On mode conversion of VLF radio waves at a land-sea boundary

Propagation in the earth-ionosphere waveguide is considered for the situation where the earth's boundary has an abrupt change in the surface impedance. The formulation, which utilizes medal analysis, includes the effect of the usually ignored reflected modes. It is demonstrated, however, that these may be neglected in most practical situations even when the surface impedance contrast is large. The relationship with an earlier integral equation approach to the problem is pointed out.