[GRASS-user] Pre-processing LANDSAT TM Orthorectified images from GLCF

[Markus Neteler]

On Mon, Jun 2, 2008 at 7:50 AM, maning sambale
<emmanuel.sambale at gmail.com> wrote:
> Hi,
>
> For a project I am involved with, we are conducting landcover
> classification from LANDSAT TM (orthorectified) data downloaded from GLCF.
> We are now in the process on pre-processing the image and then conduct
> classification using i.smap.
>
> Following the GRASS book, we will be conducting the pre-processing
> steps outlined:
>
> 1. calibration from DN to apparent radiance at sensor - gain/bias offsets
>
> following grass book 2nd ed. (page 222)
> r.mapcalc "band.rad = ((LMAX - (LMIN))/(255.0 - 1.0)) * (band -1.0) + (LMIN)"
>
> or
>
> i.landsat.toar

i.landsat.toar is the more sophisticated approach (or, easier since you
don't need to write the formula manuallly).

> 2. correction for atmospheric effects
>
> use i.atcorr
> problem: the metadata supplied by GLCF does not indicate image acquisition time
> sample metadata: http://tinyurl.com/6oo428
>
> or use
> i.landsat.dehaze

AFAIK LANDSAT is sun-synchronous, it passes in the local morning time
(something like 10:30-11:00).

Maybe this helps:
http://earthobservatory.nasa.gov/MissionControl/overpass.html

i.atcorr is the sophisticated correction, i.landsat.dehaze only a simple
approach based on image statistics.

> 3. correction for topographic/terrain effects (most of my study area
> are in maountainous regions)
> use book 2nd ed. (page 226) "cosine correction"
> using r.sunmask, r.mapcalc
> Problem: again, no image acquisition time

(see above). "cosine correction" is a simple approach. See also
i.topo.corr (from GRASS AddOns).

> 4. removal of clouds
> use i.landsat.acca
> https://svn.osgeo.org/grass/grass-addons/imagery/i.landsat.acca/

Never tried, please report back.

> The beauty with GRASS and the GRASS book is that it has the
> tools/modules I need for this project, however, I find it difficult to
> choose which one I should use (i.atcoor or i.landsat.dahaze?).  Am I
> following the steps in correct order?  Or is it necessary to do all
> this?  Reading from GLCF documentation, they did orthrectification for
> this image already.
>
> Any pointers would be very helpful.

I have collected all this now in
http://grass.osgeo.org/wiki/Image_processing#Preprocessing

Feel free to further improve that Wiki page.

Markus