Over time, the sensitivity of a satellite sensor can degrade, causing the current relationship between the sensor’s recorded digital count and true total radiance to differ from what was measured before launch in a stable laboratory environment. Thus, there is a need to continuously examine and adjust the sensor calibration. This can be done using a variety of methods, including solar and lunar viewing. Vicarious calibration,6 which can also be used to adjust a sensor’s calibration, is a system correction that uses in situ measurements to calculate sensor gain factors. When applied to the sensor’s values these gain factors fine-tune the results of the radiometric calibration, thereby improving the accuracy of satellite retrievals. Vicarious calibration corrects for aggregated confounding influences including the differences between the laboratory radiometric calibration and required calibration for space operations, degradation of the sensor over time, atmospheric correction errors, and geometric and environmental factors.