Launched in April 1999, the Landsat-7 ETM+ instrument is in its fourth year of operation. The quality of the acquired calibrated imagery continues to be high, especially with respect to its three most important radiometric performance parameters: reflective band instrument stability to better than ±1%, reflective band absolute calibration to better than ±5%, and thermal band absolute calibration to better than ± 0.6 K. The ETM+ instrument has been the most stable of any of the Landsat instruments, in both the reflective and thermal channels. To date, the best on-board calibration source for the reflective bands has been the Full Aperture Solar Calibrator, which has indicated changes of at most –1.8% to –2.0% (95% C.I.) change per year in the ETM+ gain (band 4). However, this change is believed to be caused by changes in the solar diffuser panel, as opposed to a change in the instrument's gain. This belief is based partially on ground observations, which bound the changes in gain in band 4 at –0.7% to +1.5%. Also, ETM+ stability is indicated by the monitoring of desert targets. These image-based results for four Saharan and Arabian sites, for a collection of 35 scenes over the three years since launch, bound the gain change at –0.7% to +0.5% in band 4. Thermal calibration from ground observations revealed an offset error of +0.31 W/m2 sr um soon after launch. This offset was corrected within the U. S. ground processing system at EROS Data Center on 21-Dec-00, and since then, the band 6 on-board calibration has indicated changes of at most +0.02% to +0.04% (95% C.I.) per year. The latest ground observations have detected no remaining offset error with an RMS error of ± 0.6 K. The stability and absolute calibration of the Landsat-7 ETM+ sensor make it an ideal candidate to be used as a reference source for radiometric cross-calibrating to other land remote sensing satellite systems.
Department, Program, or Center
Chester F. Carlson Center for Imaging Science (COS)
Brian L. Markham, John L. Barker, Julia A. Barsi, Ed Kaita, Kurtis J. Thome, Dennis L. Helder, Frank D. Palluconi, John R. Schott, Pat Scaramuzza, "Landsat-7 ETM+ radiometric stability and absolute calibration", Proc. SPIE 4881, Sensors, Systems, and Next-Generation Satellites VI, (8 April 2003); doi: 10.1117/12.462998; https://doi.org/10.1117/12.462998
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