[Datastream #IZU-822216]: Calibration of visible satellite data

Hi Ken,

re:
> I'm using visible satellite data from LDM/NOAAport, and I believe that the
> brightness values are not the raw satellite counts, but have undergone
> a calibration or transformation.

You are correct.

re:
> I need to find out how that is done
> so that I can back out the raw counts.

It is unlikely that you will be able to get the raw counts mainly because
the image pixel values contained in the GINI imagery contained in NOAAPort
has been transformed from 10-bit values to 8-bit values.  Moreover, the data
are no longer in their original satellite projections, so a one-to-one
mapping of GINI pixel to original satellite pixel does not exist.

re:
> Here is a footnote in a paper by Perez et al. (2002):
> 
> http://en.openei.org/datasets/files/673/pub/perez2002_14.pdf
> (page 4)

 "Depending on its source the value of pix may need additional corrections to
  reflect the original satellite measurement count. In the US, for instance, 
data
  available trough Unidata (2002), a quadratic correction is applied to visible
  images for better image viewing. This correction should be removed as part of
  the pixel normalization process."

To be clear: The transformations made to the original satellite scans during the
conversion to the GINI format are done by NESDIS, not Unidata.

re:
> So that's exactly what I need to do, find the quadratic correction that
> has been applied.  I can't find documentation of that on the Unidata
> site. The reference in the paper is to:
> 
> Unidata (2002): Unidata Internet Data Distribution System.
> 
> http://my.unidata.ucar.edu/

The NOAAPort imagery we distribute in the IDD NIMAGE feed are not modified by
Unidata.  Given this, we do not maintain the kind of documentation that you
are looking for.

I believe that what you are looking for is the Interface Control Document for 
AWIPS.  This can easily be found by a Google (tm) search using 'gini icd' as
the search key.  The top hit I just got using 'gini icd' as the search key
is:

[PDF] INTERFACE CONTROL DOCUMENT (ICD) FOR AWIPS - NOAA
http://www.google.com/url?sa=t&rct=j&q=gini%20icd&source=web&cd=1&cad=rja&sqi=2&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.nws.noaa.gov%2Fnoaaport%2Fdocument%2FICD%2520CH5-2005-1.pdf&ei=dyRFUKicI4jlrAG62YD4CQ&usg=AFQjCNFgEXfZbc1NORBUvmwQa_kAmJL42A

The section of the ICD that you are likely looking for is:

4.4 DEFINITION OF IMAGER CALIBRATION COEFFICIENTS ARRAYS

which starts at p 35 in the 2005 version of the ICD.

re:
> Thanks for your help!

No worries.  I hope the information above helps.

Cheers,

Tom
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Ticket Details
===================
Ticket ID: IZU-822216
Department: Support Datastream
Priority: Normal
Status: Closed