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Multiple Scattering Effects of Electromagnetic Waves from Randomly Distributed Particles and Its Application to a High Precision Radar

随机分布粒子电磁波的多重散射效应及其在高精度雷达中的应用

基本信息

批准号：
08650515
负责人：
ITO Shigeo
金额：
$ 1.41万
依托单位：
Toyo University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-08650515/
关键词：
RANDOM MEDIA RADAR ELECTROMAGNETIC SCATTERING RAIN MILLIMETER WAVES MULTIPLE SCATTERING PROPAGATION 降雨散乱

项目摘要

For millimeter wave regions, the effects of multiple scattering in rain on radar signals may not be ignored for higher frequencies or higher rainfall rates. The theoretical estimation of rainfall rate has been based on the conventional polarimetric radar equation, which only takes account of the first-order scattering contribution. However, air-borne radar measurements of rain have shown very high depolarization ratios at 34.5GHz and suggested that the multiple scattering is included. The purpose of this paper is to clarify the effects of multiple scattering on radar signals in the time domain and to apply to the development of the radar systems with higher precision. To examine multiple scattering effects, the second-order solution of the radiative transfer equation was derived for the linearly polarized incident waves. Both of co-polarized and cross-polarized intensities were calculated. The theoretical results indicate a slower decrease in the co-polarized intensity against the range from the radar and a rapid increase in the linear depolarization ratio (LDR) near the rear edge of the rain layr. The laboratory measurements under controlled scattering parameters were made for simulated rain of randomly distributed spherical scatterers at 16.5GHz and 30GHz. The measured LDR is very large and is in remarkably good agreement with theoretical calculations. Therefore, the conventional radar equation may overestimate the rainfall rates in view of the present analysis. The simultaneous observation of co-and corss-polarized intensity would lead to estimate the higher precise rainfall rate and would need to analyze the fine structure of rain. We will further examine an alternative approximate solution of the radiative transfer equation and consider to treat the case of the nonspherical raindrops. The similar experiment should be done for various kind of size parameters of the raindrops.

对于毫米波区域，在较高的频率或较高的降雨率下，雨中多次散射对雷达信号的影响可能不可忽略。传统的极化雷达方程仅考虑了一阶散射的贡献，而对降雨率的理论估计是基于此。然而，机载雷达对降雨的测量显示，在34.5GHz处有非常高的去极化率，并表明多次散射也包括在内。本文的目的是从时域上阐明多次散射对雷达信号的影响，为研制高精度雷达系统提供理论依据。为了研究多次散射效应，推导了线偏振入射波辐射传输方程的二阶解。计算了共偏振和交叉偏振强度。理论计算结果表明，在雨层后缘附近，共偏振强度随雷达距离的减小而减小，线性退偏振比（LDR）随距离的增大而迅速增大。在16.5GHz和30GHz频率下，对随机分布的球形散射体模拟雨进行了受控散射参数的实验室测量。测得的LDR是非常大的，是非常好的协议与理论计算。因此，传统的雷达方程可能高估了降雨率鉴于目前的分析。同时观测同偏振和交叉偏振强度将导致更高精度的降水率估计，并需要分析雨的精细结构。我们将进一步研究辐射传输方程的另一种近似解，并考虑处理非球形雨滴的情况。对于雨滴的各种尺寸参数，应进行类似的试验。