Retrieval of Cloud and Aerosol Emissivity and Particle Size in the Frame of the CALIPSO Mission

The retrieval of cloud and aerosol radiative properties at the global scale is an important challenge for the understanding of climate change. To this respect upper level clouds are of particular importance due to their contribution to radiation budget and the unknowns in their properties. The split window technique has long been applied to the data of spaceborne passive thermal imagers to retrieve the effective diameter of the ice particles in such clouds. This method has been improved in the frame of the CALIPSO mission, developed in collaboration between NASA and CNES, by combining the CALIOP lidar information and the Infrared Imaging Radiometer (IIR) data. IIR measurements are performed in the thermal infrared using three spectral bands (8.70, 10.65 and 12,05 μm). The IIR operates at room temperature and has been designed to meet the high sensitivity performance required. The backscatter lidar data are used as inputs to the IIR inversion algorithm to select analysis cases and improve retrievals with a better knowledge of the cloud parameters required for the inversion of the radiometry data. This new algorithm developed in France by the IIR-WG is run at the NASA LaRC Atmospheric Data Sciences Center for the analysis of space measurements. Results are archived at the Center ICARE in Lille (joint effort from CNES-CNRS-University of.Lille and Région Nord). The algorithm is described and results from sensitivity studies are discussed in terms of trade-offs performed. First results from level 1 data validation and level 1 statistics are presented. Synergies between lidar and IR radiometer instruments are discussed in the frame of the algorithm development and case studies performed.