A comparison of ISCCP land surface temperature with other satellite and in situ observations

Abstract

Land surface skin temperature (LST) estimates from the International Satellite Cloud Climatology Project (ISCCP) are compared with estimates from the satellite instruments AIRS and MODIS, and in situ observations from CEOP. ISCCP has generally slightly warmer nighttime LSTs compared with AIRS and MODIS (global) and CEOP (at specific sites). Differences are smaller than 2K, similar to other reported biases between satellite estimates. Larger differences are found in the day‐time LSTs, especially for those regions where large LST values occur. Inspection of the AIRS and ISCCP brightness temperatures at the top of the atmosphere (TOA‐BT) reveals that where the LSTs differ so too do the TOA‐BT values. Area‐averaged day‐time TOA‐BT values can differ as much as 5K in very dry regions. This could be related to differences in sensor calibration, but also to the large LST gradients at the AIRS mid‐day overpass that likely amplify the impact of sensor mismatches. Part of the studied LST differences are also explained by discrepancies in the AIRS and ISCCP characterization of the surface (emissivity) and the atmosphere (water vapor). ISCCP calibration procedures are currently being revised to account better for sensor spectral response differences, and alternative atmospheric and surface data sets are being tested as part of a complete ISCCP reprocessing. This is expected to result in an improved ISCCP LST record.