Recent Advances In Spaceborne Precipitation Radar Technology

Information on global, 3-dimensional distribution of clouds and precipitation are important in our understanding of global water cycle, energy budget, long-term climate variability, and short-term weather. One of the most reliable and effective means to acquire such global information is by spaceborne profiling radars. The on-going NASA/JAXA Tropical Rainfall Measuring Mission (TRMM) is the first spaceborne mission that uses a precipitation radar to acquire three-dimensional rainfall intensity field globally. In its sixth years of in-flight operations, the TRMM radar has provided exciting, new data on the 3-D rain structures for a variety of scientific applications. As a continuing effort to provide new and improved spaceborne atmospheric sensing capabilities, NASA has been developing advanced instruments and technologies for future spaceborne precipitation radars, with the over-arching objectives of making such instruments more capable and more cost effective. Two such examples are the Second-Generation Precipitation Radar (PR-2) and the Nexrad-In-Space (NIS). PR-2 is a 14/35-GHz dual-frequency, Doppler rain radar with a deployable 5-meter, wide-swath scanned membrane antenna, a dual-polarized/dual-frequency receiver, and a FPGA-based adaptive-scan control, pulse compression, and Doppler spectral processor. It is intended to provide greatly enhanced rainfall profile retrieval accuracy while using only a fraction of the mass of the current TRMM PR. NIS is designed to be a geostationary radar with the intent of providing hourly monitoring of the life cycle of hurricanes and tropical storms. It uses a 35-m, spherical, light-weight membrane antenna and Doppler processing to acquire 3-dimensional information on the intensity and vertical motion of hurricane rainfall. In this paper, an overview of the instrument design concepts and some of the key technologies developed for these advanced atmospheric radars will be presented. The research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, for the Earth-Sun System Technology Office and the Global Precipitation Measurement Mission, under contract with the National Aeronautics and Space Administration.