Observations of underwater sound from laboratory breaking waves and the implications concerning ambient noise in the ocean

The results of an experiment to characterize the underwater sound field radiated by various breaking waves intensities in fresh water in the range from 0.1 to 20 kHz are described. Waves are generated by a computer‐controlled plunging‐type wave maker and propagate along a 12.7‐m‐long channel where they are made to break at the mid‐surface of a 3‐×3‐×2.5‐m anechoic water tank. The individual bubbles and bubble clouds entrained by the breaking wave provide a mechanism for sound production. Using high‐speed cinephotography, correlations were established between the hydrodynamic evolution of the cloud and the radiated acoustic emissions. The bubble size distributions inside the cloud were measured with the aid of a high‐speed video camera and a fiber optic cable. These measurements indicate that single bubbles with radii as large as 7–8 mm may be entrained in this fresh‐water system by moderate spilling breakers. Detailed measurements of the bubble size distribution of the bubble cloud enabled us also to obta...