swrad: Predict shortwave radiation on a surface
In rforge/microclim: Microclimate predictions

Description Usage Arguments Details Value Author(s) See Also Examples

View source: R/swrad.R

Standard prediction for shortwave radiation on a surface of given slope and aspect at a given time, given an observed value for shortwave radiation on a horizontal surface.

1	swrad(sw, slope, aspect, lat, day, elevation = 0, soltime, localtime, lon, merid = 0, dst = 0, trans0 = 0.2, ...)

`sw`	Shortwave radiation (in Watts per square metre) incident on horizontal ground. May be obtained from regional weather station or reanalysis data.
`slope`	Slope, in degrees from horizontal
`aspect`	Aspect, in degrees clockwise from north
`lat`	Latitude, in degrees
`lon`	Longitude, in degrees east from Greenwich
`soltime`	Local solar time, in hours from midnight
`localtime`	Local clock time, in hours from midnight (used if `soltime` is missing)
`day`	Day of the year (1 - 365)
`elevation`	Elevation of the site, in m
`merid`	Longitude of local standard time meridian, in degrees east from Greenwich. Thus the default (0) corresponds to the Greenwich mean time meridian; for Central European time (most of Western Europe except UK, Eire and Portugal), use merid = 15.
`dst`	Correction for summer time (=1 if local time has been adjusted for summer daylight-saving time, =0 if not)
`trans0`	typical transmission (proportion) of short-wave radiation through overcast sky. If in doubt, leave at 0.2.
`...`	Additional arguments to pass to subsidiary functions

The time when sw is observed should be specified by either localtime or soltime; the output will pertain to the same time. The function does two things: (1) it standardises the shortwave radiation with respect to the expected shortwave radiation at the specified time, and it applies solarindex to obtain a prediction for the specified slope and aspect. The calculations involve converting the horizontally-incident radiation to direct beam radiation with reference to the Sun's height; if this is less than 20 degrees, a warning is given to indicate that results may be unreliable. In that case, it may be better to use function srad.raster with an estimate for transmission based on cloud cover or other data.

Predicted short-wave radiation, in Watts per square metre. If any of the arguments comprise more than a single value (possibly rasters), they should be equal to each other in dimensions and extent and the output will be of corresponding size. For predictions over a landscape raster, see swrad.raster.

Jon Bennie

swrad.raster