Calibration Changes to Terra MODIS Collection-5 Radiances for CERES Edition 4 Cloud Retrievals

Previous research has revealed inconsistencies between the Collection 5 (C5) calibrations of certain channels common to the Terra and Aqua Moderate Resolution Imaging Spectroradiometers (MODISs). To achieve consistency between the Terra and Aqua MODIS radiances used in the Clouds and the Earth’s Radiant Energy System (CERES) Edition 4 (Ed4) cloud property retrieval system, adjustments were developed and applied to the Terra C5 calibrations for channels 1–5, 7, 20, and 26. These calibration corrections, developed independently of those used for the later MODIS Collection 6 (C6), ranged from −3.0% for channel 5 to +4.3% for channel 26. For channel 20, the Terra C5 brightness temperatures were decreased nonlinearly by 0.55 K at 300–10 K or more at 220 K. The corrections were applied to the Terra C5 data for CERES Ed4 and resulted in Terra–Aqua radiance consistency that is as good as or better than that of the C6 data sets. The C5 adjustments led to more consistent Aqua and Terra cloud property retrievals than seen in the previous CERES edition. After Ed4 began processing, other calibration artifacts were found in some corrected channels and in some of the uncorrected thermal channels. Because no corrections were developed or applied for those artifacts, some anomalies or false trends could have been introduced into the Ed4 cloud property record. Thus, despite the much improved consistency achieved for the Terra and Aqua data sets in Ed4, the CERES Ed4 cloud property data sets should be used cautiously for cloud trend studies due to those remaining calibration artifacts.