[GRASS-user] r.sun - beam irradiance issues in mountain area with a high relief energy

[Anna Petrášová]

This could be potentially a problem described in
https://github.com/OSGeo/grass/pull/2534.
Could you try to run this with the changes in the PR?

Anna

On Tue, Jan 31, 2023 at 4:05 PM Helmut Kudrnovsky <hellik at web.de> wrote:

> hi,
>
> given a a mountain area with a high relief energy based upon an ALS DEM
> with a 1x1m resolution
>
> and system: winGRASS GIS 8.2.1
>
> g.region -p
> projection: 99 (MGI / Austria Lambert)
> zone:       0
> datum:      hermannskogel
> ellipsoid:  bessel
> north:      358599.5
> south:      345055.5
> west:       221323.5
> east:       236275.5
> nsres:      1
> ewres:      1
> rows:       13544
> cols:       14952
> cells:      202509888
>
> DEM range of data: min = 1197.4  max = 3496.68
>
> the horizon rasters are calculated by
>
> r.horizon elevation=als at data step=30 maxdistance=5000 output=horangle
>
> r.sun is calculated for 15 June
>
> r.sun elevation=als at data aspect=als_aspect at data slope=als_slope at data
> horizon_basename=horangle horizon_step=30 beam_rad=beam_rad166 day=166
> nprocs=2 npartitions=2
>
> see the result screenshot in https://pasteboard.co/YShtdFG8C7jk.png
>
> o the high peak has northern, eastern and southern oriented steep slopes
> o the more red, the higher beam irradiance calculated by the r.sun command
> above
> o the southern oriented footslopes show a high beam irradiance (as
> exptected)
> o the southern oriented and very steep slopes around the peak show a
> similar low beam irradiance as the northern slopes (not expected)
>
> I have issues to interpret the results, especially the last pattern:
>
> o Could be the lower beam irradiance in the very southern oriented slopes
> nearby the peak due to the very steep slope?
> o Do slopes with a high inclination (though southern oriented) reduce beam
> irradiance in the implemented model?
>
> Kind regards
> Helmut
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