[GRASS-user] Question about r.sun2 and r.horizon

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Wed Jun 18 18:49:14 EDT 2008

Just reporting how I finally calculated the global_rad map.

>r.slope.aspect  elev=srtm3_for_global_rad  slope=slope_for_global_rad
aspect=aspect_for_global_rad  format=degrees

>i.latitude input=srtm3_for_global_rad latitude=latitude_for_global_rad

>i.longitude input=srtm3_for_global_rad

>r.horizon elevin=srtm3_for_global_rad step=45 horizon=horizon45  ###
This gives radians as an output!

>for i in `seq 92 304`; do r.sun2 -s --o  elevin=srtm3_for_global_rad
aspin=aspect_for_global_rad  slopein=slope_for_global_rad  alb=0.23
lin=5.2  horizon=horizon45  horizonstep=45  glob_rad=global_rad_$i day=
$i; done   

### After Hamish' comments and a bit of testing I found no difference
when using different values on the "lat=" parameter. So it really stays
out of the game (?)

>r.mapcalc global_rad_sum=0 && for i in `seq 92 304`; do r.mapcalc
global_rad_sum=global_rad_sum + global_rad_$i; done 

>r.mapcalc global_daily_avg=global_rad_sum / 212

>r.mapcalc global_daily_avg_kJ="int(global_daily_avg * 3.6)" 

>r.mapcalc formula="global_daily_avg_kJ / 2450 * (0.025000 *
temperature_int + 0.080000)"   ### P(otential) E(vapo)T(ranspiration)

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