Surface Echo Characteristics Derived From the Wide Swath Experiment of the Precipitation Radar Onboard TRMM Satellite During Its End-of-Mission Operation

The purpose of this paper is to assess the height and strength of the surface echo clutter from the wide swath operation of a future spaceborne precipitation radar (PR) using the wide swath observation data during the end-of-mission experiment of the PR onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. In this experiment, the maximum incident angle was expanded up to 32.5° from nadir, while the maximum incident angle is 18° for normal observation of the TRMM/PR. Although the results show that the clutter height monotonically increases with the incident angle as expected, the clutter height is suppressed for wide angles because of the weakening of the surface echo strength. As a result, the clutter height is less than 2 km if the rain echo is 15 dB higher than the noise level (i.e., about 34 dBZ echo for the TRMM/PR). The clutter height and the normalized backscattering cross section (0r0) are compared between ocean and land. Suppression of the clutter height is significant over ocean because of the relatively smaller 0r0 (smoother surface) and flat surface (no topography). The impact of the 0r0 for wide swath observation on the rain retrieval algorithm, especially on the surface reference technique, is also examined. The operation with a swath width almost twice the current TRMM/PR is achievable if relatively intense echoes are targeted; however, relatively weak and shallow precipitation will be masked by the clutter.