NASA - National Aeronautics and Space Administration

S ince launch in April of 2006, CloudSat has provided the first near-global view of the three-dimensional structure of clouds from space. CloudSat, part of NASA’s afternoon A-TRAIN constellation of satellites, fl ies a 94-GHz cloud radar that takes near-nadir measurements of the vertical structure of both cloud and precipitation systems from a sunsynchronous orbit approximately 705 km above the Earth’s surface. Observations of the variability of clouds over the surface of the Earth and through the depth of the atmosphere are creating a continually growing database that is useful for a broad range of meteorological applications, including evaluation of numerical prediction models and development of new and better convective parameterizations. Meteorological radar systems transmit a pulse of electromagnetic energy and measure the backscattered energy that is returned to the radar dish. The backscatter occurs as a result of interactions with cloud and precipitation particles, as well as intervening atmospheric gases like water vapor and oxygen. The way electromagnetic radiation interacts with these particles is dependent on the frequency of the radiation, and the type, size, orientation, and distribution of the particles. The CloudSat cloud profi ling radar (CPR) operates at 94 GHz and is therefore especially sensitive to cloud-sized particles. At this frequency, attenuation by water vapor is nonnegligible and attenuation by precipitation can be significant. In