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1、th40AnnualPreciseTimeandTimeInterval(PTTI)MeetingTIMETRANSFERFROMCOMBINEDANALYSISOFGPSANDTWSTFTDATAPascaleDefraigneRoyalObservatoryofBelgium(ROB)AvenueCirculaire,3,B-1180Brussels,BelgiumE-mail:p.defraigne@oma.be12M.CarmenMartínezandZ.Jiang1UniversityofAlicant
2、e,Spain,E-mail:carmen.martinez@ua.es2BureauInternationaldesPoidsetMesures,France,E-mail:zjiang@bipm.orgAbstractThispaperpresentsthetimetransferresultsobtainedfromthecombinationofGPSdataandTWSTFTdata.Twodifferentmethodsareusedforthecombination:afirstone(namedC
3、V+TW)isbasedonaleast-squaresanalysisofGPScodeandcarrier-phasemeasurementsincommonview,constrainedbyTWSTFTdata.UsingtheVondrak-Cepekalgorithm,thesecondapproach(namedPPP+TW)combinestheTWSTFTtimetransferdatawiththeGPSclocksolutionscomputedwithPrecisePointPositio
4、ning.CombiningGPSandTWSTFTconsiderablyincreasestherobustnessoftheaccuratetimetransferresultduetothecompleteindependencebetweenthetwospatialtechniques.Bothcombinationmethodsprovideatimetransfersolutionwhichbenefitsfromthehighshort-termstabilityandhighresolutio
5、noftheGPSdataandthehighaccuracyoftheTWSTFTdata.ThePPP+TWsolutioniscontinuous,whilesomediscontinuitiesexistinthesolutionCV+TW,duetothenoiseanddiurnalperturbationintheTWdata.Ingeneral,thesolutionsobtainedwithbothmethodsagreewellwitheachother.Ther.m.s.ofthediffe
6、rencesbetweentheresultsremainsbelow300picosecondsforthelinksinvestigated.INTRODUCTIONThetwomaintechniquespresentlyusedforaccuratetimetransferare«Geodetictimetransfer»basedonthejointanalysisofGPScodeandcarrier-phasemeasurements,togetherwithaconsistentmodelingo
7、fthesemeasurementsand«Two-WaySatelliteTimeandFrequencyTransfer»(TWSTFT),whichisbasedonmeasurementsoftransittimeofsignalstravelingsymmetricwaysbetweenthetwoclockstobecompared.Whilegeodetictimetransferiswidelyrecognizedforitshighfrequencystability(see,forinstan
8、ce,[1-3]),anditshighresolution,itis,however,limitedbythecoloredsignatureofthecodenoise,affectingthemedium-termstabilityofthesolutionandinducingpossiblediscontinuitiesatthedayboundaries[4]
