A Preliminary Experiment on the Detection of Bubbles in the Sea with Side-Scan Sonar

Abstract

Detection of CO2 bubbles in the water column is a candidate for detecting CO2 leakage in the marine monitoring at offshore CO2 storage. To investigate ability of side-scan sonar (SSS) to detect bubble plumes, experiments were conducted where air bubbles released at the seabed were observed with SSS. Combining the release rate (20 ml/min, 100 ml/min, or 200 ml/min), the size of bubbles (a diameter of 1 cm or tiny), the cruising speed (2 or 3-4 knots; 1 knot = 1.852 km/hour), and the observation line (near or off the release points), we tested 28 cases. A tiny bubble plume was much easier to detect with SSS than a 1 cm bubble plume, and the detection limit of the release rate was estimated to be not larger than 20 ml/min for a tiny bubble plume, and not smaller than 20 ml/min for a 1 cm bubble plume, under the present experimental conditions. Estimation of the release point with SSS and application of SSS to detection of CO2 bubble plumes were discussed, and it is conjectured that SSS could detect CO2 bubbles at a practical level.