New in‐flight calibration adjustment of the NIMBUS 6 and 7 Earth Radiation Budget wide field of view radiometers

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Abstract
The in‐flight space environment of the NIMBUS 6 and 7 earth radiation budget instrument differs in many important ways from the steady state preflight laboratory calibration environment. Because of this, the first 20 months of NIMBUS 7 wide field of view (WFOV) channels had their calibration adjusted through a comparison with the in‐flight calibrated longwave scanner data. The adjustments were most important for the reflected solar radiation channel 13. The scanner failed on June 22, 1980, leading to the requirement for new algorithms to process the remainder of the WFOV data set. On the basis of detailed studies of the sensor characteristics, in‐flight calibration adjustments of the WFOV channels are developed which account for the major thermal, chemical, and radiative dynamics of the orbital environment. These adjustments correct for (1) long‐term changes in the rsponse of the sensors; (2) thermal transients due to the instrument's on‐off duty cycle, and (3) absorption of longwave radiation by the filter domes. In addition, these studies have led to improved in‐flight calibration adjustments for channel 12, the broadband total irradiance sensor. The rational behind the new algorithm is described, and differences between the new and old algorithms are discussed.