Ambient Noise Measurement in Turbulent Tidal Flows

The OBJECTIVES of the proposed research are: (1) to implement flow-noise reduction measures to enableambient noise measurements to be made in high-speed tidal flows; (2) to quantify the efficacy of thesemeasures using Canadian-built digital hydrophones in a Nova Scotia tidal channel targeted for tidal powerdevelopment; (3) to obtain measurements over a one-month period of natural ambient noise conditions,including marine mammal sounds, prior to the deployment of a test turbine in this channel.The APPROACH will involve a combination of physical shrouds on the hydrophone transducers, andcoherent processing of the signals from paired hydrophones to reduce contamination from flow noise, themajor impediment to routine monitoring of ambient noise in high-speed tidal flows. A single shroudedhydrophone will be used for the high O(100 kHz) frequencies (of some marine mammal echo-location clicks),at which the pressure fluctuations due to turbulence in the boundary layer are much reduced. The synchronizedhydrophone pair will be used for the lower frequency measurements, utilizing the shorter spatial decorrelationscales of turbulence fluctuations to separate marine mammal sounds from flow noise. A bottom-mountedacoustic Doppler current profiler and single-point Acoustic Doppler Velocimeter will be deployed in theimmediate vicinity of the hydrophone to measure the tidal current profile and nearbed turbulence.The SIGNIFICANCE of the project is its direct relation to the planned development of in-stream tidal powerin the Minas Basin and other tidal passages in the Bay of Fundy. These developments, if successful, represent asignificant source of renewable electrical energy for the province of Nova Scotia and, by extension, other highflow tidal passages on Canada's Pacific Coast and in the North. An important gap exists world-wide in thetechnology available for ambient noise measurement in high-speed tidal flows, and thus for determiningturbine noise levels, how this sound might be related to turbine performance, and how to use sound to monitormarine mammal/turbine interactions. The proposed research directly addresses this technological gap.