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Passive Acoustic Monitoring for Tidal Energy Projects

Brian Polagye, Chris Bassett, and Jim ThomsonUniversity of Washington

Northwest National Marine Renewable Energy Center

Ecological and Environmental MonitoringApril 7, 2011

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Evaluating Acoustic EffectsMarine Mammal Behavioral

Response to Sound

Sound Received by Marine Mammal

Individual Life HistoryContext for Received Sound

Sound generated by turbine

Site-specific sound propagation

Marine mammal hearing sensitivity

Ambient noise from other sources

Marine mammal activity state

Exposure to similar sounds

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Quantifying Sound from Turbines

Common spectral peaks

(100 Hz – 3 kHz)

AHD at fish farm

Bedload transport

Nearby shipping

Data collected by Scottish Association of Marine Sciences

OpenHydro turbine (6 m diameter)

Drifting EARs data collection

Compare drift series to identify turbine-specific features

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Marine Mammal Hearing Sensitivity

Southall et al. (2007) Marine mammal exposure criteria

fRfR

fMmax

log20 10

2222

22

lowhigh

high

ffff

fffR

Turbine Noise

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Implication for Received Levels

Broadband Levels Mid-frequency Cetaceans

4x reduction in area ensonified to 120 dB

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Stationary Hydrophone MeasurementsLoggerhead DSG

Autonomous hydrophone (32 GB capacity)

80 kHz sampling 2% duty cycle for 3 months

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Temporal and Spatial Variability

Cumulative Probability Density

Hydrophone Deployments

Temporal variability dominates over spatial variability

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Vessel Traffic Monitoring with AIS

Automatic Identification System (AIS) transponders required on all vessels greater than 300 tonnes gross weight and passenger vessels

Continuous data collection and archiving

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Data Assimilation

SPL

(dB

re 1

μPa

)Distance to closest vessel (km)

Vessel Proximity Noise Correlation

Vessel noise drives broadband noise levels

Source: Chris Bassett, forthcoming PhD dissertation

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Implication for Evaluating Noise Effects

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Sound during High Currents

Hydrophone Response

Current Velocity

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Flow Shield Experiment

Hydrophonewith Flow Shield

Unshielded Hydrophone

Doppler VelocimeterSample volume aligned with

hydrophone element

High Velocity Region

Quiescent Region

High Porosity Foam

Hydrophone Element

Hydrophone Pressure Case

Source: Chris Bassett, forthcoming PhD dissertation

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Pseudo-Sound Identification

Unshielded Hydrophone

Hydrophone with

Flow Shield

Source: Chris Bassett, forthcoming PhD dissertation

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Propagating Sound during High Currents Bedload transport

― Elevated noise at 5-50 kHz

― Consistent with size of gravel and shell hash observed during ROV surveys; O(1 cm)

Turbulent flow over rough surfaces― Potential contribution from advected turbulence

― Cannot measure velocity fluctuations directly at frequencies of interest (e.g., > 300 Hz)

88.0

209

Df (Hz) (Thorne, 1986)

Source: Chris Bassett, forthcoming PhD dissertation

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Measuring Noise from Tidal Turbines

Parameter Stationary Hydrophone

Drifting Hydrophone

Pseudo-Noise Filtering Physical shield Inherent filtering

Measurement Duration Months Hours

Deployment Depth Seabed or Turbine frame

Variable (easiest near surface)

Spatial Resolution Low High

Temporal Resolution High Low

Long-term, low-intensity monitoring

Short-term, spatial characterization

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Thank You

This material is based upon work supported by the Department of Energy and

Snohomish County PUD under Award Number DE-0002654.

Joe Talbert for keeping all equipment in working order.

Sam Gooch, Joe Graber, and Alex DeKlerk for helping turn around instrumentation.

Captains Andy Reay-Ellers for piloting skills during instrumentation deployment.