θ ≤ 0.31) using this technology (root mean square error [RMSE] = 0.016), but insensitivity of the instrument response curve adversely affected accuracy under wet conditions (RMSE = 0.050).

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ABSTRACT:

We present a novel approach based on fibre-optic distributed temperature sensing (DTS) to measure the two-dimensional thermal structure of the surface layer at high resolution (0.25m, ≈0.5 Hz). Air temperature observations obtained from a vertically-oriented fibre-optics array of approximate dimensions 8m×8m and sonic anemometer data from two levels were collected over a short grass field located in the flat bottom of a wide valley with moderate surface heterogeneity. The objectives of the study were to evaluate the potential of the DTS technique to study small-scale processes in the surface layer over a wide range of atmospheric stability, and to analyze the space–time dynamics of transient cold-air pools in the calm boundary layer. The time response and precision of the fibre-based temperatures were adequate to resolve individual sub-metre sized turbulent and non-turbulent structures, of time scales of seconds, in the convective, neutral, and stable surface layer. Meaningful sensible heat fluxes were computed using the eddy-covariance technique when combined with vertical wind observations. We present a framework that determines the optimal environmental conditions for applying the fibre-optics technique in the surface layer and identifies areas for potentially significant improvements of the DTS performance. The top of the transient cold-air pool was highly non-stationary indicating a superposition of perturbations of different time and length scales. Vertical eddy scales in the strongly stratified transient cold-air pool derived from the DTS data agreed well with the buoyancy length scale computed using the vertical velocity variance and the Brunt–Vaisala frequency, while scales for weak stratification disagreed. The high-resolution DTS technique opens a new window into spatially sampling geophysical fluid flows including turbulent energy exchange.

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Double-Ended Calibration of Fiber-Optic Raman Spectra Distributed Temperature Sensing Data
Created: April 1, 2018, 6:18 p.m.
Authors: van de Giesen, N.

ABSTRACT:

Over the past five years, Distributed Temperature Sensing (DTS) along fiber optic cables using Raman backscattering has become an important tool in the environmental sciences. Many environmental applications of DTS demand very accurate temperature measurements, with typical RMSE < 0.1 K. The aim of this paper is to describe and clarify the advantages and disadvantages of double-ended calibration to achieve such accuracy under field conditions. By measuring backscatter from both ends of the fiber optic cable, one can redress the effects of differential attenuation, as caused by bends, splices, and connectors. The methodological principles behind the double-ended calibration are presented, together with a set of practical considerations for field deployment. The results from a field experiment are presented, which show that with double-ended calibration good accuracies can be attained in the field.

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Distributed!temperature!sensing!(DTS)!as!a!hydrostratigraphic!characterization!tool
Created: April 1, 2018, 6:22 p.m.
Authors: Bahr, J. M.

ABSTRACT:

Subsurface heterogeneity in hydraulic properties and processes is a fundamental challenge in hydrogeology. Most hydrogeologic problems are complicated by uncertainty in permeability, which is often difficult or impossible to fully characterize. The usefulness of heat as a tracer has been limited by thermometry that only records temporal changes in temperature at a single fixed or moving point. Distributed temperature sensing (DTS) is a powerful new method that allows for the nearly continuous measurement of temperature in time and space along fiber-optic cables. The fine spatial and temporal monitoring ability of DTS is creating new and unprecedented opportunities to study hydraulic heterogeneity at a wide range of scales. Despite numerous recent applications of DTS applications in surface water investigations, down-hole uses in hydrogeology have been limited. Recent studies on the Sandstone Aquifer system of Wisconsin have shown preferential flow through laterally continuous bedding plane
fractures to be a defining characteristic of sandstone units that were traditionally assumed to be homogeneous and isotropic. The implication of these findings is that more detailed characterization efforts are necessary to adequately assess flow and transport problems in these units.

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ABSTRACT:

Degassing of CO2 on the flanks of the active Erebus volcano is thought to occur mainly through fumarolic ice caves (FIC) and associated fumarolic ice towers. There is alsom minor CO2 degassing from isolated areas of warm ground. The mechanism supplying heat and CO2 gas into the FIC is poorly understood. To investigate this system, a fiber optic distributed temperature sensing (DTS) system was deployed in a FIC to obtain temperature measurements every meter. The DTS data reveal that localized gas vents (GV) supply heat to the FIC air mass and are an important component of the FIC microclimate. FIC temperature is anti‐correlated with local atmospheric pressure, indicating barometric pumping of the GV. These results enable the use of FIC temperature as a proxy for flank degassing rate on Erebus, and represent the first application of DTS for monitoring an active volcano.

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Calibrating Single-Ended Fiber-Optic Raman Spectra Distributed Temperature Sensing Data
Created: April 1, 2018, 6:29 p.m.
Authors: Hausner, M. B.

ABSTRACT:

Hydrologic research is a very demanding application of fiber-optic distributed temperature sensing (DTS) in terms of precision, accuracy and calibration. The physics behind the most frequently used DTS instruments are considered as they apply to four calibration methods for single-ended DTS installations. The new methods presented are more accurate than the instrument-calibrated data, achieving accuracies on the order of tenths of a degree root mean square error (RMSE) and mean bias. Effects of localized non-uniformities that violate the assumptions of single-ended calibration data are explored and quantified. Experimental design considerations such as selection of integration times or selection of the length of the reference sections are discussed, and the impacts of these considerations on calibrated temperatures are explored in two case studies.

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ABSTRACT:

A new method for measuring air temperature profiles in the atmospheric boundary layer at high spatial and temporal resolution is presented. The measurements are based on Raman scattering distributed temperature sensing (DTS) with a fiber optic cable attached to a tethered balloon. These data were used to estimate the height of the stable nocturnal boundary layer. The experiment was successfully
deployed during a two-day campaign in September 2009, providing evidence that DTS is well suited for this atmospheric application. Observed stable temperature profiles exhibit an exponential shape confirming similarity concepts of the temperature inversion close to the surface. The atmospheric mixing height (MH) was estimated to vary between 5 m and 50 m as a result of the nocturnal boundary layer evolution. This value is in good agreement with the MH derived from concurrent Radon-222 (222Rn) measurements and in previous studies.

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ABSTRACT:

In shallow thermohaline-driven lakes it is important to measure temperature on fine spatial and temporal scales to detect stratification or different hydrodynamic regimes. Raman spectra distributed temperature sensing (DTS) is an approach available to provide high spatial and temporal temperature resolution. A vertical high-resolution DTS system was constructed to overcome the problems of typical methods used in the past, i.e., without disturbing the water column, and with resistance to corrosive environments. This paper describes a method to quantitatively assess accuracy, precision and other limitations of DTS systems tom fully utilize the capacity of this technology, with a focus on vertical high-resolution to measure temperatures in shallow thermohaline environments. It also presents a new method to manually calibrate temperatures along the optical fiber achieving significant improved resolution. The vertical highresolution DTS system is used to monitor the thermal behavior of a salt-gradient solar pond, which is an engineered shallow thermohaline system that allows collection and storage of solar energy for a long period of time. The vertical high-resolution DTS system monitors the temperature profile each 1.1 cm vertically and in time averages as small as 10 s. Temperature resolution as low as 0.035 ◦C is obtained when the data are collected at 5-min intervals.

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ABSTRACT:

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Evolution of superficial lake water temperature profile under diurnal radiative forcing
Created: April 1, 2018, 6:48 p.m.
Authors: Vercauteren, N.

ABSTRACT:

In lentic water bodies, such as lakes, the water temperature near the surface typically increases during the day, and decreases during the night as a consequence of the diurnal radiative forcing (solar and infrared radiation). These temperature variations penetrate vertically into the water, transported mainly by heat conduction enhanced by eddy diffusion, which may vary due to atmospheric conditions, surface wave breaking, and internal dynamics of the water body. These two processes can be described in terms of an effective thermal diffusivity, which can be experimentally estimated. However, the transparency of the water (depending on turbidity) also allows solar radiation to penetrate below the surface into the water body, where it is locally absorbed (either by the water or by the deployed sensors). This process makes the estimation of effective thermal diffusivity from experimental water temperature profiles more difficult. In this study, we analyze water temperature profiles in a lake with the aim of showing that assessment of the role played by radiative forcing is necessary to estimate the effective thermal diffusivity. To this end we investigate diurnal water temperature fluctuations with depth. We try to quantify the effect of locally absorbed radiation and assess the impact of atmospheric conditions (wind speed, net radiation) on the estimation of the thermal diffusivity. The whole analysis is based on the results of fiber optic
distributed temperature sensing, which allows unprecedented high spatial resolution measurements (4 mm) of the temperature profile in the water and near the water surface.

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ABSTRACT:

Interest in groundwater (GW)-surface water (SW) interactions has grown steadily over the last two decades. New regulations such as the EU Water Framework Directive (WFD) now call for a sustainable management of coupled ground- and surface water resources and linked ecosystems. Embracing this mandate requires new interdisciplinary research on GW-SW systems that addresses the linkages between hydrology, biogeochemistry and ecology at nested scales and specifically accounts for small-scale spatial and temporal patterns of GW-SW exchange. Methods to assess these patterns such as the use of natural tracers (e.g. heat) and integrated surface-subsurface numerical models have been refined and enhanced significantly in recent years and have improved our understanding of processes and dynamics. Numerical models are increasingly used to explore hypotheses and to develop new conceptual models of GW-SW interactions. New technologies like distributed temperature sensing (DTS) allow an assessment of process dynamics at unprecedented spatial and temporal resolution. These developments are reflected in the contributions to this Special Issue on GW-SW interactions. However, challenges remain in transferring process understanding across scales.

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Solar radiative heating of fiber‐optic cables used to monitor temperatures in water
Created: April 1, 2018, 7:03 p.m.
Authors: Neilson, B. T.

ABSTRACT:

In recent years, applications of distributed temperature sensing (DTS) have increased in number and diversity. Because fiber‐optic cables used for DTS are typically sheathed in dark UV‐resistant materials, the question arises as to how shortwave solar radiation penetrating a water column influences the accuracy of absolute DTS‐derived temperatures in aquatic applications. To quantify these effects, we completed a modeling effort that accounts for the effects of radiation and convection on a submersed cable to predict when solar heating may be important. Results indicate that for cables installed at shallow depths in clear, low‐velocity water bodies, measurable heating of the cable is likely during peak solar radiation. However, at higher velocities, increased turbidity and/or greater depths, the effects of solar heating are immeasurable. A field study illustrated the effects of solar radiation by installing two types of fiber‐optic cable at multiple water depths (from 0.05 to 0.8 m) in the center and along the sidewall of a trapezoidal canal. Thermistors were installed at similar depths and shielded from solar radiation to record absolute water temperatures. During peak radiation, thermistor data showed small temperature differences (∼0.003°C–0.04°C) between depths suggesting minor thermal stratification in the canal center. DTS data from cables at these same depths show differences of 0.01°C–0.17°C. The DTS differences cannot be explained by stratification alone and are likely evidence of additional heating from solar radiation. Sidewall thermistor strings also recorded stratification. However, corresponding DTS data suggested that bed conduction overwhelmed the effects of solar radiation.

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Feasibility of soil moisture estimation using passive distributed temperature sensing
Created: April 1, 2018, 7:08 p.m.
Authors: Steele-Dunn, S. C.

ABSTRACT:

Through its role in the energy and water balances at the land surface, soil moisture is a key state variable in surface hydrology and land‐atmosphere interactions. Point observations of soil moisture are easy to make using established methods such as time domain reflectometry and gravimetric sampling. However, monitoring large‐scale variability with these techniques is logistically and economically infeasible. Here passive soil distributed temperature sensing (DTS) will be introduced as an experimental method of measuring soil moisture on the basis of DTS. Several fiber‐optic cables in a vertical profile are used as thermal sensors, measuring propagation of temperature changes due to the diurnal cycle. Current technology allows these cables to be in excess of 10 km in length, and DTS equipment allows measurement of temperatures every 1 m. The passive soil DTS concept is based on the fact that soil moisture influences soil thermal properties. Therefore, observing temperature dynamics can yield information on changes in soil moisture content. Results from this preliminary study demonstrate that passive soil DTS can detect changes in thermal properties. Deriving soil moisture is complicated by the uncertainty and nonuniqueness in the relationship between thermal conductivity and soil moisture. A numerical simulation indicates that the accuracy could be improved if the depth of the cables was known with greater certainty.

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Deep Underground Instrumentation And Monitoring
Created: April 1, 2018, 7:12 p.m.
Authors: Wang, H. F.

ABSTRACT:

The structural integrity of deep, large underground facilities such as tunnels, mines, pumped storage facilities, and physics laboratories requires the ability to predict rock mass stability under loading to ensure the safety of human occupants and the longevity of the underground space. Deformation occurs over time scales that range from milliseconds to decades and spatial scales that range from millimeters to facility scale. Beginning with design, prediction is typically based on finite element models using available or estimated properties. As with most geotechnical problems, much of the difficulty of prediction lies in the inability to sufficiently characterize the rock properties, especially discontinuities. As a consequence, semi-quantitative measures, such as Rock Mass Rating (RMR) or the Hoek-Brown Geological Structure Index (GSI) [1], are used to characterize the rock mass together with empirical charts for design criteria such as rock bolt spacing for ground control. During and following construction, validating model predictions is necessary to assess their performance. Parameter adjustment, or even the physics incorporated within the model, can be made using back analysis. This monitoring should be a continuous or periodic process over the life of the facility. For civil structures, the post-construction era will be measured in decades. With the inherent uncertainties and high stresses associated with the deep underground environment, the potential for rock failure must always be borne in mind. Mitigating the risk is prudent, but formal cost-benefit analysis may be precluded by the uncertainties. Keeping abreast of the condition of the facility through Structural Health Monitoring (SHM) is gaining acceptance for underground construction [2]. One reason for the growth in research in monitoring is that maturing technologies, like fiber-optic sensors and associated instrumentation, can collect data that were not previously achievable. They are robust and geometrically flexible, possess long-term stability, are cost effective, and extend coverage in spatial extent with improved resolution or provide data at a higher sampling rate. In addition to fiber-optic technology, a host of new technologies with potential for underground geotechnical applications exist, including LIDAR, wireless “smart dust”, piezoelectric sensors, and high resolution electrical and seismic imaging [3; 4; 5; 6; 7]. The subject of this paper is mainly to describe preliminary experiments, future needs, and instrumentation and monitoring plans of the authors' research activities in the 2400-meter Deep Underground Science and Engineering Laboratory (DUSEL) in the Black Hills of South Dakota, USA, where fiber-optic sensors and water-level tiltmeter arrays have been installed.

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ABSTRACT:

The exchange of groundwater and surface water (GW‐SW), including dissolved constituents and energy, represents a critical yet challenging characterization problem for hydrogeologists and stream ecologists. Here we describe the use of a suite of high spatial resolution remote sensing techniques, collected using a small unmanned aircraft system (sUAS), to provide novel and complementary data to analyze GW‐SW exchange. sUAS provided centimeter‐scale resolution topography and water surface elevations, which are often drivers of exchange along the river corridor. Additionally, sUAS‐based vegetation imagery, vegetation‐top elevation, and normalized difference vegetation index mapping indicated GW‐SW exchange patterns that are difficult to characterize from the land surface and may not be resolved from coarser satellite‐based imagery. We combined these data with estimates of sediment hydraulic conductivity to provide a direct estimate of GW “shortcutting” through meander necks, which was corroborated by temperature data at the riverbed interface.

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Analysis of Radar and ADS-B Influences on Aircraft Detect and Avoid (DAA) Systems
Created: April 1, 2018, 7:22 p.m.
Authors: Semke, W.

ABSTRACT:

Detect and Avoid (DAA) systems are complex communication and locational technologies comprising multiple independent components. DAA technologies support communications between ground-based and space-based operations with aircraft. Both manned and unmanned aircraft systems (UAS) rely on DAA communication and location technologies for safe flight operations. We examined the occurrence and duration of communication losses between radar and automatic dependent surveillance–broadcast (ADS-B) systems with aircraft operating in proximate airspace using data collected during actual flight operations. Our objectives were to identify the number and duration of communication losses for both radar and ADS-B systems that occurred within a discrete time period. We also investigated whether other unique communication behavior and anomalies were occurring, such as reported elevation deviations. We found that loss of communication with both radar and ADS-B systems does occur, with variation in the length of communication losses. We also discovered that other unexpected behaviors were occurring with communications. Although our data were gathered from manned aircraft, there are also implications for UAS that are operating within active airspaces. We are unaware of any previously published work on occurrence and duration of communication losses between radar and ADS-B systems.

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Automated Extraction of Forest Road Network Geometry from Aerial LiDAR
Created: April 1, 2018, 7:28 p.m.
Authors: Storm, J. C.

ABSTRACT:

We developed an algorithm that was designed to create a spatial database of a forested transportation network using aerial LiDAR. The algorithm uses two main attributes, LiDAR intensity values and ground return density. The road extraction process was developed using aerial LiDAR from McDonald-Dunn Research Forest near Corvallis, Oregon, U.S.A. The road extraction process requires X, Y, Z coordinates, intensity values, canopy type, and the maximum road grade. To compare the results of the process, nine road segments were field surveyed with terrestrial LiDAR. The result of the road extraction process resulted in 80% true positives, 34% false positives, 20% false negatives, and 38% true negatives in identifying forest roads. The average absolute value difference in the road width between the two data sets were 1.1m, while the cut/fill slope differences were minimal (> 4%) and the difference in road cross slope was two percent. These results were comparable with other published studies that examined differences between LiDAR measurements and field measurements.

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Identification of Passaic River Groundwater-Surface Water Exchange
Created: July 6, 2018, 10:36 p.m.
Authors: Selker, Frank · Huff, Julie

ABSTRACT:

Identifying where groundwater-surface water exchange occurs along the lower 8 miles of river bed of the Passaic River, NJ utilizing armoured fiber optic cable and Silixa XT-DTS from June 11 - August 8, 2018.

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ABSTRACT:

The current scope involves three FO-DTS deployments, each 1km in length and for 5 days each. The site we are working on would like to evaluate groundwater discharge from the site into the river downgrade to facilitate discrete porewater sampling and evaluate potential plume migration. Previous GSI studies have been conducted here; however, due to recent landscape changes a comprehensive seepage survey is desired.

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ABSTRACT:

The upper Delaware River, a dam-regulated river forming the boundary between New York and Pennsylvania, is home to numerous native species of mussels, including the endangered dwarf wedgemussel, a species that is susceptible to temperature changes more so than other native species. Due to the nature of human water management practices, low flow events can be accentuated, resulting in increased stream temperature [Galbraith et al., 2012; Maloney et al., 2012]. Thermal refugia for aquatic species is vital for survival during these highly variable or extreme temperature conditions [Boulton et al., 1998]. Groundwater-surface water interactions at both diffuse and discrete locations can provide areas in which these endangered mussels can not only survive but also thrive. As part of an ongoing USGS project, four unique high-resolution temperature data collection techniques have been deployed at three locations. These techniques include fiber-optic distributed temperature sensing (FO-DTS), drone-mounted thermal imaging, boat-mounted real-time thermal mapping, and individual thermistors. All of these techniques are being used in a qualitative way with the goal to identify locations of groundwater discharge that provide aquatic species refuge during extreme temperature events as well as to build temperature models that will be incorporated into a larger riverine decision support system to help resource managers. While this ongoing study incorporates FO-DTS in an established manner, there is a unique opportunity to deploy a physical, vertically paired fiber-optic cable at one of the three sites. Located in Equinunk, PA, this well-characterized field site has been instrumented with vertical high-resolution temperature sensors (FO-DTS wrapped around a post) and hand-held
thermal imaging, providing point measurements of flux [Briggs et al., 2013]. Ecological surveys have also identified dwarf wedgemussles along the bank of this stream reach in locations of groundwater upwelling. Although numerous studies have deployed paired fiber-optic cable, both in physical laboratory experiments [Mamer and Lowry, 2013] and in field settings [Becker et al., 2013; Mawer et al., 2016], these deployments bury the cables vertically one over the other, resulting in differential spacing both horizontally and vertically, leading to erroneous results. By physically pairing two fiber-optic cables, FO-DTS transitions to a quantitative tool capable of providing thousands of flux measurements at a fine spatial and temporal scale. The act of physically connecting the cables removes this uncertainty.

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ABSTRACT:

We are performing an Aquifer Storage and Recovery injection test in a newly installed test well. A nearby well with a relatively long well screen interval will be used to sample recovered groundwater to assess water quality. The DTS cable will be installed in the nearby observation to determine the best depth to place a sampling pump for performing the water quality tests and to better evaluate potential vertical variations in relative aquifer transmissivity during the test. The DTS cable will be deployed in a locked environment at the City of Sonoma wellsite.

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ABSTRACT:

The use of tile drainage is documented as far back as 200 B. C. and continues to be used in poorly drained agricultural regions throughout the world. Recent increases in annual precipitation throughout the mid-western United States, the potential for future regulation of tile, and more efficient installation methods for plastic tile have accelerated tile installation across the region. While good for crop production, the eco-hydrologic impacts of this modification have been shown to adversely affect natural drainage networks. Knowing the location of tile drain networks is essential to developing groundwater and surface water models. The geometry of tile networks installed decades ago has often been lost with time or was never well documented in the first place. Previous work has recognized that tiles can be observed for certain soil types in visible remote sensing data due to changes in soil albedo. The soil surface directly above the tile appears to have a lower soil moisture content due to strong water table gradients adjacent to tiles, causing a detectable color contrast at the surface. In this work, small Unmanned Aerial Systems (sUAS) were used to collect high resolution visible and thermal data to map tile drain patterns. Within less than 96 hours of a 12 mm rain event, a total of approximately 60 hectares of sUAS thermal and RGB data were acquired at two different locations at the Intensively Managed Lands Critical Zone Observatory in Illinois. Selected thermal images were co-registered with RGB images at known tile locations. The thermal imagery showed limited evidence of thermal contrast related to the tile, however, it is possible that a contrast could have been detected sooner after the rain event when greater thermal contrasts due to lower soil moisture proximal to tile would be expected. The RGB data, however, elucidated the tile entirely at one site and provided traces of the tile at the other site. These results illustrate the importance of the timing of sUAS data collection with respect to the precipitation event. Ongoing related work focusing on laboratory and numerical experiments to better quantify feedbacks between albedo, soil moisture, and heat transfer will help predict the optimal timing of data collection for applications such as tile mapping.

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SAVANT: Stable Atmospheric Variability ANd Transport
Created: Jan. 2, 2019, 10:23 p.m.
Authors: April Hiscox · Junming Wang · David Kristovich

ABSTRACT:

Stable boundary layers are still a relatively problematic component of atmospheric modeling, despite their frequent occurrence. While general agreement exists that MO similarity is not applicable in the SBL due to the non-homogeneous, non-stationary flow, no universal organizing theory for the surface SBL has been presented. This poses a problem when examining aerosol movement as a function of atmospheric dynamics. It is known that stable air stratification results in katabatic downslope winds, even in very shallow topographic airsheds. These downslope winds can converge with background flow, and it is hypothesized that this convergence provides a starting point for specific events, such as internal gravity waves. Even though the stable boundary layer is normally shallow, internal gravity waves can propagate at an angle from the horizontal plane, and modify local shear, thus generating periodic turbulent mixing in space. Some studies have measured converging background and drainage flows in mountain areas, however, few studies have examined this in less dramatic, but more common, topographic areas. We are conducting a measurement campaign to address these open issues.

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Measurement of internal seiche in Lake Chelan, WA
Created: Jan. 2, 2019, 10:48 p.m.
Authors: Phil Long · CTEMPs OSU-UNR

ABSTRACT:

The large internal seiche of the Lucerne Basin of Lake Chelan was described in Pelletier et al., 1989, in short, the rocking back and forth of the deep cold water in the Lucerne Basin. The data for this study was collected in 1986 and 1987 and showed an extreme internal seiche. During the summer of 1987 the amplitude of the rocking of the deep cold water was as much as 70 m and the period was approximately 3 days. The main goals of this study were to a) investigate the internal seiche in more detail than was possible in the 1980’s and b) determine how the seiche interacted with the sill between the Lucerne Basin and the Wapato Basin.

This study is significant to water quality of Lake Chelan in two ways. 1) Without knowing the status of the internal seiche under summer conditions, it is difficult to know the source of waters being sampled, the deep cold water versus the shallow warm water in the lake. Each of these waters typically exhibit different water quality signatures. 2) The interaction of the internal seiche with the lake bottom likely influences the transport of fine sediment, sediment distribution and water clarity in the vicinity of the narrows of Lake Chelan. Without knowledge of the seiche dynamics it will be difficult to interpret secchi depths and related water quality parameters in this part of the lake.

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Of Cones & Eddies: Toward building the first 3-dimensional fiber-optic flow sensor
Created: Jan. 3, 2019, midnight
Authors: Karl Lapo · Anita Freundorfer · Lena Pfister · Johann Schneider · Christoph Thomas

ABSTRACT:

Goal: Develop techniques for observing 3D, high resolution atmospheric motions during stably stratified
conditions.
Missing Physics: The need for a full 3D sensor
1) Fundamental mismatch between scales of variability in wind and temperature break observation assumptions
2) Stability and wind speed alone can not describe the strength of mixing during weak wind conditions
3) Spatial heterogeneity in both temperature and wind fields at varying scales

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Wind speed from actively heated fiber optic cables
Created: Jan. 2, 2019, 11:14 p.m.
Authors: Justus van Ramshorst

ABSTRACT:

Near-surface wind speed is typically only measured by point observations. The so-called Actively Heated Fiber-Optic (AHFO) technique, however, has the potential to provide high-resolution distributed observations, allowing for better understanding of different processes. However, before it can be widely used, its performance needs to be tested in a range of settings. Therefore, in this work, experimental results on this novel observational wind-probing technique are presented. We utilized a controlled wind-tunnel setup to assess both the accuracy and the precision of AHFO as well as its potential for outdoor atmospheric operation. The technique allows for wind speed characterization with a spatial resolution of 0.3 m on a 1 s time scale. The flow in the wind tunnel is varied in a controlled manner, such that the mean wind, ranges between 1 and 17 m/s. Comparison of the AHFO measurements with observations from a sonic anemometer shows a high overall correlation, ranging from 0.94-0.99. Also, both precision and accuracy are greater than 95 %. As such, it is concluded that the AHFO has potential to be employed as an outdoor observational technique in addition to existing techniques. In particular, it allows for characterization of spatial varying fields of mean wind in complex terrain, such as in canopy flows or in sloping terrain. In the future the technique could be combined with regular Distributed Temperature Sensing (DTS) for turbulent heat flux estimation in micrometeorological/hydrological applications.

Raw DTS project data will be available in 2020 by contacting ctemps@unr.edu.

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