The operational in-orbit calibration of the GOES-8 and -9 imagers and sounders is described. In the infrared channels, the calibration is based on observations of space and an on-board blackbody. The calibration equation expresses radiance as a quadratic in instrument output. To suppress noise in the blackbody sequences, the calibration slopes are filtered. The calibration equation also accounts for an unwanted variation of the reflectances of the instruments' scan mirrors with east-west scan position, which was not discovered until the instruments were in orbit. The visible channels are not calibrated, but the observations are provided relative to the level of space and are normalized to minimize east-west striping in the images. Users receive scaled radiances in a GVAR (GOES VARiable format) data stream. The procedure users may apply to transform GVAR counts to radiances, temperatures, and "mode-A" counts is described.

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