estRs {MeTo}

Estimate solar radiation (Rs)

Description

Rs is calculated from relative sunshine duration and extraterrestrial radiation with the Angstrom formula.

Usage

estRs(
  x,
  n,
  lat.rad = NULL,
  lat.deg = NULL,
  tl,
  control = list(as = 0.25, bs = 0.5)
)

Arguments

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 controlDefaults and constDefaults (see Details)

Details

control:

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)

x:

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

Value

solar or shortwave radiation (Rs) [MJ/(m2 day)]

Note

eq. 35 of reference

References

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).

Examples

estRs(x = 135, n = 7, lat.rad = NULL, lat.deg = -22.9)