Thank you Nikos & Marcus, Converting to TOA radiance (or reflectance) is not really the issue... I have already been following "Absolute Radiometric Calibration, Prepared By: Michele A. Kuester" using the formula for L (done in R, screenshot attached). I do think it is necessary that this be done in FLOAT32 to retain enough detail and per DigitalGlobe recommendations.
So, if I covert to TOA radiance as you've described, I am left with 32-bit pixels. I then import the images using r.in.gdal and launch i.atcorr. *Would the input range then be 0, 4294967295 (i.e. (2^32) - 1)? * If so, I wonder what a good output range might be, as I presume using r.out.gdal on a 32-bit image could take a long time. Thank you for your help, Paige On Wed, Apr 8, 2020 at 6:31 AM <n...@nikosalexandris.net> wrote: > 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 > -- *Paige Byassee* Appalachian State University '19 B.S., Ecology|Certificate in GIS (704)488-0872 byasseepa...@gmail.com
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