Keynote: Towards "unified" radar/lidar/radiometer retrievals for cloud radiation studies

The synergy of remote-sensing instruments offers the potential for accurate retrievals of cloud properties, essential if we are to understand their important role in the radiation budget. In this talk a "unified" retrieval scheme is described that uses a variational approach to combine cloud radar, backscatter lidar and both infrared and microwave radiometers, to retrieve the properties of liquid, ice and mixed-phase clouds. The rigorous treatment of observational errors and careful use of additional constraints enables the retrieval to blend smoothly in the vertical between regions where different instruments are sensitive (for example, the common situation where the lidar is extinguished before penetrating the full depth of the cloud, while the radar cannot detect the small particles at cloud top). The scheme has been applied both to ground-based observations from the European Cloudnet project, and to spaceborne observations from the A-train of satellites. The retrievals are tested against radar-only retrievals by using them in a radiative transfer model to simulate the observed broadband top-of-atmosphere and surface fluxes. The resulting dataset is being used to evaluate the radiative forcing of various cloud types in climate models.

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