[GRASS-user] Correction of terrain effects for MODIS data?

Sat Dec 1 16:11:28 EST 2007

Markus,

thank you for the interest.

On Sat, 2007-12-01 at 12:54 -0800, Markus Neteler wrote:
> Hi Nikos,
> 
> do you use
> MODIS/Terra Surface Reflectance Daily L2G Global 250m SIN Grid V005
>  http://edcdaac.usgs.gov/modis/mod09gqv5.asp
> MODIS/Aqua Surface Reflectance Daily L2G Global 250m SIN Grid V005
>  http://edcdaac.usgs.gov/modis/myd09gqv5.asp
> ?
Yes. And a earlier image (version 4) in 2006.
> 
> Did you check the ATBD08 (Algorithm Technical Background Document)?
> http://modis.gsfc.nasa.gov/data/atbd/atbd_mod08.pdf
> But indeed - it doesn't seem to mention it.
I ve read almost every line from the MODIS algorithm.

There seems to be an attempt to couple BRDF but no DEM is incorporated
in the approach.

I even contacted Kamel Didan working very close with MODIS-people and
knows the authors of ATBD. He pointed out to look for another paper and,
why not, contact the authors of ATBD. I am planning to do so.

FYI, I attach his reply below as a P.S.

> here maybe some pointers:
> http://scholar.google.com/scholar?q=modis+terrain+correction&hl=en&lr=&scoring=r&as_ylo=2002

I am looking at it now...
> 
> Markus

Best regards,

Nikos
---

P.S.

                              From: 
kamel <kamel at Ag.arizona.edu>
                                To: 
Nikos Alexandris
<nikos.alexandris at grid.unep.ch>
                                Cc: 
kamel at cals.arizona.edu
                           Subject: 
Re: Correction for terrain effects
in MODIS surface
reflectance products (?)
                              Date: 
Fri, 30 Nov 2007 09:30:25 -0700
(17:30 CET)

No problem, but I'm not an expert on atmosphere correction to give you
the most accurate & up to date answer.

Nonetheless, here is some info.

The current MOD09 surf. corr. algorithm does account for terrain relief,
but at a coarser resolution.
you can read their ATBD (it is very long)
http://modis-sr.ltdri.org/MAIN_SURFACE_PRODUCTAND%20USER%
20GUIDE/atbd_mod08.pdf

For a more accurate description of correction over rugged terrain look
at the Dozier paper:
J. Dozier and J. Frew, 1981: Atmospheric corrections to satellite
radiometric data over
rugged terrain. Remote Sens. Environ.,11,191-205.

Obviously it is important to account for the terrain relief (atmosphere
thickness) and aspect.
But it is quite hard in practice especially since you're limited with
your input data to the atmosphere 
correction model.  At coarse resolution it is even more complex because
of the complexity of the pixels.

For further information please contact Drs Alex and Eric they may have a
better idea and better suggestions.

Alex Lyapustin  alyapust at pop900.gsfc.nasa.gov

Eric Vermote   eric at ltdri.org 

Good luck,

K.Didan
AZ

> Dear Kamel,
> 
> I have a question... (again ;-| )!
> 
> How important do you think is a correction for terrain effects in a
> MODIS surface reflectance acquisition?
> 
> AFAIK,
> 
> only the MODIS algorithm does only atmospheric correction(s).
> 
> I did some test with a MODIS image (using GRASS-GIS) but the result
> doesn't look like what I want to have. It looks to bright!
> 
> Thank you in advance,
> 
> Nikos.

> 
> 
> Nikos Alexandris wrote:
> > 
> > Hi!
> > 
> > Will this approach enable a correction for terrain as well? I don't see
> > how I can incorporate elevation data or anything relevant.
> > 
> > I used the cosine correction approach which is described in GRASS-GIS in
> > order to correct a MODIS image. But the result is over-corrected (!) as
> > mentioned also in the book.
> > 
> > I am looking for a practical approach in order to minimize terrain
> > effects in a MODIS NIR surface reflectance acquisition. The area in
> > which I am interested to visually identify the land cover, is
> > mountainous. So any correction would be of great importance.
> > 
> > Thank you in advance.
> > 
> > On Fri, 2007-11-30 at 15:10 -0800, Hamish wrote:
> >> Nikos Alexandris wrote:
> >> > I tried to follow the example for correction of terrain effects in a
> >> MODIS
> >> > surface reflectance NIR band 
> >> > (...as far as I know, MODIS surface reflectance imagery is only
> >> corrected
> >> > for atmospheric effects).
> >> > 
> >> > I don't get the desired results... The output is too bright from what
> >> one
> >> > would expect it to be.
> >> > 
> >> > Any recommendations?
> >> 
> >> I've never used it for MODIS, but you could try i.landsat.rgb to see if
> >> that
> >> helps. (it wants three 0-255 bands, it doesn't care about it being
> >> LANDSAT or
> >> not)
> >> 
> >> 
> >> Hamish
> >> 
> >> 
> >> 
> >>      
> >> ____________________________________________________________________________________
> >> Never miss a thing.  Make Yahoo your home page. 
> >> http://www.yahoo.com/r/hs
> > -- 
> > Nikos Alexandris
> > .
> > Department of Remote Sensing & Landscape Information Systems
> > Faculty of Forestry & Environmental Sciences, Albert-Ludwigs-University
> > Freiburg
> > .
> > Tel.  +49 (0) 761 203 3697 / Fax.  +49 (0) 761 203 3701 / Skype:
> > Nikos.Alexandris
> > .
> > Address: Tennenbacher str. 4, D-79106 Freiburg i. Br., Germany
> > 
> >  
> > _______________________________________________
> > grass-user mailing list
> > grass-user at lists.osgeo.org
> > http://lists.osgeo.org/mailman/listinfo/grass-user
> > 
> > 
> 
-- 
Nikos Alexandris
.
Department of Remote Sensing & Landscape Information Systems
Faculty of Forestry & Environmental Sciences, Albert-Ludwigs-University Freiburg
.
Tel.  +49 (0) 761 203 3697 / Fax.  +49 (0) 761 203 3701 / Skype: Nikos.Alexandris
.
Address: Tennenbacher str. 4, D-79106 Freiburg i. Br., Germany
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