Computes extra-terrestrial solar radiation

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Description

solarRad computes the solar radiation received at the top of the Earth's atmosphere on a horizontal surface. This radiation will change during the day and will be different at different latitudes and in different seasons.

Usage

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solarRad(img, day)
solarRad12M(img, outFl, ...)

Arguments

img

object of class SpatialGridDataFrame that provided a projection class and a bbox attributes. The nature of the data.frame that contains the attribute data is not relevant. It must be in geographic coordinates.

day

The number of the day (from 1 to 365) to compute extra-terrestrial radiation.

outFl

A list of 12 file names to save the results.

...

Any unmatched parameter will be passed to the writeGDAL routine.

Details

The output is expressed in cal/cm2*day.

This function runs unnoticed within petHgsm, but can be executed manually.

Value

solarRad returns a single image corresponding to the specified day, as a SpatialGridDataFrame class. solarRad12M writes 12 images to disk in the format especified by the GDAL drivername parameter.

Author(s)

Gabriel del Barrio, Marieta SanJuan & Alberto Ruiz

References

Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56

See Also

petHgsm

Examples

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#not run
#aux=readGDAL('iberia_mask')
#calc the extraterrestial radiation the 15-agost
#Rad=solarRad(aux,227)
#writeGDAL(Rad,'solarrad_15ago')
#or to calculate and write to disk, the radiation of the twelve months
#RadFileNames=paste('rad',month.abb,sep='')
#solarRad12M(img,RadFileNames)