[GRASS-user] i.atcorr: which is the meaning of range parameter?

[Markus Metz]

Hi Vero,

On Wed, Nov 13, 2019 at 12:59 PM Veronica Andreo <veroandreo at gmail.com>
wrote:
>
> Hi all,
>
> I'm using i.atcorr for atmospheric correction of Pleiades imagery. The
data comes as DN in 12 bits.

That is, values can be in the range 0, 4095, but the full possible range is
not necessarily used.

> Reading the manual of i.atcorr, I get that I must provide radiance data.
Hence I converted each band to radiance using gain and bias from the
metadata. Now, for the range parameter in i.atcorr, I assume I must pass
the min/max output of r.info for each band. There's no extra info in the
metadata about theoretical range for each band.

No, the range parameter in i.atcorr needs the theoretical range. For
example for Landsat, values can be in the range 1, 255 (0 is reserved for
nodata IIRC), but actual band values usually cover only a part of that
range. Therefore min/max of a band is not correct.

Regarding Pleiades or other imagery, you need to get from documentation or
metadata the valid range and use this as range for i.atcorr.

HTH,

Markus M

>
> In the i.atcorr manual and in some older emails, I read for example, that
the range for Sentinel 2 is 1 to 10000. However here [1] it says:
"Per-pixel radiometric measurements are provided in Top Of Atmosphere (TOA)
reflectances along with the parameters to transform them into radiances".
AFAIU, 1,10000 is TOA range.
>
> So, I'm a bit lost... What is really this range parameter representing?
>
> Thanks much in advance
>
> Vero
>
> [1]
https://earth.esa.int/web/sentinel/user-guides/sentinel-2-msi/product-types/level-1c
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