Advanced Detection of Underwater Gas Seep Sites Through Multibeam Echosounder Water Column Data and Numerical Analysis

Abstract Water column imaging of multibeam echosounder systems (MBES) are sensitive and potential devices for investigating free gas bubbles release and their ascent up the water column. These data could demonstrate previously undetected characteristics on the water’s surface and seabed which are related to Sustainable Development Goal 14 about life below water. The research utilizes a MBES to map the volume of seabed gas emission bubbles in the Adriatic Sea, Italy, using water column data. The survey covered 1.5 km 2 around a four-legged gas platform at a depth of 77 meters. To achieve a 50% overlap, ten parallel transects of 1.5 km each were used, with a vessel speed range of 2-2.6 m/s and a transect spacing of 100 m. Acoustic waves from seabed seepage were visualized using water column data, with reflection intensities ranging from −63.5 dB to 29 dB, reflecting the acoustic reflectance of various suspended materials. More precise thresholds were obtained by filtering and clustering the gas bubbles using the point weight approach to separate them from the noise and water bubbles. The uneven Digital Terrain Model (DTM) indicates gas emissions through water column data. The volume of gas bubbles was determined by visualizing the points in a 3D format using XYZ coordinates. Through interpolation techniques and 3D volumetric analysis, six bubble locations were obtained with volumes of 651.12 m 3 , 108.30 m 3 , 42.00 m 3 , 167.20 m 3 , 186.00 m 3 , 287.81 m 3 , and 45.00 m 3 . This study is crucial because it questions the methods of Carbon Capture and Storage (CCS) by investigating the discharge of carbon into the sea. Furthermore, this study helps to identify emission sources, measure the volume of released gas, and explain the depth distribution of emissions, providing essential data for marine CCS assessment.