The production of high-frequency ambient noise by capillary waves

The quantitative characterization of noise sources in the ocean is a task which has attracted growing attention in recent years. In the absence of breaking gravity waves, capillary waves may contribute to the generation of high-frequency ambient noise. Surface profiles of capillary water waves are peaked downward in the troughs and relatively flat at the crests. At a limiting amplitude given by H/λ= 0.73 (where H and λ are the wave height and wavelenght, respectively) the free surface in the trough may fold onto itself, encapsulating an air bubble. By blowing air over a water-filled, plexiglass tank, bubble-producing capillary waves can be generated in the laboratory. Underwater acoustic emissions from these bubbles were monitored and a visual record of their formation was established via a high-speed video tape. The initial findings of an experimental study of the generation, size distribtuion, and acoustic emissions of bubbles produced by capillary water waves is presented.