Influence of Irregular Terrain on LF One-Hop Sky-Wave Propagation Delay in the Presence of Natural Magnetic Field

Studying the impact of terrain undulation on low-frequency (LF) sky-wave propagation delay is of great significance for exploring the potential applications in low-ionospheric detection, remote navigation, and timing service. This letter combines gradient ionospheric parameters and uses the finite-difference time-domain method to calculate the reflected signal of LF radio waves from the ionosphere. Using the sky- and ground-wave separation technologies in time domain, the variation law of LF sky-wave propagation delay with terrain changes is given in both daytime and nighttime models. At the same time, this letter also analyzes the influence of different ionospheres (in the presence or absence of natural magnetic field) on LF one-hop sky-wave propagation delay, providing some reference significance for studying the propagation characteristics of LF sky waves.