雨滴的电磁衰减计算

摘要

Electromagnetic attenuation caused by raindrops includes both its amplitude (energy) and polarization. For calculating the amplitude attenuation of raindrops scattering,with Rayleigh approximation,using the single particle scattering and absorption cross section,combined with the sizes distribution of raindrops,the equations were established for the total scattering and absorption cross section per unit volume in scattering region. Simulation results show that the longer the wavelength,the greater the rainfall,raindrops scattering and absorption cross sections are larger. For calculating the electromagnetic polarization of raindrop,using Mie theory to determine the two perpendicular polarization components in far field,the amplitude of field strength was determined by the Bessel functions,the angle dependence function determined by the Legendre function;and the concept of degree of polarization was introduced. Polarization simulation of raindrop scattering reveals that with the scattering angle increases,all the polarization components are reduced;the reduced speeds are different,some positions on the fully polarized. The simulation results provide important parameters for correcting the impact of rainfall to communication.%雨滴的电磁衰减体现在雨滴散射的幅值(能量)和极化两方面.为计算雨滴散射的振幅衰减,借助瑞利近似,利用单粒子的电磁散射截面和吸收截面,结合雨滴的尺寸分布,建立散射区单位体积的总散射截面和总吸收截面方程.模拟结果表明电波波长越长,降雨量越大,雨滴电磁散射截面和吸收截面就越大.为计算雨滴的电磁极化效应,引入极化度的概念,利用Mie理论确定粒子散射远场的两相互垂直极化分量,其中场强的幅值由贝塞尔函数确定,角度依赖函数由勒让德函数确定,通过对不同尺寸雨滴散射场的极化模拟,发现随散射角的增大,两极化分量均减弱,但减弱快慢不同,且此消彼长,部分散射位置出现完全偏振光.模拟结果为修正降雨给通信造成的影响提供重要参数.