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ID:40386116
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页数:5页
时间:2019-08-01
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1、DEVELOPMENTOFAPRACTICALCOHERENTACOUSTICDOPPLERCURRENTPROFILERRamonCabreraandKentDeines'BlairBrwnleyandEugeneTerray''RDInstruments,9855BusinessparkAve.'WoodsHoleOceanographicInst.SanDiego,CA92131WoodsHole,MA02543ABSTRACT2.REVIEWOFDOPPLERSONARSThepracticalfeasibilityofdevelo
2、pingaIncoherentDopplersonar:CoherentAcousticDopplerCurrentProfiler(ADCP)withspatialresolutionandrangeConventionalincoherentADCP'sestimatethecomparabletothoseofcommerciallyavailableDopplershiftfromsinglepulseechoes.Theincoherentsystemsbutwithmuchsmallertransmittedwaveformis
3、typicallyaperiodicvelocitymeasurementvarianceisbeingpulsetrain,sothatthemaximumrange'is1/2studied.Thisimprovementinmeasurementthepulseinterval(inunitswherethespeedaccuracywillreducerequiredaveragingtimes,ofsoundistakentobe1).Rangebinsarethuspermittingtheobservationofshortt
4、ime-definedbytime-gatingthereceivedsignal,scalecurrents(i.e.internalwavebreaking)andthelengthofthegateisusuallymatchedwhicharebeyondthecapabilitiesofavailabletothepulselengthT,givingarangeincoherentADCP's.SeveralstrategieshaveresolutionofT/2.Theradialcomponentofbeenanalyse
5、dandtested.Amongthem,trans-thevelocityofthescatterersinaparticularmissionofcodedacousticpulsescombinedwithbinisrelatedtotheDopplershiftF,by:coherentsignalprocessingtechniqueshasbeengivenspecialattention.ThisapproachmayU=0.5XFD(1)allowthemeasurementofwatermassvelocitieswith
6、highaccuracywithouttherangewhereXistheacousticwavelength(forlimitationsofconventionalpulse-to-pulseexample,X=0.5cmat300kHz).coherentsystemsduetovelocityambiguityandpulse-to-pulsedecorrelation.SeveralschemesAlowerboundonthevarianceoftheDopplerbasedonthisapproachhavebeenanal
7、ysedandfrequencyestimatefromasinglepulseistheirrelativemeritsassessed.givenbytheCramer-Raobound,which€oranunbiasedestimatorisapproximatedby:UF=(2nTI-l(1+36/SNR+30/SNR2)'(2)1.INTRODUCTIONwhereSNRisthesignal-to-noiseratiooftheDopplerreturn(Theriault,1986).ThisRI,Instruments(
8、RDI)iscurrentlystudyingthefunctionisplottedinFigure1(thecurvefeasibilityofdevelopinganewg
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