[GRASS-user] Estimating Albedo from Landsat

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Mon Sep 13 08:40:51 EDT 2010

Daniel Victoria wrote:

> I did not use i.landsat.toar. I converted the DN values to radiance
> manually, using r.mapcalc and the formula and  coefficients provided.

> Are you going to use i.atcorr?

Currently I only require to automatically detect clouds and nothing more than 
that. Since I don't require (at the moment) surface (or top-of-canopy) 
reflectances, I guess I don't need to run "i.atcorr".

I will use i.landsat.toar (with the default option "method=uncorrected") and 
i.landsat.acca afterwards.

> I'm still trying to figure out which is the correct procedure for i.atcorr:
> 1) Convert DN to radiance and run i.atcorr (wiki example)
> 2)  Use DN values in i.atcorr (man page exemple)


the "i.atcorr" module (which implements the 6S algorithm) expects either (toa) 
radiance or (toa) reflectance. Option "2" above is not correct.

> And also, what are the output units since they appear to be scaled from 1
> to 255

I am puzzled as well :-( -- I guess it's a (re-)scaling related puzzle? Will 
post again when I'll get the answer to this.

FWIW, I am convinced by writers (e.g. Lillesand and Kiefer) supporting that 
the term "correction" is not exactly correct in the case of retouching 
remotely sensed data with the aim to "remove" atmospheric effects.

Best regards, Nikos


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