Theory of HF and VHF Propagation Across the Rough Sea, 2, Application to HF and VHF Propagation Above the Sea

Abstract

This paper deals with an estimation of the effect of sea state on HF and VHF ground‐wave propagation loss across the ocean. For this estimation, an expression is employed that was derived in part 1; it gives the effective surface impedance in terms of the spatial height spectrum of the surface. Two empirical models are employed for the height spectrum of the ocean, the directional Neumann‐Pierson model and the isotropic Phillips wind‐wave model. These effective surface impedances accounting for sea state are then inserted into a standard ESSA computer program giving the basic transmission loss above a spherical earth. The dependence on sea state is plotted in curves which show the excess loss in decibels over a smooth sea. The propagation loss to points at various heights above the sea is also calculated. Normal sea state variations are seen to be negligible below about 2 MHz but produce a maximum excess loss at about 10 to 15 MHz.