Use of CALIOP Cloud Data for VIIRS and MODIS Cloud Mask Validation

Cloud characterization data from the CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) on board the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) space platform is utilized to assess the effectiveness of the future VIIRS (Visible/Infrared Imager Radiometer Suite) and current MODIS (Moderate Resolution Imaging Spectroradiometer) cloud masks. This is accomplished in three ways: 1) validate existing cloud test thresholds, 2) evaluate possible improvements to thresholds or to the form of threshold tests, and 3) comparisons of imager cloud mask data to that of CALIOP. The nadir-viewing, active sensor CALIOP yields very accurate data concerning the spatial and vertical locations of clouds as it orbits the Earth. The CALIPSO platform is part of NASA’s “A-train” constellation of polar orbiting satellites that fly in close formation and that also includes Aqua. CALIPSO-CALIOP lags Aqua-MODIS by just 75 seconds and thus views the same Earth scenes at very nearly the same time. Match-ups between the CALIOP, VIIRS, and MODIS data sets have been created and analyzed in this validation exercise. Match-ups include cloud mask results from the three data sets, geo-location data, MODIS reflectances and brightness temperatures and some ancillary data. VIIRS results are generated from MODIS proxy radiance and geo-location data so that differences between those two are entirely due to the algorithms.