I. Introduction
The CloudSat Mission [1] is a new satellite mission jointly developed by the National Aeronautics and Space Administration (NASA), the Jet Propulsion Laboratory (JPL), the Canadian Space Agency, Colorado State University, and the US AirForce to acquire a global data set of vertical cloud structure and its variability. Such data set is expected to provide crucial input to the studies of cloud physics, radiation budget, water distribution in the atmosphere, and to the numerical weather prediction models. Shortly after launch in late April 2006, the primary science instrument aboard the CloudSat satellite, the Cloud Profiling Radar (CPR) will begin acquiring information about the vertical cloud structure profiles by measuring the cloud backscattered power as a function of distance from the radar. The CloudSat satellite also flies as part of a constellation of satellites that also includes the EOS Aqua, EOS Aura, an aerosollidar (CALIPSO), another small satellite, PARASOL, carrying the POLDER polarimeter. Another NASA satellite, the Orbiting Carbon Observatory (OCO), will be inserted into the formation later. This constellation as depicted in Fig. 1 is referred to as the A-train. The A-Train constellation and its members.