Primary electromagnetic field in the sea induced by a

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1、WaveMotion43(2005)123131PrimaryelectromagneticfieldintheseainducedbyamovinglineofelectricdipolesEdsonE.S.Sampaio∗InstitutodeGeociˆenciasdaUFBA,Sala213B,CampusUniversit´ariodeOndina,40170-290Salvador,Bahia,BrazilReceived19January2005;receivedinrevisedform1

2、2July2005;accepted8August2005Availableonline3October2005AbstractTheanalysisoftheprimaryelectromagneticfieldscausedbysteadystateortransientelectriccurrentflowingalongacableoffinitelengthmovingwithaconstantvelocitybelowtheseasurfacehasseveralapplications.Itsu

3、pportstheanalysisofsubmarinephysicaldataanditisusefulforprotectingshipsfromthethreatofseamines.Theusualapproachtodescribetheprimaryfieldstartsfromthesolutionofamagneticvectorpotentialinthefrequencydomainduetoanelectricdipole,whichisobtainedwiththemethodof

4、Green.SubsequenttransformationtothetimedomainemployingLaplacetransformaswellasintegrationalongthecablelengthallowstodescribethetimevariationoftheprimaryelectromagneticinducedfieldduetoalineofelectricdipoles.Theresultisapplicabletobothshallowanddeepseawate

5、renvironments.Becauseofthedifferenceinvelocitybetweensourceandreceiver,acarefulapplicationoftheconvolutionintegralisnecessaryinordertoadaptthesourcepulsesolutiontoanytypeoftrans-mittingcurrentwaveform.Furthermoreitisshownthattheinfluenceoftherelativeveloc

6、itybetweensourceandreceiverisnotnec-essarilynegligible.Thereforeithastobeconsideredintheinterpretationofthesecondaryfieldsscatteredbygeologicalfeatures.©2005ElsevierB.V.Allrightsreserved.Keywords:Electromagnetic;Sea;Movingsource;Lineofdipoles1.Introductio

7、nTheanalysisofelectromagneticfieldscausedbysteadystateortransientelectriccurrentflowingalongacableoffinitelengthplacedinseawaterhasseveralapplications.Itsupportstheanalysisofsubmarinephysicaldataforenvironmentalandshallowordeepcrustalresearch,anditisalsouse

8、fulforprotectingshipsfromthethreatofseamines.Duringthelasttwodecadespracticalandtheoreticaleffortshaveledtothedevelopmentofcontrolledsourceelectromagneticinduction(EMI)techniquesforsurveyingtheseasubstractum:[3,5,6,8,10].P