Landsat cross-calibration based on near simultaneous imaging of common ground targets

The paper presents the results of an extended analysis of image data sets acquired during the tandem-orbit configuration in 1999 for the purposes of radiometric cross-calibration of the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. Earlier work focused on the tandem pair for the Railroad Valley Playa, Nevada (RVPN) site to tie down the Landsat-5 TM calibration based on the more accurate Landsat-7 ETM+ calibration. This paper describes new results based on as many as eight tandem image pairs. The additional tandem images are of primarily vegetated areas for which little or no ground reference data were available. Increasing the number of tandem pairs yielded results for the Landsat 5 TM gain coefficients within approximately ±1% of the RVPN-based results in spectral bands 1, 2, 3 and 7, and within −2% and −4% of the RVPN-based results for spectral bands 4 and 5, respectively

Radiometric cross-calibration of the Landsat-7 ETM+ and Landsat-5 TM sensors based on tandem data sets

Early in its mission, the Landsat-7 spacecraft was temporarily placed in a ‘‘tandem’’ orbit very close to that of the Landsat-5 spacecraft in order to facilitate the establishment of sensor calibration continuity between the Landsat-7 Enhanced Thematic Mapper Plus (ETM+) and Landsat-5 Thematic Mapper (TM) sensors. The key period for the tandem configuration was June 1–4, 1999, during which hundreds of nearly coincident matching scenes were recorded by both the Landsat-7 ETM+ and, in cooperation with Space Imaging/EOSAT and international ground stations, the Landsat-5 TM as well. The paper presents a methodology for radiometric cross-calibration of the solar reflective spectral bands of the Landsat-7 ETM+ and Landsat-5 TM sensors and results based on analysis of two different tandem image pairs for which ground reference data are available. With the well-calibrated ETM+ as a reference, the tandem-based cross-calibrations for the two image pairs yield TM responsivities that are consistent to each other to within 2% or better depending on the spectral band. Comparisons with independent methods and results obtained by other groups indicate that the tandem-based cross-calibration is within 3% of the independent results on average in spectral bands 1–4 but compares less favorably in bands 5 and 7. The present study indicates that the tandem crosscalibration approach can provide a valuable ‘‘contemporary’’ calibration update for Landsat-5 TM in the visible and near-infrared spectral bands based on the excellent radiometric performance of Landsat-7 ETM+. The methodology also incorporates adjustments for spectral band differences between the two Landsat sensors. Spectral band difference effects are shown to be more dependent on the surface reflectance spectrum than on atmospheric and illumination conditions. A variety of terrestrial surfaces are assessed regarding their suitability for Landsat radiometric cross-calibration in the absence of surface reflectance spectra