McIDAS Programmer's Manual
Version 2015

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The image source type VISR is historic in origin, going back to the early GOES satellites. At that time, data was 1-byte for both the visible and IR. Later satellites, such as GOES-6 and -7, were equipped with IR sensors that returned 10-bit values stored as two bytes. For data storage and transfer reasons, commands such as IMGCOPY can convert the 2-byte data to 1-byte. This conversion to 1-byte data preserves the temperature information for the IR channels. It is valid for GVAR, POES, Meteosat and GMS satellite data.

The image source type VISR is from word 52 of the directory block. If the area contains IR data, the temperature may be calculated from the pixel value using the formulas below, where T is the brightness temperature (degrees K) and B is the pixel value (0 to 255). For IR data, the highest pixel values correspond to the coldest temperatures.

T = 418 - B

where B >176 or B =176

T = 330 - (B / 2)

where B <176 or B = 176

The line prefix in a VISR area may be absent or it may contain only the 4-byte validity code.


The band information for GOES VISSR is provided in Appendix B, Satellite Information.

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