On Mon, Jun 2, 2008 at 7:50 AM, maning sambale <[EMAIL PROTECTED]> 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 _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-user