Landsat TM and ETM+ thermal band calibration

摘要

Landsat-5 Thematic Mapper (TM) has been imaging the Earth since March 1984 and Landsat-7 Enhanced Thematic Mapper Plus (ETM+) was added to the series of Landsat instruments in April 1999. The stability and calibration of the ETM+ has been monitored extensively since launch. Though not monitored for many years, TM now has a similar system in place to monitor stability and calibration. University teams have been evaluating the on-board calibration of the instruments through ground-based measurements since 1999. This paper considers the calibration efforts for the thermal band, Band 6, of both the Landsat-5 and Landsat-7 instruments. Initial calibration results for the Landsat-7 ETM+ thermal band found a bias error which was corrected through changes in the processing systems in late 2000. Recent results are suggesting a calibration error in gain, apparent with high temperature targets. For typical earth temperature targets, from about 5-20C, the gain error is small enough to be within the noise of the vicarious calibration process. However, for very high temperature targets (greater then 35C), Landsat-7 appears to be predicting several degrees too low. Questions remain on whether the change happened suddenly or is varying slowly, so the team will wait for another collection season before making any updates to the calibration. The calibration efforts for Landsat-5 TM considers only data collected since 1999, though there are efforts underway to extend the calibration history prior to the Landsat-7 launch. The latest data suggests that the Landsat-5 thermal band has a bias error of about 0.65K too low since 1999. Studies early in the life of Landsat-5 show that the instrument was calibrated within the error of the calibration process. It is impossible to tell, at this point, when or how the change in bias may have occurred. A correction will be calculated and implemented in the US processing system in 2006 for data acquired since April 1999.