[GRASS-dev] Changes to r.sun made Feb 2006 [resolved]

[Dylan Beaudette]

Sorry for the noise, it looks like this was an operator error on my part.

Cheers,

Dylan

PS: with even better results from r.sun:

http://169.237.35.250/~dylan/temp/11-yr_variation_vs_modeled.png

when using longer term averages, the R^2 goes to 0.95 ! (right hand
sub-figure), but still working on optimal Linke turbidity values.




On 11/28/06, Dylan Beaudette <dylan.beaudette at gmail.com> wrote:
> Hi everyone,
>
> I am repeating an experiment, originally conducted Feb 7th 2006, comparing the
> output from r.sun with real data from a weather station.
>
> On Feb 7th, 2006 the output from r.sun (computed with customized linke
> turbidity values) very closely matched the weather station data.
>
> As of today the exact same experiment gives slightly different results:
> 1. the correlation between r.sun and the weather station is nearly identical
> 2. the output from r.sun (specifically the beam component) is about 1500
> Wh/sq. meter/day higher than it should be.
>
> The only thing that has changed since I last conducted this experiment was
> r.sun. From the CVS server it looks like r.sun/main.c was altered shortly
> after I did my original experiment:
>
> -----------------------------------------------------------------------------------------------
> Revision 2.14 / (as text) / (view) - annotate - [select for diffs] , Tue Feb
> 21 10:00:52 2006 UTC (9 months ago) by markus
> Branch: MAIN
> Changes since 2.13: +28 -174 lines
> Diff to previous 2.13
>
> Jaro Hofierka: new shadow algorithm; dist param changed to fixed value;
> correction factor for shadowing to account for the earth curvature
> -----------------------------------------------------------------------------------------------
> http://freegis.org/cgi-bin/viewcvs.cgi/grass6/raster/r.sun/main.c
>
>
> In summary, the diffuse component of the modeled solar radiation is nearly the
> same as it was when computed by r.sun Feb 7 2006. The beam component is now
> about 1500 Wh/sq m / day higher than it was as on Feb 7 2006.
>
> This brings up an interesting question: which results from r.sun where the
> most representative of reality ? I noticed that the changes made to r.sun
> involved a shadow algorithm- yet my weather station (and modeled area) are
> not greatly affected by the shadowing of adjacent terrain.
>
> Any thoughts on how to best proceed would be greatly appreciated.
>
> PS:
>  the original results were mentioned in a previous message to the GRASS list
> on Feb 8 2006.
> http://www.nabble.com/-GRASSLIST%3A10214--some-nice-results-from-r.sun-t1087635.html
>
> --
> Dylan Beaudette
> Soils and Biogeochemistry Graduate Group
> University of California at Davis
> 530.754.7341
>
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