april 20, 2011
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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
NNMREC
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
NNMREC
Ambient Noise SourcesBedload TransportShip
AverageConditions Quiet
NNMREC
Ambient Noise CharacteristicsCumulative Probability
DensityHydrophone Deployments
Temporal variability dominates over spatial variability
NNMREC
Strong CurrentsOvernight Lull in Shipping
First Run for Passenger Ferry
Recording Hydrophone
Automatic Identification System
DopplerProfiler
Establishing Context for Observations
NNMREC
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
NNMREC
Data Assimilation
SPL (
dB re
1 μ
Pa)
Distance to closest vessel (km)
Vessel Proximity Noise Correlation
Vessel noise drives broadband noise levels
Source: Chris Bassett, forthcoming PhD dissertation
NNMREC
Sound during High Currents
Hydrophone Response
Current Velocity
NNMREC
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
NNMREC
Pseudo-Sound Identification
Unshielded Hydrophone
Hydrophone with
Flow Shield
Source: Chris Bassett, forthcoming PhD dissertation
NNMREC
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
209D
f (Hz) (Thorne, 1986)
Source: Chris Bassett, forthcoming PhD dissertation
NNMREC
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
NNMREC
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.
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