| Detector responses in Bands 5 and 7 to the Internal Calibrator in the Landsat 5 Thematic Mapper vary over time. The observed variations are sinusoidal in nature, and believed to be caused by a time-dependent material accumulation on a window of the cold focal plane dewar containing the detectors. These changes in responses, referred to as outgassing effects, have been previously modeled, but corrections using those models were unsatisfactory. A new thin-film interference model has been developed that accounts for these effects. The model is based on analysis of three closely sampled sets of detector responses throughout the instrument's lifetime, and relates detector behavior to the accumulated material thickness, which depends on the interval since the previous outgassing event as well as the film growth rate. Corrections using this new model were found to improve the radiometric calibration of Bands 5 and 7 by approximately 3 percent. |
