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OceanAcousticsOceanislargelyopaquetoEMradiation…butsoundpropagateswellConsider: propagationspeed refraction,reflection scattering,attenuation rangeApplicationsCrowdsourcingwhalesonganalysisSoundintheocean:OceanAcousticsOceanislargel1In1826,JeanDanielColladonusedachurchbellunderwatertoprovethatsoundtraveledfasterthroughwaterthanair.InlakeGeneva,assistedbyCharles-FrancoisSturm,amathematician,thetwosplitapartby10milesinboats.Onestruckthebellunderwaterandignitedgunpowderabovethesurfaceatthesametime.Theotherstartedatimerattheflashofthegunpowderandstoppedthetimerwhenthesoundarrived,

usingatrumpet-like

instrumenttodetectthe

underwaternoise.Despite

theirsimpledevices,they

calculatedthespeedof

soundunderwaterat

1435m/s.In1826,JeanDanielColladon2

Constantsoundspeed

meansnorefractionSpeedofsoundinseawaterisabout1500ms-1Soundpropagatesbycompressionandrarefactionofacompressiblemedium.Waterisnotverycompressible,sothespeedismuchhigherthaninair(340ms-1)Affectedby:PressureTemperatureSalinityConstantsoundspeed

means3Itcanbeshowninthecaseofaconstantsoundvelocitygradient,dc/dz,thatthesoundraydescribesanarcofacirclewhoseradiusis:Sincesoundvelocityisnotconstant,soundraysfollowcurvedpaths.TheyarerefractedfollowingtherelationshipgivenbySnell’sLaw:Itcanbeshowninthecaseof4Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学5Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学6SOundFrequencyAndRanging(SOFAR)channelRAFOSfloatSOundFrequencyAndRanging(S7Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学8Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学9Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学10Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学11Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学12Fromapointsource,soundspreadssphericallyandintensityfallsproportionaltoR2

TransmissionlossSomesoundreachesthebottomandisreflected,sothetransmissionlossisdecreasedOververylongdistances,withmuchoftheenergytrappedinthesoundchannel,thespreadingiscylindricalandtransmissionlossisproportionaltoRFromapointsource,soundspr13SoundintensityindecibelsSoundLevelintensityisdescribedinnon-dimensionalunits(relativetoareference)onalogscaleindecibels

SL=10log(I/Iref)=20log(p/pref)

Factorof10becauseitisdecibels,notbels

Factorof20becauseintensityIisproportionaltop2

A10dBincreasemeansanorderofmagnitudeincreaseinsoundintensity

Thereferencepressureinwateris1microPascalSoundintensityindecibelsSou14humanvoice

80-3000Hzbaleenwhales

10-50Hzhumanvoice

80-3000Hzbaleen15Attenuationisthecombinationofabsorptionandscattering.Absorption:duetomolecularpropertiesofwaterandincreaseswithsquareofthefrequencyScattering:lackofhomogeneityoftheocean–temperaturemicrostructure,airbubbles,plankton,particulates…Essentiallyallattenuationisbyabsorptionatfrequencies>500Hz

Forcomparison,attenuationof10kHzsoundinmoistairisabout160dB/km;intheoceantheattenuationlossforthesamefrequencyisabout1dB/km.1000Hz:air5db/km,water0.05db/kmAttenuationlossAttenuationisthecombination16Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学17Normalizedacousticalcross-sectionforanairbubbleinwater,andforarigidsphereofthesameradius,R.Thepeakcorrespondstoanaturalresonantfrequencyof52kHz.Airismorecompressiblethanwater,andairbubbleshavenaturalresonantfrequenciesdependentontheirsize.Fishhaveair-filledsacscalledswimbladdersthatareroughlyellipsoidalinshapeandwhichcanpresentaresonanttargettosonar.Normalizedacousticalcross-se18Thedifferencesinswimbladderscausedifferencesinthereturnechoofasonarsignal.Echosignaturesforspecificspeciescanbedeterminedandusedtoidentifyfish.FishfinderdisplayThedifferencesinswimbladde19:///StraitofGeorgia-EastNode-24Hours-ZooplanktonAcousticProfiler(ZAP)8pm8am:///StraitofGeorgia-Ea20StraitofGeorgia-EastNode–24hoursdatafromZooplanktonAcousticProfiler(ZAP)8pm8am

StraitofGeorgia-EastNode21Ocean-Acoustics---Rutgers-University：海洋声学-罗格斯大学22Acoustictransmitters(tags)forthisprojectproducesoundat67KHz(aboveaudiblerangeforhumans)

Acoustictagsaresurgicallyimplantedinstripedbass.Haveawaxcoating,topreventimmunesystemfromrejectingit.Two-yearbatterylife.Transmitter"pings"anidentifyingcodedetectablebyhydrophonesupto500maway.Hydrophones(underwatermicrophones)arehungfrombuoysatfixedlisteningcheckpoints,throughouttheMullicaRiver/GreatBayEstuary.Checkpointsareplacedmostlyatnarrowpassages,suchasLittleEggInlet,sothatfishmustpassthroughtheminordertomoveupordownriver,orintooroutofthecoastalocean.EnvironmentaldatafromREMUSAUVsandmooredinstrumentsarecomparedtothestripedbass'movementpatternsAcoustictransmitters(tags)f23AcousticTomographyAnetworkofacousticsourcesandreceivershasmultiplehorizontalpaths(inadditiontomultipleraysinsoundchann

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