Multibeam sonar water column data simulation for improved and automated detection of gas seeps

Abstract

Water column data (WCD) collected by multibeam echosounders (MBES) provide valuable datasets for the detection of gas bubbles. However, the presence of noise patterns, primarily caused by sidelobe interference from seafloor reverberation, limits the usability of WCD. We present a method for simulating characteristic noise patterns in WCD, particularly in Mills Cross configurations, by simulating predicted seafloor reverberation and transducer artefacts. The simulation is based on a reference pattern created from a subset of data and then applied as a correction based on the depth and seafloor backscatter of each ping within the dataset. Noise patterns can be removed by subtracting the simulated data from the original data, allowing for improved analysis of near-benthic water column features such as gas seeps. This method requires no prior knowledge of specific transducer characteristics, making it applicable to a wide range of MBES systems and acoustic targets. This method was applied to two MBES datasets collected simultaneously over a seep field in the Bay of Plenty, New Zealand, as part of the Quantitative Ocean-Column Imaging (QUOI) voyage in July 2018. We demonstrate the utility of applying a reference pattern for detecting the spatial extent of gas seep bases mapped using two different frequencies.