甚低频在多模干涉区的场强起伏标准偏差估计

Estimation of VLF amplitude standard deviation in multimode interference region

对于甚低频(VLF)电波而言,电离层随机不规则变化将影响传播路径上场强的稳定性,从而使得场强起伏在多模区特别是场强极小点附近较为明显。从VLF电波传播基理出发、研究分析了传播路径上电离层随机不规则变化对场强稳定性的影响,推导了多模干涉区、单模干涉区及场强极小点附近激励因子、哀减率和相速与场强起伏的关系,得出了传播路径上场强起伏标准偏差估计公式,并将此公式的理论计算结果与实测数据进行了对比。结果证明:此公式计算精度较高,能够自适应于多模干涉区、单模干涉区,此场强起伏标准偏差估计公式对VLF通信可靠性的研究具有重要意义。

The ionospheric random irregular variety induces the amplitude fluctuation of very low frequency（VLF） wave, which is acute in the multimode interference region especially near the points where VLF field strength is minimum. Base on the standard deviation of the ionospheric reflect height, the fluctuation of attenuation rate and phase velocity for each mode are estimated with the theory of VLF wave propagation, then an estimation formulation of standard deviation for total filed is deduced. This formulation may be used both in the multi-mode and unimode regions, the calculation result of the formulation coincides well with the experiment datum. The formulation of standard deviation of amplitude fluctuation benefits the study about dependability of communications using VLF wave.