Vicarious calibration of MODIS using Railroad Valley Playa

The Remote Sensing Group at the University of Arizona has used ground-based test sites for the vicarious calibration of airborne and satellite-based sensors. Past work has focused on high-spatial-resolution sensors such as Landsat-7 Enhanced Thematic Mapper Plus (ETM+). Application of these methods to the Moderate Resolution Imaging Spectroradiometer (MODIS) with its lower spatial resolution poses a challenge for vicarious calibration. This work presents previous results using two vicarious techniques, the reflectance-based approach and cross-calibration to ETM+, at Railroad Valley Playa, Nevada. The modifications needed for the reflectance-based approach for application to MODIS are presented as is the method of cross-calibration to ETM+. This cross-calibration takes into account the changes in solar zenith angle due to the 40-minute separation in overpass times of the two sensors which view the test sites on the same day with the same view angle. A sensitivity study shows that these two vicarious calibration approaches, when applied to MODIS, should have uncertainty less than 5% for bands in the solar reflective not affected by atmospheric absorption. Results from these two methods agree with radiances reported by MODIS to better than 7% in the solar reflective for bands not affected by atmospheric absorption