Development of a low-frequency high-flow acoustic sensing array for turbulent ocean conditions

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In order to quantify the potential environmental impacts of tidal turbine installations effective broadband acoustic sensing is required to perform passive acoustic monitoring (PAM) of marine life, as well as measurements of noise produced by the turbines and associated infrastructure. However, in tidal channels, high turbulent flow causes pseudo-noise (flow noise) to be generated on the surface of the acoustic sensors, which is especially problematic at lower frequencies where it masks the true sound field. The use of multiple synchronized hydrophones along with array signal processing techniques is a proposed solution to this challenge, allowing uncorrelated pseudo-noise to be suppressed while sounds generated by marine mammals, natural ambient sources, and anthropogenic sources may be enhanced, separated, and classified. A horizontal line array will be designed and deployed on a tidal turbine currently in use at the Fundy Ocean Research Center for Energy (FORCE) site. The effectiveness of the array in minimizing flow noise while accurately measuring ambient noise, marine mammal sounds, and turbine-generated noise will be evaluated. The collected data will be compared against a benchmark data set collected on a single free-drifting hydrophone using parabolic equation and ray tracing acoustic models to account for propagation effects. These models will also be used to evaluate the effectiveness of turbine noise monitoring in the near field versus the far field. Performance parameters as a function of the number of array elements, element spacing, and flow speeds will be quantified. The results of the study will verify and validate the effectiveness of acoustic arrays for long-term PAM in environments where high-speed turbulent flow would otherwise mask measurements with pseudo-noise.