Hi Hamish, now I can't verify in which way the sun map made with arcGIS was done (albedo, atmospheric turbidity…) maybe the differences depend on terrain shadow effect that I have not considered in grass map.
If I want to add this effect to your script for global radiation, how can I do? And moreover, will your script calculate automatically slope and aspect from DTM or it use the default values? Thanks Salvatore Il giorno 06/set/2011, alle ore 05:13, Hamish ha scritto: > Salvatore wrote: >> thanks for the script, it works. I want to be sure that the >> result is the global radiation map expressed in W/m2/yr (or >> it is W/pixel/yr?). I compare it with ones made with ArcGis >> and the values are differents. > > how much different? just by a few percent or wildly different? > > > I have just done some back-of-the-envelope calculations based > on Spearfish's latitude on Sept 21st and the solar constant, > both instantaneous at 12 noon, and a rough integration over the > day, and both answers of my very crude calcs come within 3% and > 8% of the presumably much more correct r.sun results. (and I'd > expect the atm scattering to take more out in the dawn/dusk > hours so that increase to 8% diff for the daily sum doesn't > worry me) So they would seem to me to be in the correct order of > magnitude. > > > It is not surprising that ESRI is using a different method/ > algorithm than r.sun uses, and if so not surprising that the > answer would be slightly different. Can you hold the albedo and > atmospheric turbidity identical in both methods? > > the basic integration of flux from a point source following a > curve for a known geometry should be rather similar, but the > fancy atmospheric and ground albedo adjustments is where I'd > expect to see the differences and interesting science. > > >> Another question…the albedo effect is excluded? > > the albedo in r.sun is either given by a raster map containing > ground coefficients, or the "alb" parameter, which defaults > to 0.2. > > > Hamish > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
