development of doppler current profiler

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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