R script to calculate daily PAR from solar radiation data
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|Created:||Jun 03, 2016 at 2:32 p.m.|
|Last updated:|| Jun 11, 2016 at 2:05 p.m.
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Generating estimates of daily reference photosynthetically Active Radiation (PAR). We show the procedure to generate estimates of daily reference PAR using solar radiation data. The input for the R script (CalculateDailyPAR.R) is a raw time series of hourly solar radiation (stored in variable ‘ws’) that for our case was obtained from the CIMIS website (station id: 105) [California Department of Water Resources, 2015]. The script processes the data set to format the date and time columns, and to identify missing data points reporting their position within the time series (variable ‘na.id’). The user fills the gaps using adequate strategies and creates a new input file (stored in variable ‘fill.points’) containing the values to fill in within the time series. A reference PAR estimate is obtained as a constant fraction of solar radiation using the conversion factor proposed by [Meek et al., 1984]. The script then calculates an average daily value of solar radiation and integrates the reference PAR over the daytime period to obtain a daily value. The script ends by generating a final table (‘ws.results’) reporting daily values of solar radiation (maximum and mean in W m-2), and maximum, mean, and minimum reference PAR values in units of (μmol m-2 d-1) and (mol m-2 d-1).
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