Hi all,<br>
<br>
the idea of converting elevation to degrees did'nt work out.<br>
<br>
i managed to project my latlong dem (30min, approx 960m
resolution) to lambert conformal conic, so elevations, and
coordinates are both in meters.<br>
<br>
then i ran r.sun with a fixed albedo of 0.23<br>
<br>
r.sun elevin=gtopo30 aspin=gtopoasp slopein=gtoposlope alb=0.23 beam_rad=beam1 diff_rad=diffuse1 refl_rad=reflect1 day=15<br>
<br>
i got some output that looks right for beam and diffuse radiation:
however, the reflected radiation map is almost all zero. there are some
small positive values near mountainous regions (~50 Whr/(m2-day)).<br>
<br>
since the albedo was 0.23, and the average global radiation i get is
about 5000 Whr/(m2-day), i cant understand why the reflected radiation
(Ri)is all zero. The manual says something about a factor related to
'fraction of ground viewed by an inclined surface' r<font size="1">g<font size="2">(g<font size="1">N).<br>
<br>
i.e. <font size="2">Ri = albedo* global radiation * </font></font></font></font>r<font size="1">g<font size="2">(g<font size="1">N)</font></font></font><font size="1"><font size="2"><font size="1"><font size="2"> <br>
<br>
so I assume then that this </font></font></font></font><font size="2">r</font><font size="2">g(gN) factor </font><font size="1"><font size="2"><font size="1"><font size="2"> must be causing the problem..<br>
<br>
does anyone have any idea why this may be happening and what to do about it?<br>
<br>
also, i wanted to report that what i'm getting for beam, diffuse and
reflected output now with lambert projections and the original 30min
(960m) resolution float dem,<br>
is almost the SAME as in the beginning of this saga, when i was using
latlong at coarse 0.5 degree resolution and integer dem! The difference
may only be in the output when using the -s flag for accounting for
shading.<br>
However, the -s flag option took some half hour to run at the 960m resolution..<br>
<br>
There are many other things that happened in between that were funky, but i guess i should save you all from that stuff:)<br>
<br>
cheers,<br>
vishal<br>
</font></font></font></font><br>
<br>
<br><div><span class="gmail_quote">On 8/28/06, <b class="gmail_sendername">Glynn Clements</b> <<a href="mailto:glynn@gclements.plus.com">glynn@gclements.plus.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;">
<br>Vishal Mehta wrote:<br><br>> so should i change the Proj_units file to:<br>><br>> unit: degree<br>> units: degrees<br>> meters: 111300 * cos(y())<br><br>It won't matter in this case; both r.slope.aspect
and r.sun handle<br>lat/lon locations separately.<br><br>--<br>Glynn Clements <<a href="mailto:glynn@gclements.plus.com">glynn@gclements.plus.com</a>><br></blockquote></div><br>