Comparison of Airborne In Situ, Airborne Radar–Lidar, and Spaceborne Radar–Lidar Retrievals of Polar Ice Cloud Properties Sampled during the POLARCAT Campaign

International audienceThis study illustrates the high potential of RALI, the French airborne radar-lidar instrument, for studying cloud processes and evaluating satellite products when we have satellite overpasses. We demonstrate, for an Arctic Nimbostratus ice cloud collected on 1 April 2008 during the POLARCAT campaign, the capability of this synergistic instrument to retrieve cloud properties and to characterize the cloud phase at scales smaller than a kilometer which is crucial for cloud process analysis. A variational approach, which combines radar and lidar, is used to retrieve IWC, extinction and effective radius. We show that the combination of radar and lidar provides better retrievals than stand-alone retrievals, and that in general the radar overestimates and the lidar underestimates IWC. As the sampled ice cloud was simultaneously observed by CloudSat and CALIPSO satellites, we show a new way to assess satellite cloud products by combining in-situ and active remote sensing measurements. It was then possible to compare RALI to three satellite ice cloud products: CloudSat, CALIPSO and DARDAR