[GRASS-user] WV-2 top of atmosphere reflectance calculation
nik at nikosalexandris.net
Sun Jul 14 16:10:56 PDT 2013
Eric Goddard wrote:
> I looked at the i.atcorr readme you linked. I just want to be sure I
> understand this correctly: when you say band filters, are you talking
> about part F: pre-defined sensor bands of the i.atcorr man page?
Right, part F. If I got it right, we _only_ need to create a .csv file that
will contain the spectral radiance responses for each band within the sensor's
"spectral range" capabilities.
The csv file has to be structured as follows:
1) the 1st line must be a header with the Wavelength (in nm), followed by band
2) the following lines will be the actual (estimated?) spectral responses
3) if a spectral radiance response is NULL at a given wavelength, the
(line,column) should be left empty
Examples are to be found in
After preparing the .csv file, we can use the create_iwave.py script to
interpolate the "filter functions" to the "correct" step size of 2.5 nm (in
case the filter function data are delivered with a different step size).
In the PDF document you linked in your first post,
"Figure 2: WorldView-2 Relative Spectral Radiance Response (nm)" in page 3,
some "averaged band passes" in "Table 2: WORLDVIEW-2 Band Passes [nm]" in page
4 and "Table 3. WorldView-2 Effective Bandwidths" again in page 4.
We need to do some math to approximate the spectral responses at a 2.5nm step.
However, there is a note:
"Note that the actual data values used to create these plots are
available as digital files, upon request from DigitalGlobe".
I think we need to know the(se) functions/numbers from which "Figure 2" has
been derived. Then we can do some math in R or so to get what is needed.
Well, a bit more work after all than I though -- as usual :-).
> I've also posted my python script to convert WV-2 multispectral DNs
> to top of atmosphere reflectance at
> https://gist.github.com/egoddard/5989382. It is kind of messy because
> it was just meant to be a one-off script at this point :)
Nice, will check...
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