Abstract:

While the sound of breaking deep-water waves has received considerable attention since being identified as the dominant source of wind-driven noise in the open ocean five decades ago by Knudsen, there have been relatively few acoustic measurements of breaking surf. Here measurements of the acoustic signature of breaking surf in the very near shore region are presented. A two-hydrophone acoustic system was deployed approximately 100 m from the shoreline to measure the broadband coherence of single breaking waves. The horizontal directivity of the breaking wave noise can be inverted from measurements of the noise coherence. These inversions reveal the presence of acoustic ``hot-spots'' which follow the break-point of a wave as it moves along the beach. An interpretation of the acoustic hot-spots in terms of a wave's moving break-point and bubble plume formation will be given. [Work supported by ONR as part of the Adaptive Beach Monitoring experiment.]