[GRASS-user] Appropriate input/output range for i.atcorr WorldView2?

[nik at nikosalexandris.net]

On 2020-04-08 15:17, Markus Neteler wrote:
..
> I believe that you need to apply the formula along with the respective
> band calibration values ABSCALFACTOR and  EFFECTIVEBANDWIDTH (the same
> is also stored in the IMD files) from the XML metadata files:
> 
> grep 'ABSCALFACTOR\|EFFECTIVEBANDWIDTH'
> 058891334020_01_P001_MUL/18DEC03184338-M2AS-058891334020_01_P001.XML
>             <ABSCALFACTOR>9.295654000000000e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>4.730000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>9.748051000000001e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>5.430000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>7.541495000000000e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>6.300000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>5.101088000000000e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>3.740000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>1.103623000000000e-02</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>5.740000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>4.539619000000000e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>3.930000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>1.224380000000000e-02</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>9.890000000000000e-02</EFFECTIVEBANDWIDTH>
>             <ABSCALFACTOR>9.042234000000000e-03</ABSCALFACTOR>
>             
> <EFFECTIVEBANDWIDTH>9.959999999999999e-02</EFFECTIVEBANDWIDTH>
> 
> Citing from "Absolute Radiometric Calibration, Prepared By: Michele A. 
> Kuester"
> https://dg-cms-uploads-production.s3.amazonaws.com/uploads/document/file/209/ABSRADCAL_FLEET_2016v0_Rel20170606.pdf
> 
>   "The top-of-atmosphere radiance, L, in units of Wμm-1m-2sr-1, is
> then found from the DigitalGlobe
>     image product for each band by converting from digital numbers
> (DN) using the equation,
> 
>     L = Gain * DN * (abscalfactor/effective bandwidth) + Offset
> 
>     The TDI specific "abscalfactor" and "effectiveBandwidth" are
> delivered with the imagery in the metadata file.
>     The digital number, DN, is the pixel value found in the imagery.
> The Gain and Offset are the absolute
>     radiometric calibration band dependent adjustment factors that are
> given in Table 1. Note that these
>     are not necessarily stagnant values and they are revisited 
> annually.
>  "
> 
> (the "Table 1" is found in the same PDF file above. You may want to
> check if a newer table version exists).
> 
> You can apply this formula with r.mapcalc, for each band to obtain TOA
> data from DN.

See also https://gitlab.com/NikosAlexandris/i.worldview.toar or 
https://github.com/NikosAlexandris/i.worldview.toar.

Maybe useful (though ratehr badly programmed at the time).

Nikos