Improving seep detection by swath sonars with adaptive beamforming

Abstract

Detection of gas seeps is currently of interest for a wide variety of applications. The oil and gas industry can use it to monitor their installations, e.g. oil wells and pipelines. It may also contribute to the understanding of geological and biological activity in the seabed. In a climate perspective, it is also important for estimating the amount of methane that seeps into the atmosphere and monitoring CO2 stored in geological structures. Seeps are commonly detected by bathymetric swath sonars. Bubbles are strong acoustical targets and may form clear flares in the water column display, depending on the size and density of the bubbles. Detection is often easy before the first bottom return arrive and is gradually masked by the seafloor reverberation at longer ranges. We propose to use the sidelobe suppressing properties of adaptive beamforming to suppress seafloor reverberation and extend seep detection range. To investigate this in practice we placed an artificial seep at approximately 45 m depth and mapped it with a swath sonar. We ran lines over the seep at between 0 and 80 m horizontal range. Our processing chain allows us to process each ping with both standard and adaptive beamforming, providing easily comparable results.