Estimating ocean wave directional spectra from measurements of water particle motion by a surface buoy acoustic ranging system

Abstract

An instrumentation design is presented for estimating ocean wave directional spectra from measurements of water particle motion. For relatively shallow water and short term measurement applications, it is shown to be an effective and reasonably accurate system for estimating ocean wave directional spectra. Specifically, water particle motion is measured using an underwater, acoustic, ranging system consisting of a surface projector buoy and suitable bottom mounted hydrophones. A continuous wave signal is emitted by the surface projector buoy and the resultant signal delays at each hydrophone provide slant range information for triangulating the buoy position. Signals from the buoy and hydrophones are recorded for later processing and analysis. A method for estimating wave amplitude, phase, and direction is also presented. Wave data obtained from a commercial bottom mounted pressure gauge serve as a reference for comparing water particle displacement measurements recorded by the instrumentation system. Similarly, aerial photographs taken of the wave field in the study area during the experiment were used as a reference for comparing wave directions.