基于数值射线追踪的短波电离层传播轨迹研究

从电波传播的射线方程出发,在不考虑地磁场和碰撞的条件下,推导出了球坐标系下描述短波在电离层传输的轨迹方程.以准抛物电子密度模型为例,给出了求解参数方程组的初始条件.采用改进Euler数值方法求解轨迹参数方程组,得到短波轨迹的参数,实现了短波在电离层中的轨迹计算及仿真.仿真结果结果表明,用数值射线追踪法研究短波在电离层中的传播可以为短波天波通信的轨迹模拟和参数优选提供参考.     

Alfven波在低纬IAR中的传播研究

电离层Alfven谐振器(IAR)形成于电离层与Alfven速度极大值处之间的区域.从等离子体双流体力学方程出发,结合IRI2001模型与MSIS-E-90模型模拟了Alfven波在低纬地区IAR中的传播,得到其传播及耦合特性.根据不同时间的背景参数研究了影响IAR形成的条件,结果表明夜间电离层更适于IAR的形成,其结果与实验观测结果相吻合.     

基于抛物方程的短波电离层传播数值模拟研究

短波电离层传播损耗的计算对电离层基础研究与短波通信、天波超视距雷达等应用有重要意义，以往主要采用半经验模型.文中基于电磁波传播的抛物方程方法，实现对短波电离层传播损耗空间分布的数值计算，该方法可同时考虑电磁波传播的折射、反射、绕射和吸收等效应.根据电子浓度剖面数据，仿真计算了不同频点和天线波束宽度情况下的电离层传播损耗，从折射效应引起的传播模式、反射点高度、地面落区位置方面，与射线描迹结果进行对比，两者具有一致性.此外，进一步仿真分析了电离层的吸收效应.研究结果初步表明了抛物方程方法预测电离层传播的有效性及其强大的功能.     

非均匀电离层中VLF辐射源在海面上产生的场

为了研究甚低频(very low frequency, VLF)电磁波对电离层中目标的近场散射机制,提出了一种VLF电磁波在该环境中对有限长金属和介质柱体近场散射的计算方法。首先,通过定义散射系数和交叉散射系数,分析各向异性电离层中电型波和磁型波激励下的散射矩阵;然后,根据积分方程法和矩量法,计算得到各向异性电离层中有限长金属和介质柱体的近区散射场和表面电流半解析表达式;最后,通过各向异性电离层中VLF波的特征波分析,给出柱体近区散射场中寻常波(O波)和非寻常波(E波)分量空间分布情况。计算结果表明：电离层中VLF波在金属和介质目标表面激励了不同的电流,并在不同的电离层环境参数、柱体尺寸和入射角度下产生相应的近场散射和耦合散射;通过对比O波和E波表面电流分布和散射分量,进一步揭示了VLF波与暴露在均匀等离子体环境中的柱体目标的散射机理。本文的计算方法和结果可为电离层中散射通信和目标探测提供理论依据。

     

均匀随机媒质中传播的波有不同波数的m-n阶矩方程的解

在研究随机媒质中传播的波的一些有关问题时,常常需要求解波的矩方程。具有不同波数的m-n阶矩方程是一个抛物近似的偏微分波动方程。本文应用格林函数方法将偏微分方程变为积分方程,并用迭代法求得了该积分方程的解。同时,又应用接连散射的方法求解了具有不同波数的m-n阶矩方程,两种方法所得的结果完全相同。文中对解的物理含义作了说明,并讨论了用于波传播研究中的一些问题。     

电离层短波三维射线追踪及其应用研究

从三维射线追踪的Haselgrove方程出发,采用龙格-库塔法求解沿射线路径的电波传播参数,实现了电离层短波数字三维射线追踪,重点对数字三维射线追踪具体实现的一些关键问题处理进行了深入分析研究.本研究工作是结合传播工程技术问题开展的,以一类具体的电离层模型,给出了三维射线追踪在一些传播工程中的具体应用.     

均匀随机媒质中传播的波——有不同波数的m-n阶矩方程的解

在研究随机媒质中传播的波的一些有关问题时,常常需要求解波的矩方程。具有不同波数的m-n阶矩方程是一个抛物近似的偏微分波动方程。本文应用格林函数方法将偏微分方程变为积分方程,并用迭代法求得了该积分方程的解。同时,又应用接连散射的方法求解了具有不同波数的m-n阶矩方程,两种方法所得的结果完全相同。文中对解的物理含义作了说明,并讨论了用于波传播研究中的一些问题。     

基于射线追踪方法的电离层点对点传播问题研究

短波通信和电离层斜向探测本质上都属于点对点传播问题,即固定收发站之间的传播问题,而点对点传播问题的本质是在发射点搜索出合适的仰角和方位角来实现射线的自动导引。射线追踪一直是研究高频波传播现象的工具,基于射线追踪的自导引技术可以实现点对点传播,但不同电离层模型对点对点传播的轨迹和精度会有影响。本文将基于数值射线追踪,利用牛顿自导引技术构建点对点传播模型,研究在分段准抛物(quasi parabolic segments, QPS)电离层模型以及国际参考电离层(International Reference Ionosphere, IRI)模型这两种不同电离层模型下点对点传播算法的稳健性和精确性问题。结果表明,在两种模型下本文算法均有较高的稳健性,但是QPS电离层模型下具有更快的运行速度,而IRI模型下有更高的精确性。     

电离层三维射线追踪的快速计算方法

基于三维射线追踪的Haselgrove方程,实现了快速电离层短波数字的三维射线追踪.根据射线传播的几何关系,给出在电离层以下部分的射线参数计算方法.根据电子浓度梯度的变化和自适应Runge-Kutta法,给出了三维射线追踪中自适应改变积分步长的快速计算方法,并以准抛物电离层模型为例,讨论了利用本文方法与解析解相比的精度,以及与各种不同步长相比的时间和精度.结果表明:采用本文方法在相同精度下速度至少可以提高一个数量级.     

电离层侧向散射传播特性分析

侧向散射探测技术是近几年发展起来的一种新的电离层探测技术.如何基于电离层侧向散射探测结果准确获取探测区域内电离层状态信息,还需要对电离层侧向散射传播特性进行深入分析.本文详细推导了侧向散射来波信号的信噪比方程,并利用三维数字射线追踪技术,仿真得到了不同接收波束指向下的侧向散射扫频电离图,给出了最小时延线、不同地面距离最大可用频率（MUF）等参数的变化规律.     

The wave propagation and mode coupling in warm ionosphere

The wave propagation in warm ionosphere is studied in both homogeneous and inhomogeneous ionosphere. When the temperature of electrons are taken into account, the plasma wave is a propagating wave. The dispersion relation of waves in warm ionosphere has been derived. It is an algebric equation which is analogue to the Appleton-Hartree equation, but in higher order. In a stratified warm ionosphere, the equation forq (Booker’sq) is an algebric equation. Both of these equations are used in study of the wave propagation in the ionosphere by means of ray tracing method. The wave mode linking in homogeneous ionosphere and mode coupling in stratified ionosphere are studied. The mode coupling between plasma wave and electromagnetic wave is discussed through the discussion of singularity of the wave equation. The wave fiold near the wave transformation region can be found out by solving the wave equation near the singularity. The justification of study mode conversion by ray tracing is explained. The results could be useful in the study of wavo absorption process and radio heating experiments in the ionospheres.     

电离层反射区域短波驻波场强的分布研究

精确计算出垂直入射到电离层的HF泵波在整个反射区域的局部电场变化情况对于研究电离层调制实验中产生的各类非线性效应具有十分重要的意义.文章基于泵波垂直入射时一维波动方程和Forsterling方程推导出了特征模式波各电场分量的具体表达式, 并利用“一致近似”的解析法精确计算出线性密度剖面条件下特征模式特征波驻波部分各电场分量和总电场强度在各自反射点附近区域的变化情况.数值计算结果表明:O模式波驻波部分的总电场在其反射点附近区域急剧变化并产生数个极大值, 其幅值增长显著, “电场肿胀”的效应非常明显, 且该效应在高纬地区比在低纬地区更加显著, 地磁场对驻波场强的形态变化具有深远的影响; X模式波驻波部分的电场值在其反射点前虽有一定的增长, 但其增长有限, “电场肿胀”效应远没有O模式波明显.     

Wave Polarization Effects on the Transmission and Reception of lonospheric Radio Waves

The effects of wave polarization on the transmission and reception of ionospheric radio waves have been discussed. Special attention was given to the effects of polarization on the excitation of characteristic waves in the ionosphere, on the absorption losses in the ionosphere, on the reception of arbitrarily polarized plane waves, and on the polarization coupling losses. In this work only one-hop paths were considered and it was assumed that the operating frequency is in the HF region so that ray theory treatment may be applied with high accuracy. The results of investigation have shown that wave polarization is an important and sometimes critical factor in the overall performance of ionospheric radio networks. It is believed that careful consideration of the wave polarization effects in the design of reliable and efficient communication and broadcasting networks can result in relatively lower transmitter power and in the reduction of the number of channels occupied by a particular station.     

Wave packets, group velocities, and rays in lossy media revisited

A study prompted by discussions of the group velocity concept in absorptive media and the correctness of Maxwell's equation is presented. A simple model for a wave packet train is obtained by beating two waves with adjacent frequencies and wavenumbers. By extending frequencies and propagation vectors into the complex domain, it is shown that a consistent definition of real group velocity in absorptive media can be stated. Numerical examples are displayed, and theoretical and experimental aspects are briefly discussed. An extension of Hamilton's ray equations for absorptive media is given. This formalism is used for numerical ray tracing in an absorptive ionosphere. The arguments show that a physically meaningful definition of the group velocity in absorptive media is consistent with the Fermat principle and the special relativistic limitation on the speed of light     

Wave propagation through random media: Contributions from ocean acoustics

Recent theoretical and experimental progress in understanding sound transmission through a random field of internal waves is reviewed. Some attempt is made to place this work in historical relation to similar efforts in radio-wave propagation through the ionosphere and light propagation through the atmosphere. It is emphasized that internal waves as a random medium possess several new features unfamiliar to those dealing with homogeneous isotropic turbulence. The effect of a background deterministic wave-speed variation (the ocean sound channel) is central to the theoretical treatment, which is based on a path-integral solution of the parabolic wave equation. A distinction is made between two sections of the saturated region and some emphasis is placed on the region of partial saturation. Comparison with experiment is discussed with examples from the two-point mutual coherence function of time, frequency, and vertical separation; the intensity correlation in time, frequency, and vertical separation; the spectra of phase and log intensity, pulse propagation, and the higher moments of intensity.     

短波天波反射/地波绕射组合新传播模式及其可能应用

把电离层反射传播模式和地波绕射传播模式组合成新的传播模式.对这一新传播模式的构建形式、新模式的路径损耗因子、频域多普勒谱特性、工作频率特性等传播特性以及它的可能应用进行了研究.以天波/地波集成体制超视距雷达系统作为一种应用,导出了其雷达方程、定位方程和信息处理过程模型.具体的算例表明,该雷达体制有好的可行性.