Courtesy of Brian Markham
The Landsat Calibration Working Group held their most recent semi-annual meeting at the USGS EROS facility in Sioux Falls, SD on May 12–13, 2009. USGS/EROS Image Assessment System (IAS), NASA/GSFC LPSO, South Dakota State University, Rochester Institute of Technology (RIT), University of Arizona, and NASA/JPL calibration personnel attended the meeting. Significant progress in a number of areas of Landsat calibration was reported at the meeting:
- Continued stability is observed in the radiometric calibration of the Landsat 7 ETM+ reflective bands with no required update to the calibration.
- Continued good geometric and radiometric performance are observed for the Landsat 7 ETM+. Alignment changes and bumper wear continue to require quarterly updates to alignment and bumper parameters. A few detectors in bands 1, 2, 3 and 5 have shown increases in noise levels.
- Updates to the calibration of the thermal bands on both Landsat 5 and 7 have been developed. These gain adjustments are made possible by the long history of vicarious calibrations and the recent addition of the warm water calibration site in the Salton Sea. The calibration adjustments have very little impact on the radiometric calibration across typical water temperatures (4° C to 20° C), but will increase the derived temperature for warm targets (+1.6°C at 40° C for Landsat 7 and +1.3 ° at 40° for Landsat 5) and decrease the derived temperature for cold targets (-0.7° C at 0° C for Landsat 7 and -0.5° C at 0° for Landsat 5). The Landsat 7 updates are ready for implementation in Summer of 2009; the Landsat 5 updates are pending on the determination of the calibration stability over the 25 year mission life.
- Analysis of the recently populated Landsat 5 IAS database indicates deficiencies in the model used to correct for the ice build up on the cold focal plane window. This model adjusts the gain of bands 5 and 7 to compensate for changes in the window transmission caused by the ice. The current model is based on interpolation between a sampling of a few outgassing cycles over the mission life. The analysis indicates the need to replace this lifetime model with an outgassing interval-specific model.
- The recent extension of IAS and LPGS to include Landsat 4 TM required a flurry of activity to populate the Calibration Parameter File (CPF). With a short development schedule, the thermal band relative gain and some reflective band thresholds were updated in the first release of the operational CPF. Additional refinements to the CPF are anticipated in both the geometric and radiometric areas. In particular, the relative gain models for all detectors can be updated based on analysis of IAS data and the outgassing model for bands 5 and 7 can be modeled in a manner similar to the Landsat 5 process.