测绘外文文献Word格式文档下载.docx

测绘外文文献Word格式文档下载.docx

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测绘外文文献@#@MODERNGEODETICREFERENCEFRAMESFORPRECISESATELLITEPOSITIONINGANDNAVIGATION@#@J.KoubaandJ.Popelar@#@GeodeticSurveyDivision,GeomaticsCanada,NaturalResourcesCanada（NRCan）615BoothStreet,@#@Ottawa,Ontario,CanadaK1AEO9@#@E-mail:

@#@**************.ca;@#@****************.ca@#@ABSTRACT@#@TheNAD83andWGS84referencecoordinateframeswereestablishedmorethanadecadeagotosatisfymostmapping,charting,positioningandnavigationapplications.Theyareconsistentatthe1-2metrelevelonacontinentalandglobalscalesrespectively,reflectingthelimitationsofavailabledataandtechniques.Withrapidimprovementsinpositioningaccuracy,mainlyduetoGPS,submetrenavigationhasbecomepracticalandreferenceframesatthecmtommlevelarerequiredbythemostdemandingusers.TheIERSTerrestrialReferenceFrame（ITRF）wasestablishedin1988bytheInternationalEarthRotationService（IERS）tofacilitateprecisemonitoringoftheEarthOrientationParameters（EOP）basedonstate-of-the-arttechniquessuchasVeryLongBaselineInterferometry（VLBI）andSatelliteLaserRanging（SLR）.WiththeestablishmentoftheInternationalGPSServiceforGeodynamics（IGS）in1994,theITRFisdirectlyaccessibletousersworld-widebymeansofpreciseglobalGPSsatelliteorbit/clocksolutionsandalargenumberofIGSmonitoringstations.ThemostrecentITRFsolutions,designatedITRF92andITRF93,arebasedonspacegeodeticobservationsincludingGPSuptotheendof1993providingglobalconsistencyatthecmlevel.TheCanadianActiveControlSystem（CACS）facilitatesaccesstoITRFthroughactiveparticipationinIGSandVLBI.FiducialVLBIpointsincludedinNAD83provideadirectlinktoITRFandmakeitpossibletoupgradeNAD83coordinatesinordertosatisfypositioningandnavigationrequirementswithcmprecisioninthefuture.CACSfacilitatesthemostefficientconnectionstotheITRFandNAD83referenceframesforhighprecisionpositioningbyGPSaswellasforgeneralspatialreferencingneedsinCanada.@#@1.INTRODUCTION@#@Ingeodesyareferencecoordinateframeimpliesascale,orientationandcoordinateoriginaspartofareferencesystemwhichalsoincludesEarthplanetarymodelsandconstantsnecessaryforsatelliteorbitdetermination,ge-odynamicandgeophysicaldataanalysis.Satellitenavigationsystemsmadeitpossibletoestablishatrulyglobalgeocentricreferencesystemwhichwasquicklyadaptedforprecisegeodeticpositioning,especiallyoverlongdistances.Forthefirsttimeitwaspossibletodeterminedistortionsandmisorientationofclassicalgeodeticnetworksaroundtheworld.TheU.S.NavyNavigationSatelliteSystem（NNSS）,alsocalledTransitorsimplyDoppler（KershnerandNewton,1962）becamethebasisfortheU.S.DepartmentofDefenseWorldGeodeticSystem1972（WGS72）andlaterWGS84whichdefineglobalgeocentricreferenceframesconsistentataboutthe1-2metrelevel.ToupgradeandcorrectdistortionsoftheclassicalNorthAmericanDatum1927（NAD27）,areadjustmentofthegeodeticnetworksinCanada,USA,MexicoandGreenlandwasjointlyundertaken.Thisnewdatum,designatedNAD83,wasnominallymadecompatiblewithWGS84bybeinggeocentricandorientedaccordingtotransformedDopplerpositions,butinadditiontheNAD83adjustmentincludedVLBI（VeryLongBaselineInterferometry）baselines.Thusboth,WGS84andNAD83,areconsistentataboutonemetre,mainlyduetothelimitationsoftheDopplertechniques（Kouba,1993）.GPSandotherspacebasedtechniquessuchasVLBIandSatelliteLaserRanging（SLR）providedatawithhigherprecisionstosupportstudiesofcrustaldynamicsandpolarmotionwhichrequireamoreaccurateglobalreferenceframe.TheIERSTerrestrialReferenceFrame（ITRF）wasestablishedin1988andisupdatedonanannualbasisbytheInternationalEarthRotationService（IERS）tokeepitcurrentandtoimproveknowledgeofstationvelocitieswhicharenecessaryformaintainingtheaccuracyofthisglobalreferenceframe.NAD83canberelatedtoITRFpreciselyforagivenepochbyatransformationbasedoncommonVLBIstations.TheCanadianActiveControlSystem（CACS）providesthemostefficientmethodtoupgradeNAD83coordinatesinCanadainordertomeetpositioningandnavigationrequirementswithcmprecisioninthefuture.@#@2.NORTHAMERICANGEODETICDATUM:

@#@NAD83@#@TheNorthAmericanDatum1927（NAD27）wasestablishedatthebeginningofthiscenturyusingcontinentaltriangulationwithacentrallylocateddatumpointatMeadesRanchinKansas,USA（Ross,1936）.Satellitegeodesyinthe60'@#@sand70'@#@sdetectedtheapproximately100moffsetoftheNAD27originwithrespecttothegeocenteraswellasdistortionsexceedingtensofmetersinsomepartsofthegeodeticcontrolnetwork（Mueller,1974）.Anewreferenceframewasrequiredtofacilitateuseofefficientandprecisesatellitegeodetictechniques