DOC

Measurements of sea ice thickness and its subice morphology analysis using ice- penetration radar in the Arctic Ocean

By Laurie Peters,2014-07-01 03:13
6 views 0
Measurements of sea ice thickness and its subice morphology analysis using ice- penetration radar in the Arctic Ocean

    Measurements of sea ice thickness and its

    subice morphology analysis using ice-

    penetration radar in the Arctic Ocean

CllineseJournalofP0larScience,Vo1.14,No.1,111,June2003

    ;Measurementsofseaicethicknessanditssubicemorphologya-

    ;nalysisusingice?--penetrationradarintheArcticOcean

    ;SunBo(孙波),DengXinsheng(邓新生)’,KangJiancheng(康建成)’,LuoYuzhong(罗宇

    ;)’,WenJiahong(温家洪)’andLiYuansheng(院生)’

    ;JP0ResearchInstituteofChina,Shanghai200129,China

    ;2LaboratoryofIceCoreandCbRegionEnvironment.ColdandAridRegionsEnvironmentalandEngineering

    ;Institute,ChineseAcademyofSciences,Lanzhou730000,China

    ;ReceiveApril15,2003

    ;AbstractBasedonradarpenetratingmeasurementsandanalysisofseaiceinthe ;Arctic0eean.Thepotentialofradarwavetomeasureseaicethicknessandmapthe ;morphologyoftheundersideofseaiceisinvestigated.eresultsindicatethatthera- ;darwavecanpenetrateArcticsummerseaiceofover6metersthick:andthepropa- ;gationvelocityoftheradarwaveinseaiceisintherangeof0.142In?ns_.to0.154 ;In?ns.eradarimagesdisplaytheroughnessandmicroreliefvariationof8ca

    ;icebottomsurface.11hesefeaturesarecloselyrelatedtoseaicetypes.whichshow ;thatradarsurveymaybeusedtoidentifyandclassifyicetypes.Sinceradarimages ;cansimultaneouslydisplaythelinearprofilefeaturesofboththeuppersurfaceandthe ;undersideofSeaice,weusetheseimagestoquantifytheiractuallinearlengthdis- ;erepaney.Anewlen~hfactorissuggestedinrelationtotheactuallinearlengthdis- ;erepaneyinlinearprofilesofseaice,whichmaybeusefulinfurtherstudyofthearea ;differencebetweentheuppersurfaceandbottomsurfaceofseaice.

    ;KeywordstheArcticOcean,radarpenetration,seaicethickness,undersidemot- ;phology,seaicetype.

    ;Seaice.asanimportantcomponentoftheArcticclimatesystem,hasdrawnsignificant ;scientificinterest.Seaicethicknessanditsmorphologyhavedramaticimpactsonocean.at- ;mosphere.iceinteractions(Wadhamsl994;Barryeta1.1993;Dickson1999;Padhamsand ;Norman2000).whichdirectlyaffecttheexchangeprocessandspeedofheatandmassbe. ;tweentheoceanandtheatmosphere,dominatethephysicalmechanicsfeaturesofseaice. ;andaffecttheseaicemovement&deformationaswellasicefreezing&meltingprocess ;(HoHandeta1.1997;HuangandZhang1997;Xieeta1.1995;GooseandFichefet1999; ;Wueta1.1998:SteeleandFlato2000).Intllisrespecttheeffectstudiesofseaicethick. ;nessanditsmorphologyisofcrucialimportance.

    ;Currently.themostusefultechniquesofobtainingseaicethicknessanditsbottomsur- ;facemorphologyareupward-lookingsonarseitherfromsubmarinesormoorings(Hudson ;

    ;

    ;jI{

    ;ii

    ;{

    ;i2sunB..

    ;i{

    ;1990;Kerr1999),thatis,tousesubseasonartomeasuredirectlyupwardattheseaice

    ;icanopy,icethicknessanditsbottommorphologyhavebeenderivedfromsonarimagere

    ;{cordsoficedraftandridgekee1.Drillingsurveyisalsoareliablemethodtomeasureseaice ;thickness,yetitslowefficiencycannotsatisfytherequirementsoflargescalescientificsea ;iceinvestigations.Overthepast10years,withthedevelopmentofspacetechnology,sea ;iceremotesensingdatacanbeobtainedviasatellitesandairbornesurveys.thesedatacan ;generateseaicethicknessanditsmorphologywiththehelpofnumericalmodes(Guoeta1. ;2000;Jineta1.2001;Johanneseneta1.1999).Yetuptonowremotesensingdataisvery ;imprecise.Itisthelackofadequatehighqualitymeasuringdataonseaicevariationsthat ;Iresultsintheinconsistenciesbetweenthearcticandglobalclimatessimulatedbydifferent ;models(Lemkeeta1.1997;HilmerandLemke2000;ZhangandHunke2001;Maslowski ;eta1.2000).

    ;HereweemployedradarpenetrationmethodtomeasureArcticseaicesduringJulyand ;August1999.Theexperimentareacoveredfirstyeariceandmultiyearice.Inthispaper,

    ;weevaluatethepropertiesofradarpenetrationtomeasureseaicethicknessanditsunder- ;sidemorphology,discussthecorrespondingrelationshipbetweenseaicetypesandseaice ;undersidemorphologyreflectedbyradarimages,andanalyzetheareadifferencebetween ;theuppersurfaceandbottomsurfaceofseaice.

    ;I2stIldyareaandmethods

    ;l

    ;ChinagfirstArcticscientificexplorationfromJuly1sttoSeptember9th1999was ;midsummerintheArcticOcean(ChinesefirstArcticexpeditionteam2000).Thetempera

    ;tureoftheexperimentareafluctuatedbetween5.7~Cto+6.C.Seaicewasinthestrong

    ;meltingseasonandsurfacesnowcoverhasalmostmeltedaway.Wechosetypicalicefloes ;tocarlToutradarpenetratingsurveyexperimentanddrillingsurvey.Thesurveyareais ;withinthescopeofN:72.2376.o4,W:153.36164.52.Figure1showsthedistri

    ;butionofsixradarsurveysiteswhosespecificlocationsarelistedonTable1.Seaicetypes ;includefirstyeariceandmultiyearice.Radarsurveyexperimentswereconductedonlevel ;iceuppersurfacesoastoavoidradarwavedistortionscausedbypressureridge.icestack ;andiceuppersurfaceundulation,therebytheseabottomsurfacemorphologywasprominent ;ontheradarimages.

    ;ThesurveyinstrumentisthenewgenerationpulseEKKOIOOAenhancementradarsys

    ;ternmanufacturedbySSI(Sensors&softwareInc.Canada.Havingconsideredbothpene

    ;trationandresolutionperformanceofradarelectromagneticwave,wechosetwoantennas ;withcentralfrequenciesof100MHzand200MHz.Theradarsurveymethodissetupfor

    ;profiling(reflection)mode,whichreceiverantennaandtransmitterantennaarespacedat ;fixeddistancewiththesameequidistantpositionalongprearrangedsurveylinetoobtainra

    ;darprofiles.Theresultofradarsurveyimagesalequalitativestatementsintheformoftwo ;waytraveltimeVersUSreflectedsignalleve1.InordertovalidatethereliabilityofradarSill’-

    ;veyimagetoshowtheicethicknessandtheicebottomsurface.oneortwoCroSSborehole

    ;measurementsweremadeoneachradarsurveyline.Crossboreholemeasurementswere

    ;usedtocomparewithcorrespondingradarsurveydataandprovidenecessarythicknessdata ;toestimateradarwavepropagationvelocityinseaice.

    ;

    ;Measurementsofseaicethicknessanditssubicemorphologyanalysis ;75

    ;C

    ;70

    ;

    ;

    ;Longitude/(.)

    ;Fig.1.Sketchmapofexperimentareafthedotsindicatethe

    ;darsurveysites)

    ;3

    ;Tab

    ;.

    ;1e1?c?Ipsoofradarsurveysite,cross’boreholemeasuredicethickness,radartwo-waytraveltime

    ;3Analysisofradarpenetrationtoseaiceanditspropagationvelocity ;Touseradartomeasureseaicethicknessanddisplayitsbottomsurfacemorphology, ;thekeyliesinthepenetrationperformanceofelectromagneticwavetoseaice,meanwhileit ;alsodependsontheperformanceofradarimagetodisplaytheice/waterinterface.Wecon. ;ductedonsiteexperimenttoanalyzeandtestthepenetrationperformanceofradarwaveto ;seaice.estimatedtherealpropagationvelocityofradarwaveinseaicebycomparing ;radarprofileresultst}lcrossboreholedata.

    ;First,wehaverepeatedtestsonexperimentalseaicesurfacetodetermineradaranten. ;naswithappropriatefrequencyandbestsurveyparameters.Then,weconductedradarfield ;surveysanddrillingsurveysatsixsites.Altogetherabout4kmlongradarsurveyprofileda- ;taand9CroSSboreholesurveydatahavebeencollected.Figure2isatypicalradarimage ;takenatsurveysiteLDoo3.

    ;_;一一0ll一镰0?t..0_?:蠢薯;?{0;:::

    ;

    ;

    ;1

    ;4SunBoeta1.

    ;Position/m

    ;00000

    ;00000

    ;66666

    ;NnIn

;.

    ;20.0

    ;撼蔼潞assumethatthetwowaytraveltimeinTable1isthatradarwaveneededtopene

    ;trateseaice,then,wecanfigureoutthepropagationvelocityofradarwaveviathecross

    ;boreholemeasuredicethicknessandthetwowaytraveltimeofradarwave.?thepropaga-

    ;tionvelocitywasinaccordwithformerstudyresults.thenwecouldexcludethe1stpossibil

    ;ityfortheaboveborderlineinradarimage,thenthe2ndpossibilitybecametheonly ;choice.Soweusetheformula=2h/ts.whereispropagationvelocity,hiscross-bore-

    ;holemeasuredicethickness.tsisthetwowaytraveltimeofradarwavepenetratingseaice, ;tocalculatethetotal9groupdataofthecross.boreholemeasuredicethicknessandCOITe- ;spondingpropagationtimeofradarwave.Theresult(asinTaJ)le1)showsthepropagation ;velocityofradarwaveinmidsummerArcticseaiceiswithintherangeof0.142m?asto ;0.154m?as.Kovas(1998;1986)andMorey(1984)hadanalyzedandcalculatedthe ;propagationvelocityofradarwaveinmidsummerArcticseaiceandtheresultingrangeof ;0.138m?as_.0.160m?as-..Wecanfindthatthepropagationvelocityestimatedin ;thispaperisinaccordancewiththeformerstudies.andthenwecanconfirmthattheclear ;borderlineintheradarimageistheice/waterinterface.

    ;Therefore,aselectromagneticpropertyofseaicedifferssharplyfromthatofseawater, ;thereisobviousdifferencebetweenradarwavepropagationinseaiceandthatinseawater. ;andasharpradarwavereflectionlayerbetweenseaiceandseawaterhasbeenformed.For ;theseaicepart.richreflectingechophenomenonisreflectedinradarimage,whileforsea? ;waterpart.itpresentsthephenomenonofstrongattenuationandabsorption.Itisbecauseof ;theremarkabledifferencebetweentheradarimageofseaiceandthatofseawater(asin ;Figure2)thatthepositionandmicroologyofseaicebottomsurfacecanbecomplete

    ;lvdisplayed.whichadequatelyshowsthatradarwavecannotonlypenetrateseaice,but ;alsovisuallyshowthepositionandmorphologyofice/waterinterfaceinradarimage. ;Cross}-boreholemeasuredicethicknessshowedthatthethicknessofseaiceintestarea ;isbetween2.30mto5.67m.andthethickestvalueisobtainedatLD006.Althoughthe ;thicknessofseaiceintestareawaslimited.wecouldnotobtainthemaximumpenetration ;performanceofradarelectromagneticwaveinseaice.Consideringthatradarimagesdisplay ;goodintensityfeatureofradarwavereflecting

    ;radarequation,wearesurethatiftheproper

    ;arechosen,thepenetratingthicknessofsea

    ;echosignal,combinedwiththeoryanalysisof

    ;frequencyantennaandbestsurveyparameters

    ;icebyradarwaveisatleastover6meters.

    ;=?

    ;;l{?{Ei;:0,..,}0tl4l}t,r?_ji:{}SIl_l.Zl1.’1|_l0?.I_?__0_一州..誓疆簦,雏”;..;

    麓罐薯.氆柚

    ;E\??Q5I3l?Q10Jo?

    ;

    ;6SunBoeta1.

    ;Giventheaveragevelocity0.150m?nsofradarwavepropagationinseaice,basedon

    ;t}levelocitydatainntble1.icethicknesscallbedirectlycalculatedfromradarprofile.Ta.

    ;ble2showstheresultsoficethicknesscomparisonbetweencross.boreholemeasurements ;dataandradarprofiles.FromTable2.weCanseetheerroroficethicknessderivedfrom ;radarprofilesiSnotmorethan5%.SoradarpenetrationsurveyiSeffectiveforseaice ;thicknessmeasurements.

    ;able2of

    ;4Seaicebottomsurfacemicro.Ino

    ;Themorphologyofseaicebottomsurface(ice/waterinterface)includedistributionof ;iceridge(kee1)andrough&fluctuatingmicrorelief.Theyareanintegratorofoceanat-

    ;mosphere0iceinteraction.Themorphologyisasensitiveindicatorofseaicethermodynamic ;growth,icemotion,andmechanicalredistribution.Meanwhile,itmainlyinfluencesthe ;thermohalinecirculationoftheocean,anditisalsothedominantfactorwhichdecidessea- ;waterdragcoefficient(Bjcrgoeta1.1997;BourkeandMclaren1992;TimcoandBurden ;essofseaicebottomsurface,andmadesig-

    ;nificantstudyachievement(Wadhams1988;Kwoketa1.1992;Remundeta1.2O0o).But ;thosestudiesemployedSonarmethodstoconductupwardorsidescantogetanalysisdata. ;DuetolowerresolutionofSonarmeasurement.itcouldonlystudythepressureridgekeelof ;seaicebottomsurface.andthereWasfewrepo~onthestudyoftherough&fluctuatingmi. ;cro.relieffeaturesofseaicebottomsurfaceuptonow.InthisPaper,weusethemethodof ;radarpenetrationsurvey,whoseresolutioniSobviouslybetterthanthatofSonarmethod. ;Notonlycanradarwavedistinguishthedistributionofpressureridgekeelofseaicebottom ;surface.butalsoitcandifferentiatethedevelopingstatusofsmal1.SCalemicro.relief.The ;differencefromthepaststudiesisthatthispaperiSfocusedontheanalysisandstudyofmi. ;cro.relicffeaturesofseaicebottomsurface.

    ;Radarprofilesshowedthatthemicro.morphologyofseaicebottomsurfacecouldbe ;clearlypresentedontheice/waterinterfaceinradarimages.anddifferenttypesofseaice ;displayclearlydifferentmorphology.ForexampleinFig.4.

    ;.__誓盥叠__-lll锄?.}._bll.?=..ll_?.’1蓬雉.;一鬈;

    ;

    ;

    ;20.O

    ;0.0

    ;0

    ;0

    ;0

    ;MeasurementsofSeaicethicknessanditssubicemorphologyanalysis

    ;0

    ;0

    ;0

    ;N

    ;0

    ;0

    ;o

    ;n

    ;00

;00

    ;00

    ;Postition,m

    ;00

    ;00

    ;00

    ;0

    ;0

    ;0

    ;oo

    ;0

    ;0

    ;0

    ;0

    ;0

    ;0

    ;0

    ;0

    ;0

    ;0

    ;

    ;0

    ;0

    ;0

    ;N

    ;0

    ;0

    ;0

    ;n

    ;Fig.4.ComparisionofmorphologyofArcticSummerseaiceboRomsurface(a)ismultiyearice,

    ;(b)isfirst-yearice.

    ;7

    ;Fig.4.includestheradarprofileresultsof(a)multiyearfloeand(b)first-yearfloe.

    ;Fig.4.(a)showsthetoothedandwrinkledfeatureofseaicebottomsurface,whileFig. ;4.(b)showsthatthebottomsurfaceissmoothandflat,andthereisnoknaggychange. ;Fromanalysisoficecorecrystalstructureprofile.wefindtllattheicecoresampledrilled ;from(a)icefloepresentsthecharacteristicsofaltemantdistributionbetweengranularand ;columnicelayerfromtoptobottom.whichcanbeconcludedasatypicalmultiyearicefloe

    ;.

    ;Andtheicecoresampledrilledfrom(b)icefloepresentsalayerofgranularicecrystal ;andalayerofcolumnicecrystalfromtoptobottom,whichbelongstotypicalfirst-yearice ;floe.Themainreasonswhymicro.morphologyofseaicebottomsurfaceunveiledbyradar ;imagescorrespondwellwithseaicetypesasfollows.Thefirstyearseaiceexperiences

    ;shorttimeaffectionbyseacurrentandwindwithinsufficientfreezinganddesalination

;process,hencesmoothbottomsurface;intheprocessofmultiyearicedevelopment,the

    ;actionoflong.timeseacurrentandwindmaketheseaicebottomsurfacecoRPse.Mean

    ;while.withtheprocessoffreezinganddesalinationofseaiceandthechangeoficecompo

    ;nentsandstructures,togetherwiththephenomenonofmeltingwaterinfiltrationandgra~ty ;transferduringseaiceevolvementprocess,themorphologyofknaggybottomsurfaceofsea ;icebecomesmorecomplex.

    ;Basingonthegoodcorrespondingrelationbetweenmicromorphologyofseaicebottom

    ;surfaceandseaicetypes(iceage),andthefactthatradarimagescanclearlydisplaymi

    ;cromorphologyofseaicebottomsurface,weconcludethatradarpenetratingsurveymaybe ;aneffectivemethodtodistinguishfirst.yearandmulti.yearseaicetypes. ;5Differenceanalysisofeffectiveareaofuppersurfaceandbottomsurfaceofmulti

    ;yearice

    ;Itiscommonknowledgethattheuppersurfaceofseaiceistheinterfacebetweenice ;andair,whilethebottomsurfaceistheinterfacebetweeniceandseawater,andontheslogyofknaggyseaicebottomsurfacepresentedbyradarimages,thiskindof

    ;cebottomsurfacemorphologymightprobablyproduceincrescentctivecontactare

    ;abe.

    ;bonomsutrace’wepnnttheradarimageto~ansparencyfilm,makinguseoftheamplifying

    ;mangprincipleofopticsprojection,itiseasytogetthelarge.sizeradarimageswithout ;anydetormationintheprojectioncurtain,thenweCallaccuratelymeasuretheCroSS.section ;lengthotuppersurfaceandbottomsurfaceinterfacesalongtheradarsurveylinewitha ;scale?TheresultsareshowninTable2.

    ;Toquantitativelydescribethedi-erentcross.sec.

    ;tlonlengthofuppersurfaceandbottomsurfaceinterfaces

    ;,

    ;hereweintIDducethecI.0ss.sec.

    ;tionlengthfactorr,whichisdefinedas:

    ;r=(1)

    ;Table3showsthatlengthfactorrisintherangeof1.25to1.35,theaveI.agevalueof ;lengthris1?32,varianceis0.0013,whichadequatelyshowedthattherewasob,ri0usdi

    ;encebehenuppersurfaceandbottomsurfaceinterfacesofseaice.Ifweusedradardsu

    ;Veytomeasureseaice,thenitcouldbecarriedouttoanalyzeandestimatetheaTeadi伍盯ence

    ;between?

Report this document

For any questions or suggestions please email
cust-service@docsford.com