Propagation of radio waves past a coast line with a gradual change of surface impedance

The amplitude and phase of a radio ground wave are calculated for an oblique crossing of a flat-lying coast line. The surface impedance is allowed to change in a continuous and gradual manner in the vicinity of the coast line. The earlier results for an abrupt boundary are recovered as the width of the transition zone is reduced to zero. In general, it is found that the presence of the transition region will not produce a significant modification of the transmitted field. On the other hand, the reflected waves and the behavior of the field near the coast line are profoundly influenced by the width of the transition. In particular, certain singular behavior of the field associated with an abrupt boundary is virtually eliminated when the transition zone has a finite width.