Dynamic behaviour of sound generated by gas bubbles injected underwater

The sound generated by vibrating air bubbles injected into water allows for passive detection of targets such as divers and gas leaking from underwater pipes. In this paper, the decaying sound generated by a single bubble is described, and this result is applied to a continuous train of identical bubbles generated by a single nozzle. The resulting acoustic pressure signal after a short transient time has a periodic waveform. The spectrum of this waveform has several harmonics with a fundamental frequency close to the peak of the single bubble spectrum. This signal can be extracted from the ambient noise by a suitable comb filter. These results can be extended to a plume of bubbles generated by an array of nozzles. It is shown that these bubbles can generate an acoustic signal that can be used for passive remote sensing.