20020711: SSEC, CSU 4 km visible calibration

>From: Darren Gallant <address@hidden>
>Organization: UCAR/JOSS
>Keywords: 200207111918.g6BJIGa29261 McIDAS AREA calibation

Darren,

>What exactly is a pre-calibrated image?

An image that has a specific -- fixed -- conversion from brightness
counts to a calibrated unit.  For instance, the IR and WV images in
the Unidata-Wisconsin datastream have a fixed, two slope, linear
relationship between brightness values and temperature.

>I know Tom discussed this with me
>before, but I can't recall the specifics. Both the SSEC and CSU data have
>calibration blocks. Are they used when the image is displayed?

The display is simply a mapping of internal "raw" counts to values
that can range from 0 to 255.  When you interrogate the image using
IMGPROBE, the calibration block -- if it exists -- is used to convert
the raw counts to calibrated values like temperature, radiance, albedo,
etc.

Tom