Radar-lidar synergy for space-based retrieval of water cloud parameters

Knowledge of water clouds is very important for climate studies, but retrieval of their micro-physical properties from space is difficult and challenges the technological possibilities of today. This is partly due to the limitations of space-based instruments and partly due to physical processes in water clouds that obscure direct relationships between remote sensing observables and the cloud parameters. More specifically, the x Slarge droplet issueŠ in water clouds - just a few small drizzle droplets in water clouds may cause a radar signal that is much stronger than that of the radiatively important fraction of the cloud - makes the direct retrieval of microphysical properties with one sensor practically impossible. A new technique was developed at DUT/IRCTR that overcomes these limitations by means of sensor synergy: radar in combination with lidar can be used to classify clouds in types that contain drizzle droplets and those that do not. Appropriate retrieval algorithms can then be applied to each category to get the liquid water content profile. This technique was developed and tested with ground-based instruments. Currently, the technique is being transformed to make it suited for space-based applications. This is done with the following strategy: - test the technique with airborne radar and lidar observations (performed during the Clare98 campaign at Chilbolton), to test the performance of the technique when viewing the clouds from above; - downscale the observations to those of space-based radar and lidar; - adaptation of the technique to space based systems, e.g. to the specifications of the Cloudsat/Calipso mission or EarthCare. At the presentation we will discuss the technique and the results.