[GRASS-user] i.atcorr with Landsat 8

[Nikos Alexandris]

Micha:

> When doing atmospheric correction with i.atcorr on LandSat 8 images (after
> i.landsat.toar), is it correct to set range="0,65535"?RADIANCE_MAXIMUM_BAND_3

Nikos:

> After i.landsat.toar you will have either Radiance or Reflectance. For
> both the 16-bit range suggested above is not valid I think.

Micha:

> So, do I need to read the Min and Max radiance for each band separately
> from the MTL file, and use those as the range= parameter?

Micha, I now see what the concern is.

If I understand it correctly, in the case of spectral radiance (default
input type for i.atcorr) as input, I would simply use the min, max values of the
images themselves.

For reflectances (-r flag for i.atcorr) I think I would use [0, 1.0]. In
addition, (as I have done in the past) one can flatten, all values > 1.0
to 1.0 (as they normally are --should be, imho-- erroneous large
outliers).

I have to look closer at what I did in my script (see:
https://github.com/NikosAlexandris/i.landsat.atcorr/blob/master/i.landsat.atcorr.py#L371)
and fix it (currently broken). But, I do read the min and max values
from the images that are going to be processed.


At least in the case of Landsat8 imagery, the script worked well (before
it went broken :-p).

> The default of "0,255" seems to be too small.

I agree.  Furthermore, I think the current default 8-bit range for the output spectral
reflectances (i.atcorr *always* delivers reflectances) is (was) like a standard
for which many modules would simply do their job while they would fail
in case of floating point numbers or larger ranges. I think we should
communicate and maybe ask for it to change that the "normal" range for
reflectance is zero to one. And depending on how rich was the input,
simply rescaling to 8-bit comes with cost of loosing fine radiometric
details.


> I'm getting some radiance values > 600 . And the values of
> RADIANCE_MAXIMUM_BAND_x in the metadata seem to also show these high numbers.

Yes, quite expected.

[rest deleted]

Nikos