ati underwater acoustics for biologists and conservation managers technical training short course...

8/9/2019 ATI Underwater Acoustics for Biologists and Conservation Managers Technical Training Short Course Sampler

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ATI Course Schedule:

ATI's Underwater Acoustics for Biologists:

Professional Development Short Course On:

Underwater Acoustics for Biologists and Conservation Managers

Instructors:

Dr. William T. EllisonDr. Orest Diachok
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Underwater Acoustics for Biologists and Conservation ManagersA comprehensive tutorial designed for environmental professionals

InstructorsDr. William T. Ellison is president of Marine Acoustics,

Inc., Middletown, RI. Dr. Ellison has over45 years of field and laboratory experiencein underwater acoustics spanning sonardesign, ASW tactics, software models andbiological field studies. He is a graduate ofthe Naval Academy and holds the degrees

of MSME and Ph.D. from MIT. He haspublished numerous papers in the field of acoustics and isa co-author of the 2007 monograph Marine MammalNoise Exposure Criteria: Initial Scientific

SummaryThis three-day course is designed for biologists, and

conservation managers, who wish to enhance theirunderstanding of the underlying principles ofunderwater and engineering acoustics needed toevaluate the impact of anthropogenic noise on marine

life. This course provides a framework for makingobjective assessments of the impact of various types ofsound sources. Critical topics are introduced throughclear and readily understandable heuristic models andgraphics.

Course Outline

1. Introduction. Review of the oceananthropogenic noise issue (public opinion, legalfindings and regulatory approach), current stateof knowledge, and key references summarizingscientific findings to date.

2. Acoustics of the Ocean Environment.Sound Propagation, Ambient Noise

Characteristics.3. Characteristics of Anthropogenic Sound

Sources. Impulsive (airguns, pile drivers,e plosi es) Coherent (sonars aco stic modems

June 15-17, 2010Silver Spring, Maryland

$1590 (8:30am - 4:30pm)"Register 3 or More & Receive $10000 each

Off The Course Tuition."

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Introduction Student Introduction Identify key Interests of Students Course Objectives

Introduction to Marine Mammals from an Acoustic Vi their sounds & hearing and

how they are affected by and respond to anthropogenic

Methods and Tools for Bioacoustic Issues

Metrics Examples of past/present research (may do last!) Bowhead Whales in the Arctic (1980s) SOCAL SRP Tagged Fin Whale (1990s) Stellwagen Bank NOPP (Today)

Tools and Concepts for Evaluating Impacts on the MEnvironment Life Cycle Approach to Environmental Compliance (EC

W


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Key Reference Material

Southall, et al. 2007, Marine Mammal Noise Exposure CritScientific Recommendations

Richardson, et al.1995, Marine Mammals and Noise

Urick, (any ed.) Principles of Underwater Sound for Engine

Harris (ASA Reprint) Handbook of Acoustical MeasuremenNoise Control

Crocker (ASA Pub), Encyclopedia of Acoustics

Kryter (any ed.) The Effects of Noise on Man

Bregman, Acoustic Scene Analysis, MIT Press

ANSI STDs ANSI S12.7 Methods for measurement of impulse noise

ANSI S1.1 Acoustical Terminology

ANSI S1.42 Acoustic Weighting Networks

NRC Reports 2000 Marine Mammals and Low Frequency sound 2003 Ocean Noise and Marine Mammals


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Part I - Introduction to MarMammals from an Acousti

Viewpoint*


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Mystery Sound


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Whale Sounds

&Videos

{Separate Media}


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Marine Mammal Hearingo One of the major accomplishments in [Southall, 2007] was theof recommended frequency-weighting functions for use in asses

effects of relatively intense sounds on hearing in some marine mgroups. It is abundantly clear from:

o measurements of hearing in the laboratory,o sound output characteristics made in the field and in the land

o auditory morphology

o that there are major differences in auditory capabilities across

mammal species (e.g., Wartzok & Ketten, 1999).

o Most previous assessments of acoustic effects failed to accou

differences in functional hearing bandwidth among marine mamgroups and did not recognize that the nominal audiogram mighrelatively poor predictor of how the auditory system responds to

strong exposures.


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Marine Mammal Hearing [Southall, 2007] delineated five groups of fun

hearing in marine mammals and developed ageneralized frequency-weighting (called M-

weighting) function for each. The five groups and the associated designat

(1) mysticetes (baleen whales), designated as lowfrequency cetaceans (Mlf);

(2) some odontocetes (toothed whales) designatedfrequency cetaceans (Mmf);

(3) odontocetes specialized for using high frequencporpoises, river dolphins, Kogia, and the genusCephalorhynchus(Mhf);

(4) pinnipeds, (seals, sea lions and walruses) listenwater (Mpw); and


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Frequency WeightingIn assessing the effects of noise on humans, either an A- or C-weighted curve is applied to correct th

measurement for the frequency-dependent hearing function of humans. Early on, the panel recosimilar, frequency-weighted hearing curves were needed for marine mammals; otherwise, extremhigh-frequency sound sources that are detected poorly, if at all, might be subject to unrealistic cr

al. (2007).

Figure 3.1a below illustrates the A-, B- and C-weighting curves for human hearing (Harris, 1998, Figu

Weigh

for Hum

M

C-FilteFunctio

the M

Filter

Ma

Weight

for Hum

Me

C-FilterFunction

the M-

Filter f

Ma


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M-Weighting

For Marine MammalHearing Metrics: samemathematical structure

as the C-weighting

used in human hearing,

For Marine MammalHearing Metrics: samemathematical structure

as the C-weighting

used in human hearing,

Odontocetes

Southall, 20

assessmenaddressed.

Southall, 2

assessmenaddressed


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M-WeightingThe M-weighting Southall, 2007 developed for the five functional marine

mammal hearing groups has the same mathematical structure as the C-weightin

in human hearing, which reflects the fact that sounds must be more intense at h

low frequencies for them to be perceived by a listener as equally loud. This weig

most appropriate determining the effects of intense sounds, i.e., those with equa

loudness to a tone 100 dB above threshold at 1000 Hz. The M-weighting was de

to do much the same for the different marine mammal groups with the only diff

being the low- and high-frequency cutoffs. The M-weighting for marine mamm

the C-weighting used in humans, rolls off at a rate of 12-dB per octave.The general expression for M-weighting [M(f)], using estimated frequenc

offs for each functional marine mammal hearing group, is given as:

})(max{

)(log20)( 10

fR

fRfM (7) eq.

))(()(

2222

22

lowhigh

high

ffff

fffR

(8) eq.


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M-Weighting (Application)

The applica

Weighting

easily conc

simple filteexample, if

Cetacean w

to a sound

the effectiv

assessmen

could be re

9dB.

-9dB

100 Hz


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Part II - Methods and ToolsBioacoustic Issues

& Analysis


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Bioacoustic metrics and field

Sound source characterization

Sound Types

Pulsed Non-Pulsed

Continuous

Issues include: Effective SL as most are not point sources

(SL=RL+TL)

Energy (Time integration), Peak, RMS??? Band measurements (M-Filter, 1/3 Octave


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Sound source characteriza Sound Types need to be broken down in categor

Pulsed

Non-Pulsed Continuous

Why? Experience has shown that these sound types result in

effects for both injury and behavior Need different metrics like:

SEL,

Peak Pressure or RMS,

Freq. Weighting,

Barotrauma (Acoustic impulse Pa-Sec)


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Pulse vs. Non-Pulse*

The term PULSE is used here to describe brief, broatonal, transients (ANSI 12.7, 1986; Harris, Ch. 12, 1which are characterized by a relatively rapid rise timemaximum pressure followed by a decay that may incperiod of diminishing and oscillating maximal and mi

pressures. Examples of pulses are explosions, gunssonic booms, seismic airgun pulses, and pile driving

NON-PULSE (intermittent or continuous) sounds cabroadband, or both. They may be of short duration,

the essential properties of pulses (e.g., rapid rise-timExamples of anthropogenic, oceanic sources producsounds include vessels, aircraft, machinery operatiodrilling or wind turbines, and many active sonar systeresult of propagation, sounds with the characteristics

at the source may lose pulse-like characteristics at s(variable) distance and can be characterized as a no

t i i (Thi l t i k i t b l


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MetricsPeak sound pressureis the maximum absolute value of the instantapressure during a specified time interval and is denoted as Pmax in u

Pascals (Pa). It is not an averaged pressure. Peak pressure is a use

either pulses or non-pulse sounds, but it is particularly important for c

pulses (ANSI 12.7, 1986; Harris, Ch. 12, 1998). Because of the rapidsuch sounds, it is imperative to use an adequate sampling rate, espe

measuring peak pressure levels (Harris, Ch. 18, 1998).

mean-squared pressure(rms) is the average of the squared pressuduration. For non-pulse sounds, the averaging time is any convenien

sufficiently long to permit averaging the variability inherent in the typebe applied with care to pulse sounds

SPL - Sound pressure levels are given as the decibel (dB) measures

pressure metrics defined above. The root-mean-square (rms) sound

level (SPL) is given as dB re:1 Pa for underwater sound and dB re:

aerial sound. Peak sound pressure levels (hereafter peak) are givere:1 Pa in water and dBpeak re:20 Pa in air. Peak-to-peak soundlevels (hereafter peak peak) are dBp p re: 1 Pa in water and dBp


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MetricsSound exposure level(SEL) is the decibel level of the cumsum-of-square pressures over the duration of a sound (e.g., Pa2-s) for sustained non-pulse sounds where the exposureconstant nature (i.e., source and animal positions are held roconstant), .

For pulses and transient non-pulse sounds, it is extremely usbecause it enables sounds of differing duration to be related total energy for purposes of assessing exposure risk.

The SEL metric also enables integrating sound energy acrosexposures from sources such as seismic airguns and most ssignals.

ref

N

n

T

n

p

dttp

SEL 21 0

2

10

)(

log10


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Source Characterization (

Distributed sources (arrays) require

special consideration Major issue in understanding near field

exposure for large aperture arrays suc

LFA and seismic (early point of conte

Modeling requires near/far field analys

Particle velocity considerations (seism

example)


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HN

RN = [RC2+HN2]1/2

RC

Far Field Criteria

Vertical Line Array of

RFF = RC

[RN-RC ]< /4

SL in the Near field/Far field Regio

SL=SLE+20L

whereNFF = # of elem

Far Fie

SL SL f


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2. Near Field Receive Level Analysis - The analysis required to evaluate the near field of a VLA

accomplished by replacing each nth

element of the N element array with an equivalent point sourc

Pn[R] = {PE/|R-Rn|}{cos(k|R-Rn|) + i sin(k|R-Rn|)} (3)

where,

PE = 10exp[SLE/20] (4)

The resultant pressure, P[R] at the field point R is given by:

P[R] = Pn[R], n=1,N (5)

ote that this is a complex term, and the resultant receive level value, RL in dB, can be arrived at

RL=20Log(|P[R]|) (6)

The difference, RL, between that value and that approximated by simple spherical spreading from

array using the far field SL is given by:

RL= RL-[SL-20Log(|R|)] (7)

The geometry used to evaluate the VLA and relevant coordinate system is shown in Figure 1 alongfor an array of 4 elements.


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Z

Y

Xr

z

R

R=xiX+yiY+ziZR= zniZx=rcos()y=rsin()z=Rcos(r=Rsin(

iZ

iY

iX

Fig 1: Cartesian

Coordinate System

With example showing an Nelement VLA with spacing=d

d

nth

element

R-Rn

zn


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The near field value can also be evaluated in an approximate way by determining the fof each of the embedded subapertures in the array. For example, the far field range for

from 4 elements to 18 is shown in Table 2-1:

Table 2-1 Subaperture Far Field Effects

No. Elements Rff 20Log(N/Rff)

4 6 -4

6 18 -10

8 35 -13

10 58 -15

12 87 -17

14 122 -19

16 162 -20

18 208 -21

20 260 -22

In Table 2-1, RFF was calculated from Eqn 1 for a typical LFAA VLA. The third colum

demonstrates the difference between the element source level and the on-axis receive lusing the subaperture method:

Subaperture Shortcut to Array Near-Field


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Farfield Regi

Focused beam

RL=SLE+20Log(NCan Measure Effe

the array

RL equals SL-TL

Near field Region

Diffuse unfocused beam

Receive Level near HLA = SLECannot Measure Effective SL of

the array

RL not equal to Far-Field SL-TL

Velocity component 3 dimensional

& computed by dP/dx, dP/dy, dP/dz

Effective SL in the Near field & Fairfield Reg

Horizontal LineArray (HLA)

RFF


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150

100

50

0

Array

Horizontal

Axis

Main Response Axis

0 100 200

V ti l R i

lateralDistanceinmeters

Transmitted Near Field Pressure Sound Levels

Low Frequency Multi-Element HLA


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Fig 2-2: Comparing Actual Coherent Array Levels on Axis withthe Far Field Approximation & a SubAperture Approximation

(Element SL=0dB, 20 Elements, Narrowband Signal)

-60

-50

-40

-30

-20

-10

0

10

20

30

Receive

LevelindB

20*log(|Coherent sum|)

20log(N)-20Log(R)

Sub Aperture Approx


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Particle velocity considerations

(single element seismic example

Particle velocity normal direction for the 50Hz so

depth, log scale in cm/secolor scale = -1, Ut = 1x1

Particle velocity in the radialdirection for the 50Hz source at 7m

depth, log scale in cm/sec, i.e. @color scale = -1, uR = 1x10-1 cm/sec


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Examples of

Bioacoustic Researc(Past & Present)

Bowhead Whales in the Arct(1980s)

SOCAL SRP Tagged Fin WhaStell agen Bank NOPP (Tod


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