[GRASS-user] i.atcorr - Landsat 8 Atmospheric correction

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I am trying to apply atmospheric correction to Landsat 8 scenes using i.atcorr. I have read lots of discussion about it, but I cannot seem to figure out the right way to use it. After tons of tests I am still struggling with the correct input and output range.

The results deriving from radiance as input and from reflectance as input are different! The correct flags are used and the radiance and reflectance values are from i.landsat.toar and their validity is checked through the mapcalculator by computing them manually from the .mtl file data.

So, I have radiance and reflectance and try to get the i.atcorr results. I try several combination of input and output range and the only ones that seem to produce a nice RGB are:

Input: the full range of radiance (Lmin, Lmax)

Output: 0,1 or the full range of reflectance (computed by dividing Lmin and Lmax by the factor that converts radiance to reflectance and is computed by i.landsat.toar)

Or in case of reflectance

Input: Lmin, Lmax divided by the convertion factor mentioned above

Output: the same as radiance


In both cases the resulting values are different which cannot be correct (Radiance or reflectance should produce the same outcome) and when I examine the resulting RGB, in QGIS for example, the result is almost exactly the same as the digital number image before the atmospheric correction.

The only thing that i.atcorr is doing is shifting the histogram (that is why the output values are different) and of course a histogram shift produces the same visual result.


Does anyone really uses i.atcorr to perform atmospheric correction to Landsat? And if so, which is the right way?


Thanks in advance,

Mat
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