【作者】 杨超；

【导师】 郭立新；

【作者基本信息】 西安电子科技大学 ， 无线电物理， 2010， 博士

【摘要】 本论文就海上大气波导中电磁波传播及反演问题中的有关关键技术开展了系统的研究。重点研究了海面电磁散射模型和大气波导的传播模型,利用学习算法研究了典型大气波导(蒸发波导和表面波导)中的反演问题,对GPS信号的散射特性和传播特性及利用GPS信号反演大气波导进行了研究。论文主要工作如下:1.研究了粗糙(海)面电磁散射的小斜率近似方法和修正基尔霍夫近似方法。在极坐标系下推导了小斜率近似方法的散射系数计算公式。基于高斯介质粗糙面和粗糙海面,将得到的数值结果与实验测量数据和基尔霍夫近似方法计算结果进行了对比分析。同时还讨论了入射波频率、风速对海面电磁散射特性的影响。为了研究大入射角电磁散射问题及提取散射场信息,利用修正基尔霍夫近似方法分析了粗糙海面的电磁散射特性。2.研究了大气波导传播的抛物方程模型及其常见的窄角抛物方程和宽角抛物方程的推导,给出了抛物方程求解的方法及关键步骤。为验证抛物方程模型的准确性,将其数值模拟结果和实验数据、模理论结果以及AREPS的结果进行了对比。利用改进离散混合傅立叶方法研究了海面粗糙度对大气波导中电磁波传播的影响。3.基于抛物方程和麦克斯韦方程组推导了射线传播所满足的程函方程。利用一种便捷的射线追踪方法研究了典型的大气波导环境中(蒸发波导和表面波导)电磁波的超视距传播轨迹。将射线追踪方法的结果与抛物方程的改进离散混合傅立叶方法得到的传播损耗分布图、AREPS的结果进行了比较分析,验证该模型的准确性。讨论了天线位置与能否形成大气波导之间满足的关系。4.针对大气波导中传播损耗和折射率剖面与其影响因素之间存在的复杂非线性关系,利用神经网络和最小二乘支持向量机方法分别预测了大气波导环境中的电磁波传播损耗和折射率剖面。对于折射率剖面的反演,为了减少训练样本数量并且能体现一般性,利用拉丁超立方抽样方法对训练折射率参数进行抽样,并对表面波导的反演结果进行了统计分析。5.利用截止波长的概念分析了L波段GPS信号发生大气波导传播的可行性。基于修正基尔霍夫近似理论分析了GPS散射信号的极化和散射特性,并讨论了风速和入射角对极化率和双站散射系数的影响。研究了GPS信号大气波导传播的初始场,包括平面波初始场与本文提出的以GPS信号散射场作为初始场。利用抛物方程方法分析了蒸发波导中GPS信号的传播特性,讨论了蒸发波导高度和GPS仰角对其传播特性的影响。最后,利用GPS散射信号反演了蒸发波导折射率剖面。更多还原

【Abstract】 In this dissertation, the key techniques related to electromagnetic wave propagation and inverse problem in the marine atmospheric duct are systematically investigated. Emphasis is put on studying the electromagnetic scattering model of rough sea surface and the forward propagation model of atmospheric duct, the inverse problem related to the typical atmospheric duct (evaporation duct and surface duct) is examined using the learning algorithm. The GPS signal scattering properties, propagation properties and the inversion of atmospheric duct using GPS are also studied. The main works are as follows:Firstly, the rough (sea) surface electromagnetic scattering theory is investigated, which includes the Small Slope Approximation (SSA) and modified Kirchhoff Approximation. The scattering coefficient of rough (sea) surface by the SSA is derived in the polar coordinate. Based on the Gaussian dielectric rough surface and rough sea surface, the numerical results are compared with the experimental data and those by Kirchhoff Approximation. In addition, the effects of incident wave frequency and wind speed on the electromagnetic scattering properties of rough sea surface are also investigated. To study the electromagnetic scattering of large incidence and extract the scattering field information, the electromagnetic scattering from rough sea surface is analyzed using the modified Kirchhoff Approximation.Secondly, the parabolic equation for atmospheric duct propagation and the derivation of the common used narrow-angle and wide-angle parabolic equation are investigated, and the key steps in solving parabolic equation are presented. To validate the accuracy of the parabolic equation for atmospheric duct propagation, the numerical simulations are compared with the experimental data, the results of Mode theory and the AREPS model. The Improved Discrete Mixed Fourier Transform (IDMFT) is used to analyze the influence of the sea surface roughness on the electromagnetic wave propagation in atmospheric duct.Thirdly, the Eikonal equation satisfied by the ray propagation is derived based on the parabolic equation and Maxwell’s equations. A convenient Ray Tracing Approach is used to intuitively simulate the over-the-horizon propagation path in typical ducting environment (evaporation duct and surface duct). The ray tracing results are compared with the propagation loss distribution map of parabolic equation model rigorously solved with IDMFT and the AREPS. The relation between the antenna position and the formation of the atmospheric duct is discussed. Fourthly, according to the complex nonlinear relation among the propagation loss, the refractivity profile and its influence factor, the RBF Neural Network (RBFNN) and Least Square Support Vector Machine (LSSVM) are used to predict the propagation loss and refractivity profile in the atmospheric duct, respectively. To reduce the number of sampling and reflect the generality, the Latin hypercube sampling method is adopted to sample refractivity parameter, and the statistical analysis for the inversion results of surface duct are presented.Fifthly, the concept of cut-off wavelength is used to analyze the feasibility of GPS signal propagation in the atmospheric duct. The polarization and scattering properties of GPS scattering signal are discussed using the modified Kirchhoff Approximation, and the influence of wind speed and incident angle on the polarizability and bistatic scattering coefficient are investigated. In addition, the initial field of GPS, such as the initial field of plane wave and the GPS scattering field proposed in this work are investigated. The parabolic equation model is used to analyze the GPS signal propagation properties in the evaporation duct, and the influence of evaporation duct height and the elevation angle of GPS on the propagation properties are discussed in detail. Finally, the evaporation duct refractive index profile is inverted by the GPS scattering signal.更多还原