Propagation of LF ground-wave through inhomogeneous atmosphere

Atmosphere refractivity is one of the most important parameters in the low frequency (LF) ground-wave propagation. It is predominantly horizontally stratified and time dependent. In this paper, the 2-D rotational symmetric moving window finite-difference time-domain algorithm is employed to investigate the impacts of different refractivity-height profiles on the field strength and time-delay of the LF ground-wave propagation through inhomogeneous atmosphere. The impacts of the refractivity's seasonal and diurnal variations are also studied. Taking Loran-C system as an example, numerical results show that the refractivity-height profile has relatively large impact on the time delay. Using a linear height profile can lead to an error on the time delay at the level of hundreds of nanoseconds with a propagation distance of 1000 km; while for the same propagation distance, the refractivity's seasonal and diurnal variations may affect the time-delay on the order of several tens of nanoseconds.