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

[Helmut Kudrnovsky]

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