[GRASS-user] Re: i.atcorr negative DEM

Elena Mezzini elena.mezzini at gmail.com
Tue May 17 16:08:35 EDT 2011


On Tue, May 17, 2011 at 9:22 PM, Elena Mezzini
<elena.mezzini at gmail.com> wrote:
> Hi all,
> I'm once again in trouble with i.atcorr in GRASS6.5.svn.
> I notice that my output reflectance images are strange: there are some
> areas
> that are really bright and other that are really dark. Both seem to match
> with my DEM raster.
> Could there be problems with negative values in DEM?? I'm in a coastal
> area
> and there are some real altitude negative values.

i.atcorr (the 6S code it is using to be exact) should treat negative
elevation values as elevation = 0. It is debatable if this is correct,
but in theory i.atcorr should behave accordingly. Actually, I am not
sure about it's behaviour for negative elevation values...

You could set all negative elevation values to zero, 


Ok, how can I do it?



run i.atcorr again and compare the results to the i.atcorr results using the
original DEM. If there are any differences that do not make sense,
please fill in a bug ticket.

Markus M


Thank you!

Elena


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