Measuring the sound of bubbles: Passive acoustic gas flux inversion

There is an ever growing need to be able to detect and quantify marine gas seeps, both natural and man-made. One potential avenue for achieving this is via passive acoustic flux inversion. Such techniques use the frequency of oscillation of newly released bubbles (the Minnaert frequency) to determine the size (radius) and number of bubbles released from a seep in a given time. Passive acoustic flux inversion offers a number of advantages over active acoustics, namely, being low cost and energy making them ideal for long term monitoring of known sites. Recent studies have demonstrated how passive acoustic inversion can provided fresh insight into the variability of natural seeps, with changes being correlated to tides, surface seiches, and even day/night temperature cycles. Furthermore, we are now applying this technique to monitor volcanic activity, correlating changing rates of gas release with increasing volcanic activity, developing a new eruption monitoring tool. This talk will introduce the theory behind passive acoustic gas flux inversion, detail case studies and future projects with an open invitation for collaboration.