Comparison of the Minimum Bounding Rectangle and Minimum Circumscribed Ellipse of Rain Cells from TRMM

Abstract

Based on the TRMM dataset, this paper compares the applicability of the improved MCE (minimum circumscribed ellipse), MBR (minimum bounding rectangle), and DIA (direct indexing area) methods for rain cell fitting. These three methods can reflect the geometric characteristics of clouds and apply geometric parameters to estimate the real dimensions of rain cells. The MCE method shows a major advantage in identifying the circumference of rain cells. The circumference of rain cells identified by MCE in most samples is smaller than that identified by DIA and MBR, and more similar to the observed rain cells. The area of rain cells identified by MBR is relatively robust. For rain cells composed of many pixels (N > 20), the overall performance is better than that of MCE, but the contribution of MBR to the best identification results, which have the shortest circumference and the smallest area, is less than that of MCE. The DIA method is best suited to small rain cells with a circumference of less than 100 km and an area of less than 120 km², but the overall performance is mediocre. The MCE method tends to achieve the highest success at any angle, whereas there are fewer “best identification” results from DIA or MBR and more of the worst ones in the along-track direction and cross-track direction. Through this comprehensive comparison, we conclude that MCE can obtain the best fitting results with the shortest circumference and the smallest area on behalf of the high filling effect for all sizes of rain cells.

摘 要

本文结合TRMM数据集对比了改进的长轴优先最小外接椭圆(minimum circumscribed ellipse, MCE)、 长轴优先最小外接矩形(minimum bounding rectangle, MBR)、 以及根据卫星轨道坐标的直接索引区域(direct indexing area, DIA)这三种方法对雨团拟合的适用性. 发现这三种方法都能够反映云的几何特征, 从几何上逼近雨团的真实情况, 其中MCE识别雨团周长的效果具有压倒性优势, 绝大多数样本用MCE识别出的雨团周长比DIA和MBR识别出的雨团周长短, 更贴近于真实雨团. MBR识别的雨团面积较稳健, 对较多数量像元(N>20)组成的雨团, 总体表现优于MCE, 但对于最佳识别结果的贡献少于MCE. 对于周长小于100km、 面积小于120km2的小雨团, DIA有一定优势, 但总体表现平庸. MCE在任意方向获得最佳识别结果的概率较明显, 而DIA或MBR获得最佳识别结果的概率不明显, 而在沿轨道方向和跨轨道方向上的获得最差识别结果的概率较多. 综合比较, 对各种尺寸的雨团, MCE都更容易获得周长最短且面积最小的最优拟合结果.