Influence of fetch limited surface roughness on mid-to-high frequency acoustic propagation in shallow water

Abstract

Surface waves are among several environmental parameters that can influence broadband mid-to-high frequency (1–18 kHz) acoustic wave propagation. Understanding the interaction of sound waves at a rough surface requires a detailed description of the ocean wave spectrum. In shallow water regions, due to proximity to land, surface waves are usually fetch and duration limited with reduced spectral level and higher frequency components. A model that approximates the wave spectra for a fetch limited sea has been combined with acoustic ray-based method for analysis of forward scattered acoustic signals in such a coastal environment. Numerical modeling is employed to investigate time-frequency-angle characteristics of ray paths reflected from a rough sea surface. Temporal variability of acoustic signal fluctuations has been examined as a function of varying sea surface. To validate this model, results are compared against a unique set of experimental data collected in a fetch limited region. The experimental design allowed an examination of time evolution of a single surface bounced ray path. Simultaneous wind speed and acoustic propagation measurements allowed correlation between the individual ray paths and the sea surface at varying sea state conditions. For low wind speed conditions, model results predict the temporal fluctuations of the measured acoustic signal propagation.