Estimation of methane bubbles volumetric flows from acoustic data of water column
Résumé
Since few years, advances in technology and computer processing of devices initially designed for seafloor mapping allow to carry out acoustic surveys of the entire water column. These are revealing that gassy sediments and free gas emissions from the seafloor are much more frequent than expected which call for new experiments to characterize these plumes. Beside the primary scientific need to position the gas emission in the bathymetry of the area, quantification of bubbles volumetric flows is one of the important scientific issue to solve. The work proposed here explore the feasibility of assessing the volume of bubbles plumes and their temporal variations from acoustic data with a methodology similar to that used in acoustic fisheries, i.e. by inverse modeling of the acoustic backscattered data. Sounder used in these experiments is a split-beam fisheries sounder at 120 kHz installed on an autonomous module named BOB (Bubble OBservation Module). Experiments in sea water tank were done to have a validation of the inverse modeling on controlled bubbles flows, the method was then applied to in situ natural gas seeping from the seafloor obtained during a survey in Marmara Sea in 2009.