Ra {MeTo}

Extraterrestrial radiation

Description

Extraterrestrial radiation [MJ/(m2 time)] in dependence to time, latitude and longitude.

Usage

Ra(x, lat.rad = NULL, lat.deg = NULL, long.deg, tl, control = list(Lz = 345))

Arguments

x

date-time object or day of the year (must be date-time object if calculation period is smaller 1 day)

lat.rad

latitude [rad]. Use either lat.rad or lat.deg. Latitude is positive for the northern hemisphere and negative for the southern hemisphere

lat.deg

latitude [degree]. Use either lat.deg or lat.rad. Latitude is positive for the northern hemisphere and negative for the southern hemisphere

long.deg

longitude of the measurement site (degrees east of Greenwich) (only needed for periods shorter 1 day)

tl

length of calculation period [hour] (1 for hourly period, 0.5 for a 30-minute period or 24 for daily period). Only needed if 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

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

control:

Lz (for periods < 1 day):
longitude of the centre of the local time zone (degrees west of Greenwich)
- 0 for Greenwich
- 345 for Germany
- 330 for Cairo (Egypt)
- 255 for Bangkok (Thailand)
- 75, 90, 105 and 120 for Eastern, Central, Rocky Mountain and Pacific time zones (United States)

Note

eq. 21 (period = 1 day) and eq. 28 (hourly or shorter) of the 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

# --------------------------------------------
#  Daily period
# --------------------------------------------

Ra(x = 105, lat.deg = 13.73)

# --------------------------------------------
#  Hourly period
# --------------------------------------------

Ra(x = as.POSIXct(c('2018-10-01 14:30', '2018-10-01 15:30')),
   lat.deg = 16.21, long.deg = 343.75, control = list(Lz = 15))

Ra(x = as.POSIXct('2018-10-01 14:30'), tl = 1,
   lat.deg = 16.21, long.deg = 343.75, control = list(Lz = 15))