Recent analytical investigations of electromagnetic ground wave propagation over inhomogeneous earth models

A consolidated review is presented of recent analytical studies of electromagnetic waves propagating over inhomogeneous surfaces. Emphasis is on smooth boundaries that can be characterized by a local surface impedance. A general integral equation formulation is developed for this situation. A number of special cases are then considered and various methods of solution are described. Various concrete examples are presented, particular with regard to effects that occur at coastlines. Extensions to certain types of terrain features are also treated using the closely related mode-matching method. Some controversial aspects of very recent work on the subject are descried briefly.