Intercomparison of ETM+, MODIS, and SeaWiFS using a land test site

The Remote Sensing Group at the University of Arizona has recently shown the successful use of a cross-comparison approach between the high spatial resolution sensor Enhanced Thematic Mapper Plus (ETM+) on the Landsat-7 platform and the 1-km footprint of the Moderate Resolution Imaging Spectroradiometer (MODIS). This work showed that these two sensors compared to better than 5% in solar reflective bands not affected by atmospheric absorption. In this paper, the work is extended to include the 1-km spatial resolution sensor SeaWiFS as part of a three-way comparison. The method described here relies on data ground-based reflectance data to estimate the surface reflectance in the MODIS and SeaWiFS bands based on surface reflectance data derived from ETM+. The cross-comparison takes into account changes in solar zenith angle due to the time separation in overpass times of the three sensors and the differing view angles between SeaWiFS and the other two sensors (MODIS and ETM+, while 40 minutes apart view the test site with the same view angle). Also included are corrections due to the spectral differences between the sensors. Results show that the at-sensor reflectance agrees to better than 4% in the solar reflective for bands not affected by atmospheric absorption and view angles out to 35 degrees.