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1、RADIOSCIENCE,VOL.39,RS1S19,doi:10.1029/2002RS002801,2004AnimprovedionosphericmodelfortheWideAreaAugmentationSystemD.CormierandE.AltshulerRaytheonCompany,Fullerton,California,USAReceived22October2002;revised11June2003;accepted22July2003;published27January2002.[1]Weprovideanenhancedmod
2、eloftheerrorsinducedbydeviationsofionosphericdelaysfromthoseestimatedbytheplanarmodelusedbytheGPS-basedWideAreaAugmentationSystem(WAAS).Toafirstapproximationthenominalionosphericspatialnomdecorrelationofverticalequivalentsignaldelays,sdecorr,isroughlyconstantoverthewholeoftheWAASserv
3、icevolume.However,significantgainsmaybeachievedbynomincludingamoredetaileddescriptionofsdecorrasafunctionofvariousmetricssuchasgeomagneticlatitude,timeofday,aswellasthequalityoftheplanarfitascharacterizedbytheradius,relativecentroidofthefit,andthedensityofdelaydata.Wetakethefirststep
4、inthedevelopmentofthismoresophisticatedmodelbydeterminingwhichofthesenomparametersisbestsuitedforuseasametricfordeterminingsdecorr.Thisallowsustoconstructafirst-ordermodeloftheionosphericdecorrelationwhichdependsonthelocaldensityofionosphericpiercepoints.Ourpreliminarystudyindicatest
5、hatthisfirst-ordermodelwillresultinabetterthan20%reductioninthevaluesofbroadcastgridionosphericverticalerrors(GIVEs)withinthecoterminousUnitedStates.Wealsoobserveabetterthan50%reductionintripsoftheionosphericirregularitydetectorintheAlaskaregion,whichwillleadtosignificantimprovements
6、tocontinuity,althoughthiscomesatthecostofaroughly20%increaseinthemedianGIVEintheAlaskaregion.INDEXTERMS:2447Ionosphere:Modelingandforecasting;6339PolicySciences:Systemdesign;6979RadioScience:Spaceandsatellitecommunication;KEYWORDS:ionosphere,satelliteaugmentation,WAAS,GIVE,SBAS,GPSCi
7、tation:Cormier,D.,andE.Altshuler(2004),AnimprovedionosphericmodelfortheWideAreaAugmentationSystem,RadioSci.,39,RS1S19,doi:10.1029/2002RS002801.1.Introduction[3]Theintegritydataconsistsoftheuserdifferentialrangeerror(UDRE)andthegridionosphericvertical[2]TheWideAreaAugmentationSystem(W
8、AAS)error(GI
