Cloud feedbacks remain the largest source of uncertainty in our ability to predict the future climate (IPCC, 2007). They are also the main source of uncertainty in the present understanding of the hydrological cycle. Cloud properties are well observable from space. They need to be better understood for many purposes, including the assessments of the climate impact of aviation, ships, and other traffic modes. Model improvements can only be achieved by developing and testing new, physical parameterizations and comparing them with suitable observations. Upcoming Earth observation missions, in particular ESA EarthCARE, use novel concepts which will provide radically new insights into the role of water and ice clouds in weather and climate. Completely new methods and verification approaches are required to fully exploit this suite of active and passive instruments. Significant progress has been made at IPA concerning the development of one- and three-dimensional radiative transfer models, the remote sensing of aerosols, water and ice clouds from satellites and aircraft, the improvement of cloud and radiation parameterizations in numerical models, and the quantification of the impact of air traffic on cirrus cloudiness. New passive instruments of unprecedented quality like SEVIRI on MSG allowed for the first time to track the life cycle of clouds from space. First steps have been made towards generating realistic synthetic satellite images from the output of weather and climate models for direct comparison with real observations. This tool provides a very powerful novel method to test and improve predictive models as well as to develop and test cloud remote sensing algorithms.
Our objective is to develop novel cloud and aerosol retrieval methods using the synergy of active and passive remote sensing with Lidar, radar, imaging spectrometers, and in-situ observations from satellite and airborne platforms, in preparation for EarthCARE. The methods will build on the experience gained from the recently launched CALIPSO and CloudSat missions and will allow for the first time the quantitative retrieval of cloud property profiles and their impact on the radiation balance of the Earth from space.