激光在准球形边界卷云中传输的衰减和透过特性

Attenuation and Transmission Characteristics of Laser Propagation in Cirrus Clouds With a Spherical Boundary

高空卷云主要由各种不同形状的冰晶粒子组成,是地空链路上激光信号传输的重要影响因素。依据高空卷云中冰晶粒子的分布特征和散射特性,采用C版本的离散纵标法(CDISORT),充分考虑地球球形曲率及云层冰晶粒子多次散射影响因素,研究准球形边界云层的激光透过率和衰减特性,并比较了太阳天顶角不同时平面平行模式和准球面模式下卷云大气激光透过率的差异,数值计算了三种激光波长(0.65,1.06和3.8μm)在卷云中传输时的衰减和透过特性。计算结果表明:较小太阳天顶角(小于80°)入射时,两种模式下卷云大气激光透过率相对误差很小,其中0.65μm激光波长入射时两种模式下的相对误差仅为1.72%,较大太阳天顶角(大于80°)入射时,两种模式下卷云大气激光透过率相对误差明显增大,0.65μm激光波长入射时两种模式下的相对误差最大达到69%;卷云粒子单次散射时,激光在云层的衰减与卷云粒子有效半径、传输距离、光学厚度及激光波长等因素有关,随光学厚度的增加,云层的激光透过率减少,1.06μm激光波长入射时透过率最大,3.8μm激光波长入射时透过率最小;0.65和1.06μm激光波长入射时,随云层粒子有效半径的增加激光透过率逐渐增加,而3.8μm波长激光,随云层粒子有效半径的增加激光透过率逐渐减少,随相对方位角的增加,云层的激光透过率减少,且不同卷云传输模型对激光透过率也存在不同的影响。该研究工作将为开展地空链路星载、机载激光通信、激光雷达探测等工程系统中的激光信号云层传输特性的应用提供理论支持,同时也可进一步拓展为地空链路激光遥感、制导和预警等应用提供预先理论研究基础。

An altitude cirrus cloud is mostly composed of ice particles,which affects laser signal transmission over ground to air links.Basing on,the distribution and scattering characteristics of ice crystal particles in high altitude cirrus cloud sand by cirrus clouds considering the spherical curvature of the Earth and multiple scattering,the laser transmission and attenuation characteristics of spherical boundary clouds,are studied in this paper using the spherical model of the discrete ordinate method(CDISORT).The laser transmittance differences between the plane-parallel model and the quasi-spherical model in the ice cloud atmosphere under different solar zenith angles are compared.The laser signal propagation’s attenuation and transmittance characteristics are compared through cirrus clouds at three wavelengths(0.65,1.06,3.8μm)are calculated numerically.The results show that when the solar zenith angle is small,the relative error of the laser transmittance between the two models is very small when the solar zenith angle is less than 80°,the relative error between the two models at the laser wavelength of 0.65μm is only 1.72%when the radiation transfer equation of the spherical atmosphere is calculated according to the plane-parallel atmosphere model,however,when the solar zenith angle is greater than 80°,the relative error of the laser transmittance between the two models in the ice cloud atmosphere increases,the relative error between the two models at the laser wavelength of 0.65μm is 69%;The laser attenuation caused by propagation through the clouds is related to the effective radius,transmission distance,and laser wavelength when a single scattering of a cirrus cloud is considered,as the optical thickness increases and the laser transmittance’s change with the cloud layer decreases,the maximum transmittance is achieved at the laser wavelength of 1.06μm and the minimum transmittance is achieved at the laser wavelength of 3.8μm;The laser transmittance at the wavelengths of 0.65 and 1.06μm increases with the effective radius of cloud particles,but at the wavelength of 3.8μm,it does not increase under the same constraints,the laser transmittance of cloud decreases with the increase of relative azimuth,and different cirrus dispersion models have different effects on the laser transmittance.The results of the characteristics of laser transmission through cirrus clouds presented in this works provide an important theoretical basis for engineering applications,including ground-to-air link satellite-borne,airborne laser communication,laser radar detection,at the same time,it can lay a research foundation for the application of laser remote sensing,guidance and early warning of ground to air link.