Hi all,<br>
Right now i'll go ahead with clear sky algorithms, and i'll order
observed data and try to come up with a real-sky correction based on
cloud cover, r.sun output and observed data..<br>
But i noticed a major problem as i ran r.sun with the shadowing effect (-s) flag:<br>
Much of the centre of India ends up with 0 beam radiation!!<br>
See attached images- which are beam radiation output for the same day,
with and without shadow. yellow color is zero beam radiation.<br>
<br>
THE REASON FOR THIS (I think)<br>
I used the GTOPO30 (approx. 1km ORIGINAL res) elevation and derived
slope and aspect as input to r.sun. HOWEVER, i never used the original
GTOPO30 resolution- I just brought it into my current region, which is
based on my base datasets of meterology from CRU at 0.5deg resoluton
(approx. 50km? resolution), using r.in.bin directly into my
coarse region (0.5 deg).<br>
I think as a result, the shadowing effect in r.sun, which takes the max
altitude from 4 nearest cells, is reaching across 50km(!) Hence with
the Himalayas in the north and Western Ghats mountains in the west,
most of central India gets 0 beam radiation!<br>
At this point, I would like some help in how i go about this. <br>
1. How Can i import the GTOPO30 into my current mapset while at the same time creating a new region (say gtoporegion)?<br>
<br>
2. Then i think i should calculate my slopes and aspects at the orginal GTOP30s resolution (30arcseconds) in gtoporegion<br>
<br>
3. Then I should calculate all the r.sun maps in this gtoporegion<br>
<br>
4. Finally I guess I can take these fine resolution solar maps
into my 0.5degree resolution region using r.resample.rst, and
continue ..??<br>
<br>
Any suggestions appreciated! I'm not very familiar with having
different resolutions/regions in the same mapset (have read the
documentation).<br>
<br>
thanks,<br>
vishal <br><br><div><span class="gmail_quote">On 8/23/06, <b class="gmail_sendername">Hamish</b> <<a href="mailto:hamish_nospam@yahoo.com">hamish_nospam@yahoo.com</a>> wrote:</span><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Massimiliano Cannata wrote:<br>> Actually I don't really know what is the influence of cloud cover on<br>> radiation (linear function between cloud cover and energy<br>> filtered????),<br><br>on a cloudy day the direct sunlight is reduced, and the diffuse in
<br>increased. e.g. in the fjords I study there are many places which<br>never get direct sunlight. We have deployed subsurface PAR light-loggers<br>in paired sunny/shaded sites and the shaded side actually gets more<br>light on cloudy days.
<br><br><br>Hamish<br><br>_______________________________________________<br>grassuser mailing list<br><a href="mailto:grassuser@grass.itc.it">grassuser@grass.itc.it</a><br><a href="http://grass.itc.it/mailman/listinfo/grassuser">
http://grass.itc.it/mailman/listinfo/grassuser</a><br></blockquote></div><br>