小旋转椭球粒子群降水区雷达回波衰减订正模拟实验

Attenuation Correction to Radar Observations of Reflectivity Factor from Precipitating Area with Poly-disperse Small Spheroid Raindrops

计算了降水区雨滴形状和雨滴群旋转轴相对于雷达波偏振方向不同取向情况下的Z I关系和k I关系 ,并用 5种衰减订正算法进行雷达回波衰减订正效果研究。结果表明 ,在已知小旋转椭球粒子群取向的情况下 ,雨强越大 ,降水区回波衰减的可订正厚度越小 ;雨强 80mm/h均匀分布时 ,使用R2或R3订正法 ,5 .6cm雷达回波可订正厚度在 12 0km以上 ,3.2cm雷达可订正厚度为 5 0km左右 ;雷达遥感降水时 ,有必要正确估计小旋转椭球粒子群的取向 ,以便选用正确的k Z关系 ,提高衰减订正效果。

The relationship between attenuation coefficient, k, and radar reflectivity factor, Z, as well as that between k, Zand rainfall rate, I, is influenced by the shape of precipitating raindrops and the orientation of their rotatory axes respect to the polarization direction of the incident radar wave. Provided that the orientation of rotatory axes of poly-disperse small spheroid particles is known, correctable thickness of radar echo for attenuation depends mainly on rainrate. The heavier the rainfall rate, the thinner the correctable thickness. For an 80mm/hour precipitation uniformly distributed along a radial direction, correctable thickness of radar echo is more than 120km for 5.6cm wavelength and about 50km for 3.2cm if correction algorithm R2or R3is used. Orientation information is critically important during attenuation correction. Right k-Zrelationship must be coupled with right orientation status.