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

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@data step=30 maxdistance=5000 output=horangle

r.sun is calculated for 15 June

r.sun elevation=als@data aspect=als_aspect@data slope=als_slope@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

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@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@data step=30 maxdistance=5000 output=horangle

r.sun is calculated for 15 June

r.sun elevation=als@data aspect=als_aspect@data slope=als_slope@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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Hi Anna,

This could be potentially a problem described in https://github.com/OSGeo/grass/pull/2534.

yes, it seems to be similar.

Could you try to run this with the changes in the PR?

no chance to test the PR at the moment.

Best
Helmut

Hi Anna,

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?

I hopefully correctly applied this PR now here locally in my winGRASS. :wink:

DEM: Airborne Laser Scan 1 x 1 m

projection: 99 (MGI / Austria GK West)
zone: 0
datum: hermannskogel
ellipsoid: bessel
north: 218281.5
south: 204874.5
west: 49389.5
east: 62610.5
nsres: 1
ewres: 1
rows: 13407
cols: 13221
cells: 177253947

*patched r.sun*
r.sun elevation=laser_dgm@data aspect=laser_dgm_aspect@data slope=laser_dgm_slope@data horizon_basename=horangle horizon_step=30 beam_rad=beam_rad_166 day=166
Number of threads <1>
Mode 2: integrated daily irradiation for a given day of the year
Using Linke constant: 3.000000
Using albedo constant: 0.200000
Using slope map <laser_dgm_slope@data>
Using aspect map <laser_dgm_aspect@data>

*elevation - computional region

https://pasteboard.co/g82fQtvdcbeE.png

*aspect - computional region

https://pasteboard.co/jV36f8fb1xoY.png

*beam irr 166 - computional region

https://pasteboard.co/no7YUTqNtEPg.jpg

*aspect zoom to the high altitudinal south oriented mountain face with a high slope gradient and high local geomorphological variability

https://pasteboard.co/u10fbgnUU4nX.png

*slope zoomed to the high altitudinal south oriented mountain face with a high slope gradient and high local geomorphological variability

https://pasteboard.co/5FeilT6qRj7t.png

*slope zoomed only 50-90 degrees on the high altitudinal south oriented mountain face with a high slope gradient and high local geomorphological variability

https://pasteboard.co/ssmNEUWyagYe.png

*beam irr 166 zoom on the high altitudinal south oriented mountain face with a high slope gradient and high local geomorphological variability

https://pasteboard.co/PVSjFWy2qcOK.png

later on I'll post a screenshot of the not patched r.sun in 8.2.1

best
helli