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Dear All, Is there anyone with experience in the Area Solar radiation tool of the Spatial Analyst? I was getting some seriously unreliable results so I run a simple analysis using a flat DEM and then compared these with average values based on measurements. I have included a word file explaining the problem, along with the flat DEM (please use the latitude shown on the word file if you re-run the analysis to check results I provide). I am running the analysis for two days, one typical for winter (16/2) and one for summer (11/6). I also use complete transmission and totally clear sky conditions to compute a value that can be compared to the Extraterrestrial/exo-atmospheric irradiance on horizontal. The results for the Global, Beam and Diffuse irradiances are entirely inaccurate (as an indication, the annual results underestimated the Global horizontal irradiance by 75%) and I would appreciate any help on this. Keep in mind that I am new in GIS, so please excuse me if I have done something really stupid:). I am also confused with the name of the tool, what is the difference between the Area Solar Radiation Tool and the Solar Analyst or TopoView that I usually come across in the literature? Thank you in advance, Kind Regards Eleni
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06-16-2011
06:11 AM
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Further to my previous post, in the Webhelp topic of ArcGIS 9.2 (not 9.3) I read: "transmissivity... is the ratio of solar radiation outside the atmosphere to that reaching the earth's surface (averaged all wavelengths) for the shortest path (in the direction of the zenith)". If what is meant by the author is actually the reverse ratio (global to extraterrestrial), that would equal to the clearness index. However my understanding is that the software requires as input the proportion of extraterrestrial that finds its way as beam irradiance at sea level. Could someone clarify this?
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05-23-2011
01:29 AM
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Dear all, I would appreciate your help on the description of the atmospheric transmissivity parameter used in Topo view/Solar Analyst. In the Help section in ArcGIS 9.3 it is defined as the ratio of global irradiance on earth to extraterrestrial solar radiation in the direction of the zenith. Nevertheless in journal articles referring to the use of Solar Analyst, I have seen it defined as the transmissivity of beam irradiance only (this was my understanding too as it is used only for the calculation of the direct irradiance only), through cloud particles, aerosol particles (natural and artificial) and molecules of gases [calculated as ??=kt (1-kd), where kt is the clearness index and kd the diffuse ratio)). Which of the two is the correct one for the algorithm employed by the Solar Analyst? Thank you in advance for any replies.
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05-20-2011
07:51 AM
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