UACE2017 Proceedings: Evaluating the performance of a coherent array in a high-flow tidal channel

• Session:
  Acoustics of marine renewable energy developments
• Paper:
  Evaluating the performance of a coherent array in a high-flow tidal channel
• Author(s):
  Matthew Auvinen, David Barclay
• Abstract:
  Baseline ambient sound level assessment is important in quantifying the potential impacts of additional noise contributions from tidal energy infrastructure on the marine habitat. Static acoustic sensing in high-flow conditions is complicated by flow-noise, or pseudo-sound, generated by low frequency pressure fluctuations due to turbulent flow over the surface of a hydrophone. In October 2016, a four-element horizontal hydrophone array was deployed in the Minas Passage in the Bay of Fundy during a period from maximum ebb to slack tide. Minas Passage experiences turbulent flow with mean speeds greater than 2 m/s and a tidal range greater than 13 meters and is the site of an in-stream tidal energy test facility. Observations of spectral slope and horizontal spatial coherence are used to track the masking effect of turbulence across frequency and flow speed. The array's performance is quantified by an empirical relationship between current speed and the critical frequency, defined as the frequency at which flow-noise ceases to mask the true ambient noise. Coherent processing (beamforming) is applied and shown to improve the performance of the array by exploiting the incoherent nature of the flow-noise. Array measurements were compared against simultaneous co-located single hydrophone Lagrangian (drifting) measurements. The baseline ambient noise field is assessed and a quantitative prediction of low frequency performance of an array with an arbitrary number of elements is proposed.
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Contact details

• Contact person:
  Dr David Barclay
• e-mail:
  
• Affiliation:
  Dalhousie University, Department of Oceanography
• Country:
  Canada