Application of Low-Frequency Acoustic Signals to Study Underwater Gas Seepage

Abstract

Remote sensing of seeps, the release of gas (mainly methane) from the seabed, is an urgent problem. The importance of detecting seeps in the Arctic shelf zone is constantly increasing due to degradation of underwater permafrost and the release of gas hydrates. Gas bubbles scatter underwater sound and their corresponding resonance frequencies are in the kilohertz range for seeps observed in nature. A promising method for detecting and studying seeps is probing with underwater sound near the denoted resonance frequency. This corresponds to a decrease in the operating frequency with respect to the traditional method of studying high-frequency sonars, so the proposed method will be classified as low-frequency in this study. This method expands the study area due to the low sound attenuation in water and the high scattering level near bubble resonances. The scattering strength was estimated taking into account collective interaction (group effects) of bubbles. The possibility of using low-frequency hydroacoustic systems to detect seeps is demonstrated using the results of a full-scale experiment using a simulated bubble jet as an example. A data processing method for detecting nonstationary scatterers is proposed.