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20030221: CSU-CIRA OS-2 formatted MCIDAS area files

>From: Niles Oien <address@hidden>
>Organization: UCAR/RAP
>Keywords: 200302212035.h1LKZVt10295 McIDAS RAMSDIS CIRA GVAR


>I have some visible channel satellite data in CSU-CIRA
>OS-2 formatted MCIDAS area files.
>I can read these files OK but what I get are counts,
>specifically 16 bit counts that run from 0 to about 30,000.

If these are GVAR images, I would suspect that the data are actually
10-bit values left shifted in a 2-byte word so that the value range is
pushed from 0-1024 to 0-32768.

>I can display these data and they do look like satellite
>images, but I need to know the relationship between counts
>and the physical albedo values in order to use these
>data analytically.
>Do you know what the relation is between counts and albedo
>values for these files? I can send you a McIDAS file if that
>would help.

If they really are linearly scaled (left shifted) 10-bit values, then
albedos should be calculable in the standard manner.

The following CIRA web pages have information that will probably be of

GOES imagery displayed using different unit scales or different display systems

Conversion of GOES visible 10-bit GVAR counts into 8-bit brightness counts

Imager Calibration Coefficients (last updated 3 December 1998)

This Office of Satellite Operations (OSO) page may also be useful:

Implementation of the post-launch vicarious calibration of the GOES
imager visible channel


Please let me know if the information above was useful.

>Niles Oien, NCAR, Boulder CO

Tom Yoksas

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