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

从空间观测降雨对于我们了解与全球变暖有关的气候变化是必不可少的;特别是，通过星载雷达观测降雨非常重要，因为雷达直接高精度地定性测量降雨的三维结构。然而，在热带降雨测量使命（TRMM）降水雷达（PR）观测降雨的情况下，在极少数情况下，在西藏和安第斯山脉等高山地区，强地面回波可能被误判为强降雨回波，这仍然是一个工程问题，尽管发生这种误判的频率很低。本研究的目标是高精度地分离降雨回波和地面回波，为了实现这个目标，我们需要一个可靠的地面高程图。因此，我们利用TRMM PR数据制作了一幅数字高程图。在2002财政年度进行初步研究后，我们得出的结论是， ...更多信息 2km x 2km网格。在2002和2003财年，我们使用1998年2月和9月的TRMM PR数据生成了地表高程图。1998.我们注意到，如果我们使用所有49个天线波束方向的PR数据，则不到一个月的数据覆盖了整个观测纬度范围。在2004财政年度，我们将这样获得的地表高程图与SRTM 30进行了比较航天飞机雷达地形使命数字高程模型，水平网格间距为30弧秒（约1 km）），据称是最精确的1 km DEM。在富士山及其周边地区，SRTM 30显示出较大的高程变化，有些高程高于8500 m，但SRTM PR地表高程图平滑，且趋于追踪SRTM 30的底线。这意味着SRTM 30的高程数据不是1 km × 1 km网格的平均值，而是每个网格中的一个峰值;对于雨回波和地面回波的分离，需要两步方法：一是确定地面回波峰值的位置，二是确定地面回波的顶部。对于确定表面回波峰值的位置，使用TRMM PR高程图很有用。然而，对于表面回波顶部的确定，使用SRTM 30是有希望的，因为我们需要关于天线波束区域中的仰角变化的信息，这似乎是由SRTM 30提供的。然而，如果我们在天线波束区域中使用仰角的中值，则有可能仅使用SRTM 30就足够了。一个问题是将我们的结果应用到当前的TRMM PR标准算法。少

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