Measurements and implications for combined radar-passive microwave rainfall profiling techniques

An upcoming NASA satellite platform, the Tropical Rainfall Measuring Mission (TRMM), represents the first opportunity to incorporate both multifrequency passive microwave and active radar measurements in its retrieval algorithms. The TRMM microwave imager (TMI) includes many of the same passive channels as the current Special Sensor Microwave Imager (SSMI), with the addition of a 10.7 GHz channel. The 14 GHz incoherent precipitation radar (PR) scans an across-track swath width about one-third the width of the forward-view conical TMI scan. Therefore, the radar data arrives about a minute after the TMI scan, and the PR and TMI beams view significantly different profiles in the atmosphere for a given on-Earth pixel location. During the 1992-1993 TOGA-COARE experiment in the western Pacific Ocean, a DC-8-based precipitation radar and an ER-a-based 4-channel microwave radiometer gathered data over a multitude of precipitating storm regions including the forming and mature stages of a tropical cyclone. Example imagery and vertical radar profiles are presented. These data are currently being used by the authors for vertical profiling algorithms which exploit the information contained in both the radar and radiometer. The radar data provide clues to the underlying cloud vertical structure that can be used to mitigate ambiguities in profile-based retrieval algorithms that rely upon the passive T_B alone