In-flight calibration of the EOS Multiangle Imaging Spectroradiometer (MISR)

12 The Multi-angle Imaging SpectroRadiometer (MISR) is one of five instruments on the EOS/Terra spacecraft. MISR consists of nine Earth-viewing cameras which continuously acquire global data sets in view perspectives from nadir to 70 degree(s). In order to maintain the radiometric calibration of the cameras, the instrument is equipped with an on-board calibrator. Spectralon panels, deployed at bi-monthly intervals, reflect sunlight into the cameras to be tested. This reflected light is measured by photodiode detectors which define the radiometric scale and allow the sensor calibration to be achieved. There exists six sets of four spectrally filtered photodiodes. For the first of the in- flight experiments the analysis was focused on validating the performance of the on-board calibrator components. As a result of these studies one blue-filtered, light-trapped detector was selected as the primary standard. All other on- board photodiodes have now been adjusted to be in agreement. This procedure has allowed improved band-to-band and camera- to-camera calibrations, in that all camera calibrations are traceable to a single standard. With these procedures in place MISR now plans to calibrate once every two months. New radiometric response coefficients will be delivered to the processing center following each experiment. This paper reports on these validation studies, and the post-launch radiometric response of the MISR cameras as determined during the first six months of on-orbit MISR calibration.