Modeling mid-to-high frequency acoustic signal fluctuations induced by fetch limited sea surface roughness in shallow water

Abstract

Surface waves are among several environmental parameters that significantly influence mid-to-high frequency (1–18 kHz) acoustic wave propagation. In coastal regions, surface waves are fetch limited with reduced spectral level at lower frequencies. In order to assess the detail of an acoustic signal interaction with the sea surface in such regions, a combined approach based on experimental observation and modeling of both surface waves and acoustic waves has been adopted. Data from two broadband shallow water acoustic experiments are presented. These data include simultaneous wind speed and acoustic propagation measurements. The experimental design allowed an examination of received signals corresponding to single surface bounced ray paths. Measured data analysis shows a high correlation between time–angle–intensity fluctuations of received signals and varying sea surface conditions. An empirical fetch-limited ocean wave spectrum has been combined with an acoustic ray-based model to study acoustic wave propagation. Rough sea surface realizations are generated and used as sea surface boundaries with the acoustic model. This combined sea surface/acoustic model predicts the variability of acoustic signal fluctuations as a function of varying sea surface. Modeled time–angle–intensity signal fluctuations compare excellently with field data at lower wind speeds.