NNMREC

April 20, 2011

Ambient Noise in Admiralty Inlet

Chris Bassett, Brian Polagye, and Jim ThomsonUniversity of Washington

Northwest National Marine Renewable Energy Center

NNMREC PI Update

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Recording HydrophoneLoggerhead DSG

Parameter Value

Sample Rate 80 kHz

Storage 32 GB (Flash)

Effective Sensitivity

-165 dB re 1V/μPa

Linear Response 20 Hz – 40 kHz

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Ambient Noise SourcesBedload TransportShip

AverageConditions Quiet

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Ambient Noise CharacteristicsCumulative Probability

DensityHydrophone Deployments

Temporal variability dominates over spatial variability

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Strong CurrentsOvernight Lull in Shipping

First Run for Passenger Ferry

Recording Hydrophone

Automatic Identification System

DopplerProfiler

Establishing Context for Observations

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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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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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Ambient Noise Summary

Ambient noise levels in Admiralty Inlet are high― Mean broadband SPL ≈ 119 dB re 1 μPa (20 Hz – 30 kHz)― Ambient noise exceeds NMFS marine mammal harassment

threshold ≈50% of the time

Sound from shipping dominates ambient noise― Will complicate turbine noise measurements

Measurements during strong currents are challenging― Flow shields can significantly mitigate contamination by

pseudo-sound― Bedload transport likely contributes to high current noise

budget

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Thank YouThis material is based upon work supported by

the Department of Energy and Snohomish County PUD under Award Number DE-0002654 and the National Science Foundation Graduate

Research Fellowship.

Joe Talbert for keeping all equipment in working order.

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

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