Abstract:
Experiments have been conducted to investigate sound propagation through two types of bubble layers. The first is a motor boat wake, and the second is the near-surface ocean bubble layer beneath breaking waves. The bubble distribution over depth in both cases produces an upward-refracting sound-speed profile which acts as an acoustic waveguide. The motor boat wake is very stable and provides a controlled environment in which to study waveguide propagation, and, in contrast, the ocean surface bubble layer which is naturally generated by the injection of bubbles from breaking waves is much more variable. A broadband source was used to insonify the wake layer, while the bubbles formed by breaking waves were the acoustic source in the naturally generated ocean bubble layer. Inverse-square theory will be used to interpret spectra from both experiments, and comparisons will be drawn between the spectra seen for the stable wake experiment and the variable ocean bubble layer. [Work supported by ONR.]