计算电离层VLF波传输特性的时域有限差分算法

摘要

在星载甚低频( VLF)通信技术中，研究甚低频信号在电离层中的传输特性具有重要意义。现有的利用时域有限差分( FDTD)算法研究电离层传输特性大多基于高频脉冲信号，且传播模型相对粗略，计算存在一定误差。为此，建立了更为精确的电离层各向异性传播模型，对常规的FDTD算法引入变步长因子，并用该算法对VLF波在电离层中的场强衰减进行了数值计算，研究了昼夜变化及频率对其传输特性的影响。仿真结果与卫星实测数据对比表明：与常规的FDTD算法以及全波分析方法相比，引入变步长因子的FDTD算法精度更高；在VLF频段，降低频率有利于电磁波穿透电离层，且白天的衰减明显大于夜间；VLF波在射入电离层并穿透D层时衰减严重(30~40 dB)，约为F1层中衰减的3倍。%Research on very low frequency( VLF) signal transmission characteristics in the ionosphere is vi-tal for satellite VLF communications. Existing finite difference time domain ( FDTD ) algorithms on the study of ionospheric propagation properties are mostly based on high-frequency pulse signal and propaga-tion model is relatively coarse,and there is a certain calculation error. Therefore,a more precise anisotropic ionospheric propagation model is established, and variable step size factor is introduced to conventional FDTD method . With the algorithm, VLF wave field in the ionosphere strong attenuation is calculated to study the frequency changes and effect on the transmission characteristics of day and night. Comparison be-tween simulation results and satellite data shows that compared with the conventional FDTD algorithm and full-wave analysis method,FDTD method introducing variable step factor has a higher calculation accura-cy;at VLF band,reducing the frequency is helpful for electromagnetic waves to penetrate the ionosphere and the attenuation during the day is significantly greater than that at night;VLF waves attenuate greatly in entering the ionosphere and penetrating the D layer (30~40 dB) ,which is about 3 times in F1 layer.