Characteristics of the low- and high-frequency ambient sound from breaking waves in the surf zone

An experiment was conducted along the Scripps Institution of Oceanography Pier to study the characteristics of the ambient sound in the surf zone. The role of the single large bubble’s (order of a few centimeters) oscillations versus the collective oscillations of bubble clouds as possible mechanisms of generation of the low-frequency sound, especially the relatively broadband peak that appears around 20 Hz in the sound spectrum, is discussed. The frequency band at which ambient sound from breakers in the surf leaks out is identified. The acoustic attenuation which makes the surf zone extremely quiet above 2 kHz, and a possible method to use ambient sound to infer bubble size distribution in shallow water near the surf zone, are discussed. [Work supported by ONR.]