A Signal-processing Scheme for Passive Acoustical Mapping of Breaking Surface Waves

Abstract

An acoustical system is described with emphasis on its signal-processing scheme. The system consists of a small broadband hydrophone array of span 8.5 m and 5-kHz bandwidth, which is able to track individual breaking surface waves by passive detection of the naturally generated sound of wave breaking. The generalized cross-correlation technique is used to determine time differences of acoustical signals from breaking waves arriving at the array. Breaking events are identified in correlation time sequences, and the identification is aided by image enhancement and pattern recognition. Determination of source positions from the estimated time delays is also discussed. The instrument was first employed during the Surface Wave Program (SWAPP), and preliminary results clearly demonstrate the ability to track individual breaking events. This system can be used to measure some spatial and temporal characteristics of breaking waves, such as frequency of breaking, lifetime, velocity, and spatial distributions.