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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

Niles,

>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
help:

GOES imagery displayed using different unit scales or different display systems
http://www.cira.colostate.edu/RAMM/cal_val/calib.htm

Conversion of GOES visible 10-bit GVAR counts into 8-bit brightness counts
http://www.cira.colostate.edu/ramm/cal_val/visible.htm

Imager Calibration Coefficients (last updated 3 December 1998)
http://rsd.gsfc.nasa.gov/goes/text/imager.calibration.html

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

Implementation of the post-launch vicarious calibration of the GOES
imager visible channel
http://www.oso.noaa.gov/goes/goes-calibration/vicarious-calibration.htm

>Thanks,

Please let me know if the information above was useful.

>Niles Oien, NCAR, Boulder CO

Tom Yoksas


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