Active acoustic measurement of sound speed for quantifying underwater gaseous bubble emissions

Abstract

Artificial or natural processes can cause underwater gas leakage, which often forms upwelling bubbly plume. The interaction of gaseous plume with acoustic waves would result in the variation of sound speed, which makes it possible to monitor the upwelling process via active acoustics. In this work, we build a numerical model to simulate the transport of gaseous bubbles and the sound speed response to the plume in the acoustic channel. The effectiveness of the model is validated by conducting a tank-based experiment, in which the sound speed variations were measured by varying gas flow rates. Meanwhile, signals at six frequencies (1 to 8 kHz) were transmitted and propagated through the medium part of which was occupied by the gaseous plume. Moreover, the comparison results also give a matched bubble size distribution (BSD), which further confirms the validity of the proposed model.