Multiple-Path Interference and Phase Standard Deviation of ELF Radio Wave Propagation in an Anisotropic Earth-Ionosphere Waveguide

In this article, the multiple-path interference (MPI) and the phase standard deviation of extremely low frequency (ELF: below 30 Hz) waves propagation in an anisotropic Earth-ionosphere waveguide is investigated. The theoretical analysis of the phenomenon of MPI and the phase standard deviation for ELF wave propagation in an anisotropic Earth-ionosphere waveguide are first given. Calculations demonstrate that MPI becomes significantly apparent when the propagation distance exceeds one wavelength. Furthermore, the electric field amplitude calculated in the anisotropic case matches better with the measured data compared to the isotropic case. Due to the influence of the geomagnetic field, noticeable directional differences are observed in the distribution of phase standard deviation. It is also found that the locations of maximum phase standard deviations of the electric field amplitude coincide with the locations of minimum electric field amplitude. Additionally, there is a noticeable aggregation of the interference at certain heights and the intensity at nighttime is greater than that during the daytime.