Improved estimates of HF radiowave field strength near a land-sea interface

Results of other researchers are extended to give the detailed behavior of mixed-path (land-sea or sea-land) propagation near the land-sea interface. It is shown that the mechanism for groundwave-mode coupling at the land-sea interface is edge-diffraction, and that near the shoreline the direct edge-diffracted wave can make a significant contribution to the field. It is further argued that, for sea-to-land propagation for an elevated observer, the sea-type groundwave modes extend over land, and there is a shadow zone for the land-type groundwave modes excited at the shoreline. Corresponding results hold for land-to-sea propagation.