estRs | R Documentation |
Rs is calculated from relative sunshine duration and extraterrestrial radiation with the Angstrom formula.
estRs( x, n, lat.rad = NULL, lat.deg = NULL, tl, control = list(as = 0.25, bs = 0.5) )
x |
date-time object or Day of the year |
n |
actual duration of sunshine [hour] |
lat.rad |
latitude [rad] (either lat.rad or lat.deg). Latitude is positive for the northern hemisphere and negative for the southern hemisphere |
lat.deg |
latitude [degree] (either lat.rad or lat.deg). Latitude is positive for the northern hemisphere and negative for the southern hemisphere |
tl |
length of calculation period [hour] (1 for hourly, 0.5 for a 30-minute or 24 for daily period). Only needed if length of x is date-time object with length of 1. |
control |
list for control parameters and empirical factors defined in |
as: regression constant, expressing fraction of extraterrestrial radiation reaching earth on overcast days (n = 0) (default = 0.25)
bs: as + bs fraction of extraterrestrial radiation reaching earth on clear days (n = N) (default = 0.5)
must be provided as.numeric (1-366) or as a common date-time object (e.g, POSIXct, POSIXlt or Date objects). All formats for which is.timepoint from the lubridate package returns TRUE can be used
solar or shortwave radiation (Rs) [MJ/(m2 day)]
eq. 35 of reference
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. (1998). Crop evapotranspiration-Guidelines for computing crop water requirements-FAO Irrigation and drainage paper 56. FAO, Rome, 300(9).
estRs(x = 135, n = 7, lat.rad = NULL, lat.deg = -22.9)
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