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

maning sambale emmanuel.sambale at gmail.com
Mon Jun 2 01:50:21 EDT 2008


For a project I am involved with, we are conducting landcover
classification from LANDSAT TM (orthorectified) data downloaded from
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)"



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

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

4. removal of clouds
use i.landsat.acca

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.



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