ambient noise modelling - ocean frontier institute · 2018. 10. 30. · david barclay, dalhousie...
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Environmental and ship noise
measurements and modelling
David Barclay,
Dalhousie University
August 30th, 2018
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Wenz curves - data derived modelSources of ambient noise
National Research Council. 2003. Ocean Noise and Marine Mammals. National Academy Press, Washington, D.C. (as adapted from Wenz, 1962) by the National Academy of Sciences
1 10 100 1000 10 000
f [Hz]
Wind
Dependent
Noise
Distant
Shipping
Noise
Precipitation Noise
Earthquakes and
explosions
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Ship noise footprint modelling
Input data needed:Ship position(s)Source levelBathymetrySeabed acoustic propertiesWater column structure
Output:Noise level (x,y,z & freq)Sound exposure level
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Sound Speed [m/s]
Dep
th [
m]
Range [km]2000
Favorable Arctic conditions
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Bathymetry m
Noise level distributions of surface wind generated noise
NSL: mean(|p|2/A)=10-5(Pa)2, std=10-4(Pa)2
Nx2D
zr = 50 m
Noise modeling
Noise level distributions in canyonHudson Canyon Bathymetry – sources at 0.1 m
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Bathymetry m
Noise level distributions of surface wind generated noise
3D
zr = 50 m
Noise modeling
NSL: mean(|p|2/A)=10-5(Pa)2, std=10-4(Pa)2
Noise level distributions in canyonHudson Canyon Bathymetry – sources at 0.1 m
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Ideal ambient noise model
Captures:• Source physics, distribution statistics, surface
wind, wave, and current information.• Bathymetric effects, 3D when necessary• Accurate bottom acoustic properties• Depth and range water column variability • Non spatially uniform processes
Precipitation, ice noise, surf noise Implementation:
• Portably validatedOutput:
• Probability power spectral density• Spatial properties (directionality, coherence)
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Wave generated surface noise models
Surface source strength:
WOTAN method relating wind speed to band averaged spectral level is most physics based work available.
Extend this work to shallow water and the ‘arbitrary ocean’
Directionality can be found using PE or normal modese.g. Kuperman & Ingenito, Buckingham & Deane
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Vertical coherence and directionality
G12(w) =1
2F(q)e
-iwd
cCos(q )
0
p
ò Sin(q)dq
Vertical coherence Vertical noise directionality
We can very accurately model coherence (directionality) without the uncertainty of source level.
We can determine exactly the relative contributions of wind & shipping to the noise field, as a function of time & frequency.
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Time series of vertical coherence
April 6 May 4Date
Imaginary vertical coherence
Real vertical coherence
Freq
ue
ncy
[H
z]Fr
equ
en
cy [
Hz]
Alvin Canyon, 2016W
ind
no
ise Time varyin
gsh
ip n
oise
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Co
he
ren
ceC
oh
ere
nce
Frequency [Hz]
Wind
Wind + 10 km ship (10 modes)
Wind + 10 km shipData
0 1000 2000 3000 4000 5000
Wind and distant shipping modelling
G12wind+shipping =
G12wind + C*G12
shipping
Fit is performed by searching over C
Data–model fitting allows estimate of effective range and relative power.
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Partitioning of wind and shipping noise
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noise.phys.ocean.dal.ca/barrow/bsrto/
Data collected by DFO
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noise.phys.ocean.dal.ca/barrow/bsrto/
Data collected by DFO
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Model & measurement campaign
Data• Acoustic data: Multi-month measurements on vertical pairs of hydrophones• Meta-data: SSP, bottom loss, wave buoy, AIS, wind speed & dir., precipitation
radar, barometer, humidity, upward looking ADCP• Modeled meta-data: wind speed & dir, SSP, surface currents
Research Objectives• Collect a data set to validate a portable environmental & ship noise model • Perform sensitivity analysis of the noise model using modeled meta-data• Produce bioacoustic metric maps
Technical goals• Reproduce observations for ambient and ship noise to determine source level
model accuracy.• Determine conditions when horizontal scattering and refraction must be
considered• Apply this model in the arbitrary ocean by evaluating against data sets of
opportunity.
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• Ship tracking (non-AIS tagged)
• Source level uncertainty
• Transmission loss– Model input data
– Ambient noise model
• Bioacoustics…!– Animal distributions
– Marine animal hearing sensitivity
– Behavioral & physiological response
Major challenges ahead
Starting work here…
ECHO project
Need northern community involvement.
Collective effort & hard…