[GRASS-user] More i.atcorr doubts

[Daniel Victoria]

Hi list,

I'm still struggling with i.atcorr as there are some steps that I'm
not understanding very well. It concerns mainly how to treat the
output.

1) I'm using input in radiance, following landsat transformation rules
(Qmin, Qmax, etc). But from what I read in the manual, i.atcorr has an
input range which, defaults to 0 to 255. As I see, this is basically
transforming the radiance values back to DN. This now takes me to
another question. My radiance transformation parameters are a bit
messed up and I get negative radiances (I know this is wrong). So, is
the range parameter in i.atcorr important? Would this mean that it's
not necessary to use radiance values and that I could use the raw DNs?

2) Output is scaled from 0 to 255. I was under the impression that, to
convert it back to reflectance, all I needed to do was divide by 255.
But, because of that range parameter, I started thinking: If i.atcorr
input radiance is scaled from 0-255 (similar to what DN values are)
then, shouldn't the conversion from i.atcorr output to reflectance use
the same transformation parameter as the DN-Radiance conversion
formula?

Cheers and hoping to get a better understanding of i.atcorr :)

Daniel