Detector Dependency of MODIS Polarization Sensitivity derived from on-orbit Characterization

Scanning radiometers on earth-orbiting satellites are used to measure the chlorophyll content of the oceans via analysis of the water-leaving radiances. These radiances are very sensitive to the atmospheric correction process, which in turn is polarization dependent. The image created by a scanning radiometer is usually composed of successive scans by two mirror sides and one or several detectors. The Moderate Resolution Imaging Spectroradiometer (MODIS) has 10 detectors for each ocean color band. If the polarization sensitivities are different among detectors and this is not taken account of in the atmospheric correction process, striping will occur in different parts of the images. MODIS polarization parameters were derived using ground truth data from another earth-orbiting sensor (Sea-viewing Wide Field-of-view Sensor, SeaWiFS), allowing a comparison of the on-orbit characterization and the prelaunch characterization. This paper presents these comparisons for the MODIS instruments on the Aqua and Terra satellites. The detector dependency is clearly different in the prelaunch characterization. This paper also describes the detector dependency of the vicarious corrections to the radiometric calibration coefficients. During the first four years of each mission, the only correction needed to minimize striping in the ocean color products is a constant offset, there is indication of a temporal trend or a view angle dependency for these offsets. The offsets are similar for both instruments, but larger in Terra.