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Can you help me to calculate solar radiation from GTOPO30 DEM image at the 30 m spatial resolution. I'm trying to do this many times using spatial analysis-solar radiation calculation tool in arcgis. But there always appeared error message saying unknown problem. what does it mean? Is there anyone who has a experince with this. your suggestion will help me a lot.

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GTOPO30 is approximately 1km resolution, not 30 meter, and my guess is that the algorithm used makes low resolution data inappropriate for analyzing solar radiation. –  scw May 24 '11 at 7:35
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The solar radiation calculation is computationally expensive, and it isn't something that can be run on extremely large regions. I've run it on a 250 km^2 area which took three days at a low resolution, so it may not be feasible to do for all of Mongolia. See this thread and the help page for further background on the constraints. If you are set on performing the analysis, divide up your raster into small regions, and run it independently on each. With a little experimentation, you should be able to determine the size at which it runs reliably.

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Sorry I'm confused with the resolution of GTOP030. My area of interest is whole territory of Mongolia. it is a quite big area (1,566 sq km). Can I use SRTM elevation data at the resolution of 90 m. –  user3063 May 22 '11 at 21:10
    
Wouldn't this answer be better as a comment? –  Sean May 23 '11 at 19:15
    
@Sean Separated out the 'comment' component and rewrote my answer. –  scw May 24 '11 at 7:44
    
Thanks for your helps. Another one think I'd like to ask is: actually I need solar radiation data for the last 8-10 years for my temporal anaysis. Is it possible I can get these information from DEM. Is there DEM data 'during 10 years'? I downloaded GTOPO30, SRTM 30m, 90m. But these DEM data were acquired within just one year. –  user3063 May 26 '11 at 15:05
    
DEM data isn't something which changes much over time, particularly not on an annual basis. But certainly other factors which have major effects on solar radiation such as cloud cover and light dispersal do change over time, if you're trying to produce a systematic model you may want to also think about those. –  scw May 26 '11 at 19:05
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