Observation of high‐frequency ambient noise generated by capillary waves

Abstract

In the absence of breaking gravity waves, capillary waves may contribute to the generation of ambient noise in the ocean. Surface profiles of capillary water waves, with surface tension as a restoring force, are picked 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 wavelength, respectively) the free surface in the trough folds onto itself, encapsulating an air bubble. By blowing air over a water‐filled, Plexiglas tank, 6bubble‐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 videotape. The initial findings of an experimental study of generation, size distribution, and acoustic emissions of bubbles produced by capillary water waves are presented. [Work supported by ONR.]