[GRASS-user] Strange r.slope.aspect output of Aster dem : slope calculations

GRASS GRASS user
1

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over the full French territory, and as a result got large artefact stripes on a south west-north east axe? When could it come from (inadequate re-projection, the slope routine or the aster data)?

The stripped result :
https://www.dropbox.com/s/fcxaei1be9wsmka/slopeFranceSmall.png
https://www.dropbox.com/s/b52k5co46ujmpt7/slopeFrance.jpg

Thank you in advance, Manuel

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2

On Fri, Dec 20, 2013 at 4:54 PM, manuel.martin
<manuel.martin@orleans.inra.fr> wrote:

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over the
full French territory, and as a result got large artefact stripes on a south
west-north east axe? When could it come from (inadequate re-projection, the
slope routine or the aster data)?

Do you use these data in their original projection?

BTW:
you may use the new EU-DEM: Digital Surface Model at 25m

I made some screenshots at:
http://courses.neteler.org/eu-dem-new-digital-surface-model-at-25m/

and continue to use it for various applications:
http://courses.neteler.org/using-the-25m-eu-dem-for-shading-openstreetmap-layers/

(r.sun based analysis coming soon)

Markus

3

On Fri, Dec 20, 2013 at 12:37 PM, Markus Neteler <neteler@osgeo.org> wrote:

On Fri, Dec 20, 2013 at 4:54 PM, manuel.martin
<manuel.martin@orleans.inra.fr> wrote:
> Hi all,
> I just computed the slope using r.slope.aspect on the Aster data over the
> full French territory, and as a result got large artefact stripes on a
south
> west-north east axe? When could it come from (inadequate re-projection,
the
> slope routine or the aster data)?

Do you use these data in their original projection?

Hi, I would say that problem is in the DEM. Maybe the DEM needs some

cleanup (such as smoothing by r.neighbors). Using lower resolution (less
detailed) may help (r.resample probably needed). Blue stripes are probably
places where the elevation changes a lot and thus creating slopes.

So, using EU-DEM might be a good solution.

Vaclav

BTW:

you may use the new EU-DEM: Digital Surface Model at 25m

I made some screenshots at:
http://courses.neteler.org/eu-dem-new-digital-surface-model-at-25m/

and continue to use it for various applications:

http://courses.neteler.org/using-the-25m-eu-dem-for-shading-openstreetmap-layers/

(r.sun based analysis coming soon)

Markus
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4

On 20/12/13 16:54, manuel.martin wrote:

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over
the full French territory, and as a result got large artefact stripes on
a south west-north east axe? When could it come from (inadequate
re-projection, the slope routine or the aster data)?

The stripped result :
https://www.dropbox.com/s/fcxaei1be9wsmka/slopeFranceSmall.png
https://www.dropbox.com/s/b52k5co46ujmpt7/slopeFrance.jpg

Could these stripes be related to the ASTER satellite's path ?

See the map of Terra paths here: http://www.science.aster.ersdac.jspacesystems.or.jp/en/about_aster/calendar/index.html

Moritz

5

... sorry, if this has alredy been considered:
http://gis-lab.info/docs/aster-report-v3.pdf

Am 23.12.2013 10:44, schrieb Moritz Lennert:

On 20/12/13 16:54, manuel.martin wrote:

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over
the full French territory, and as a result got large artefact stripes on
a south west-north east axe? When could it come from (inadequate
re-projection, the slope routine or the aster data)?

The stripped result :
https://www.dropbox.com/s/fcxaei1be9wsmka/slopeFranceSmall.png
https://www.dropbox.com/s/b52k5co46ujmpt7/slopeFrance.jpg

Could these stripes be related to the ASTER satellite's path ?

See the map of Terra paths here: http://www.science.aster.ersdac.jspacesystems.or.jp/en/about_aster/calendar/index.html

Moritz
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6

On Fri, Dec 20, 2013 at 4:54 PM, manuel.martin
<manuel.martin@orleans.inra.fr> wrote:

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over the
full French territory, and as a result got large artefact stripes on a south
west-north east axe? When could it come from (inadequate re-projection, the
slope routine or the aster data)?

The stripped result :
https://www.dropbox.com/s/fcxaei1be9wsmka/slopeFranceSmall.png
https://www.dropbox.com/s/b52k5co46ujmpt7/slopeFrance.jpg

ASTER data are not really suitable to derive a DEM, your example is
another demonstration that an ASTER-derived DEM contains artefacts.
SRTM DEMs are without these artefacts.

Markus M

7

Thanks for the replies, we actually derived SRTM DEMs and yes this thime without artifacts.

Cheers

On 01/08/2014 09:16 PM, Markus Metz wrote:

On Fri, Dec 20, 2013 at 4:54 PM, manuel.martin
<manuel.martin@orleans.inra.fr> wrote:

Hi all,
I just computed the slope using r.slope.aspect on the Aster data over the
full French territory, and as a result got large artefact stripes on a south
west-north east axe? When could it come from (inadequate re-projection, the
slope routine or the aster data)?

The stripped result :
https://www.dropbox.com/s/fcxaei1be9wsmka/slopeFranceSmall.png
https://www.dropbox.com/s/b52k5co46ujmpt7/slopeFrance.jpg

ASTER data are not really suitable to derive a DEM, your example is
another demonstration that an ASTER-derived DEM contains artefacts.
SRTM DEMs are without these artefacts.

Markus M

--

----------------0----0------
INRA - InfoSol
Centre de recherche d'Orléans
2163 Avenue de la Pomme de Pin
CS 40001 ARDON
45075 ORLEANS Cedex 2
tel : (33) (0)2 38 41 48 21
fax : (33) (0)2 38 41 78 69
http://www.gissol.fr
----0----0------------------