The infrared channels are calibrated in flight by using the measurements from the blackbody and the space view to generate a two-point linear calibration expression:
and
where Gi is the gain (radiance per digital count) of Channel "i," 
is the calibration intercept of Channel "i," 
and 
are the calculated physical radiances
of space and the internal blackbody calibration target at temperature T, and 
and 
are the output from Channel "i" when the instrument's field of view
is filled by the space view or by the blackbody target (Lauritson et al. 1979). The resultant linear expression relating the digital value of pixel "j" in
Channel "i" (
) to radiance (
) is:
The measurements from the infrared channels are thus converted to calibrated radiance, and these can be related to thermodynamic temperature through the Planck function modulated by the normalized spectral transfer function of each channel.
In principle this calibration scheme is perfectly adequate as the two calibration targets, the blackbody and cold space, are external to the entire radiometer. The method depends on the accurate knowledge of the blackbody calibration target temperature. The calibration coefficients for the four thermometers on the target are distributed by NOAA.
The response ranges of the detectors and digitizers are such that the signals saturate at temperatures of ~320K.
There is no in-flight calibration of the data from Channels 1 and 2.
