A study on determination of the surface echo top for an space-borne precipitation raday by suing digital elevation map

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Observation of rain from space is indispensable for out understanding of climate change, which is related to global warming; in particular, observation of rain by a space-borne radar is very important because the radar directly measure the 3D-structure of rain qualitatively with high precision. In the case of observation of rain by the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), however, a strong surface echo can be misjudged as a strong rain echo over high mountain regions such as Tibet and Andes in a very rare cases, which remains to be an engineering issue though the frequency of the occurrence of such a misjudgment is very low. The goal of this study is to separate the rain echo and the surface echo in high precision; to achieve this goal, we need a reliable surface elevation map. Hence, we have generated a digital elevation map by using the TRMM PR data.After a preliminary study in FY2002, we concluded that we should generate a surface elevation map with a … More 2km x 2km grid. In FY2002 and FY2003, we have generated the surface elevation map using the TRMM PR data of Feb. 1998 and Sept. 1998. We have noticed that less than about one month of data covers the entire observation latitude range if we use the PR data of all the 49 antenna beam directions. In FY2004, we have compared thus obtained surface elevation map with SRTM30(Shuttle Radar Topography Mission digital elevation model (DEM) with a horizontal grid spacing of 30 arc seconds (approximately 1 km)), which is claimed to be the most accurate 1 km DEM.In and around Mt.Fuji, SRTM30 shows a large variation of elevation, and some elevations higher than 8500m, which are close to that of mountain top, but the SRTM PR surface elevation map is smooth and tends to trace the bottom line of SRTM30 in this area. This fact implies that the elevation data of SRTM30 is not an average of 1km x 1km grid but a peak in each grid.For the separation of rain echo and surface echo, two-steps approach is needed: one is the determination of the position of surface echo peak, and the other is the determination the surface echo top. For the determination of the position of surface echo peak, the use of the TRMM PR elevation map is useful. For the determination of the surface echo top, however, the use of SRTM30 is promising because we need information about the variability of elevation in the antenna beam area which seems to be provided by SRTM30. There is a possibility, however, that the use of SRTM30 alone maybe sufficient if we use median value of elevation in the antenna beam area. An issue is apply our results to the current TRMM PR standard algorithm. Less