Vehicle Motion-Related Noise Mitigation Analyses of a Waveglider Towed Array System for Passive Acoustic Marine Mammal Monitoring

Abstract

With the proliferation of offshore wind construction and the expected impact to marine mammal habitat by pile driving and increased support vessel traffic, passive acoustic marine mammal monitoring has rapidly become a high priority for academic and commercial research interests, as well as government regulatory agencies. Mobile autonomous sensing systems, such as wavegliders have demonstrated efficient, remote, real-time acoustic monitoring with wide-area coverage, particularly when instrumented with towed hydrophone arrays [1]. Arrays have significant advantages over single hydrophone systems due to their capacity for spatial noise rejection and spatial resolution of acoustic sources. Further, when the array is deployed deep below the sea surface through the use of a long tow cable, system noise levels are reduced by isolation from the various vehicle motion-related noise effects. In this paper, we review the design of a waveglider-based monitoring system first introduced in [1], and report on the noise performance of the system with particular emphasis on physical mechanisms that cause the system noise at low frequency. These include flow-induced effects from the waveglider itself, cable strum induced by vortex shedding from the tow cable, residual vertical motion at the sensor induced by surge and vortex shedding, and turbulent boundary layer flow noise over the moving hydrophone array.