Acoustic Focusing in Shallow Water and Bubble Radiation Effects

摘要

The long-term goals of the 'Acoustic Focusing in Shallow Water and Bubble Radiation Effects' project is as follows: (1) understand the role of wave-induced bubbles in the upper ocean boundary layer on the performance of underwater communications systems and ambient noise generation, (2) study the implications of focusing by surface gravity waves on Doppler sonar and acoustic communications systems in shallow and very shallow water, and (3) study the performance of acoustic vector sensors in very shallow water. Goal 1 of this research is to measure the radiation strength of fragmenting bubbles as a function of bubble size. This research is based on the importance of ambient noise in the ocean for the operation of acoustic systems in general, and the importance of upper ocean boundary layer bubbles on the performance of underwater acoustic systems. The connection between the noise radiated by white caps and wind speed is well known, but the connection between bubble creation mechanics within white caps and noise level is not well understood. Recent advances in our understanding of the scale dependence of bubble creation mechanisms in breaking waves has raised the possibility of creating a quantitative link between ambient noise level and bubble production rates by ocean waves. Goal 2 is to measure and model the three-dimensional effects of sound focusing by shoaling surf. Wave crests focus surface reflections into high-intensity regions that propagate through the water column. These high intensity regions have a first-order impact on the performance of underwater communications systems in the surf zone. Goal 3 determines how closely the performance of an array of vector sensors deployed in an ocean environment approaches theoretical prediction; compares the performance of vector sensors with pressure sensors; and determines if any differences in performance can be related to the relevant physical properties of the water column, such as internal wave activity.