Time statistics of propagation over the ocean surface: A numerical study

Temporal evolution of the ocean surface affects the received signal characteristics in a shipboard communication system. Predicting these time-varying properties is important in studying multipath fading problems. A statistical channel description to the second order is provided by knowledge of the coherent and incoherent power levels as well as the power spectrum of the received field. Several other time-dependent properties of a Gaussian channel can be determined from these statistics. In this paper, a method of moments (MoM) model for propagation over a one-dimensional (1-D) time-evolving, perfectly conducting rough surface is applied to numerically study time statistics of propagation over the ocean. The ocean surface is described by a Pierson-Moskowitz spectrum and evolves in time according to a linear hydrodynamic dispersion relation. Due to the large size of propagation geometries in terms of the electromagnetic wavelength, an efficient numerical method is required to complete the simulation in a reasonable time. The recently developed forward-backward method with a novel spectral acceleration (F-B/NSA) technique is applied and enables time-evolving simulations for many realizations to be calculated so that reasonable statistics are obtained. Numerically obtained results for the coherent and the incoherent powers are illustrated. These results are compared with available analytical approximations to investigate the success of the approximate methods. Particular emphasis is placed on comparison with the Kirchhoff approximation, which provides reasonable predictions for smoother surface profiles and larger grazing angles.