衛(wèi)星導(dǎo)航系統(tǒng)SatelliteNavigationSystem任課教師：趙琳課程內(nèi)容Syllabus§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述§2

GPS系統(tǒng)組成§3GPS定位原理§4GPS信號(hào)與導(dǎo)航電文§5GPS系統(tǒng)誤差分析及補(bǔ)償§6GPS應(yīng)用§1

衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述IntroductiontotheDevelopmentofSatelliteNavigation§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述HistorychangedonOctober4,1957,whentheSovietUnionsuccessfullylaunchedSputnikI(СпутникI).Thatlaunchusheredinnewpolitical,military,technological,andscientificdevelopments.1.1.人造衛(wèi)星的發(fā)射使衛(wèi)星導(dǎo)航成為可能SputnikI§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述On4October1957,launchofSputnikI.On3November1957,SputnikIIwasputintoorbit.SputnikIIIwaslaunchedon18September1958.OrbitofsputnikI,II,III§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述AtAppliedPhysicsLab(APL),JohnsHopkinsUniversityatBaltimore,twojuniorphysicists,GeorgeWeiffenbachandWilliamGuier,wereregardedastheGENESIS&PIONEERSOFSATELLITENAVIGATION.TheyfiguredoutawaytodetermineSputnik'sorbitsimplybymeasuringtheDoppler-inducedchangesinthefrequency.

George(left)andWilliam(right)

atarecentsymposiumontheLegacyofTransit.§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述JohaanChristianDoppler,anAustriaphysician,foundDopplerEffectin1842.

JohaanChristianDoppler1803-1853

DopplerShiftisaneffectthatisassociatedwithanywavephenomena(suchassoundwaves).§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述DopplerShift§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述ROYGBIV：Red,Orange,Yellow,Green,Blue,Indigo,Violet

Ifyoudriveyourcarto

movesoquicklytowardsaredtrafficlightthatitwouldappeargreentoyou,willthepolicefineyou?§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述JohnsHopkinsUniversitysignedacontract(PlanTRANSIT)withAmericanNavyin1960;NavyNavigationSatelliteSystem(NNSS)wasbuiltupinJanuary1964;1.2.子午儀計(jì)劃（PlanTRANSIT）§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述RichardB.KerschnerAwardThisawardisfortherecognitionofanindividualwhohasmadeasubstantialcontributiontothetechnologyofnavigationandpositioningequipment,systems,orpractices.Initiatedin1986,itispresentedatthebiennialPositionLocationandNavigation(PLANS)Conference.

WilliamH.Guier,FrankT.McClure,andGeorgeC.

Weiffenbach(ltor)discusstheprinciplesoftheTransitNavigation

System(latercalledtheNavyNavigationSatelliteSystem).§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSTransitConstellation§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSTheOrbitIntervalofTRANSITsatellite§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSTheOrbitofTRANSITsatellite§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSTwoNNSSSatellites§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSNNSSReceiver§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSSNavigationPrinciple§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NNSSNavigationPrinciplet1t2t3OrbitD1D2D3§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NNSSNavigationAccuracy

In1967,thesystemwasopenedtothecivilapplicationoftheworld;In1968,theaccuracyofNNSS:~70mIn1976,

itwasimprovedtobe:~30m§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述In1967,VicePresidentHubertHumphreyreleasedthesystemforpublicandcommercialusebyshipsofallfriendlynations,andinOctoberhepresentedDr.KershnerwithaDistinguishedPublicServiceAward.

Attheendof1996Transit,theNavyNavigationSatelliteSystem,wasretiredaftermorethan32yearsofcontinuous,successfulservicetotheU.S.Navy.Duringits32yearsofoperation,theTransitNavigationSystemprovidedanextremelyaccurateandreliableglobalnavigationsystemfortheU.S.Navyandtheciviliancommunity.Thesystemwascontinuouslyimprovedthroughtheyearsandcontributedtonumerousadvancesinspacescience,engineering,andtechnology.NavyNavigationSatelliteSystem—NNSS§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述TheTransitsystemspawnedanumberofspace"firsts,"includs:thetwo-frequencymethodforcorrectingionosphericerror,solarattitudedetectors,dual-launchpayloads,satelliteelectronicmemoryanuplinkauthenticationsystem,gravity-gradientstabilization.developmentofsatellitecompensationfordragandradiationpressure,theuseofpulsedplasmamicro-thrusters,andhardeningofthespacecraftagainstanenhancedradiationenvironment.§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NavyNavigationSatelliteSystem—NNSS1.3NAVSTARGPSNAVigation

SatelliteTimingAndRangingGlobalPositioningSystemDevelopedandmaintainedbytheDepartmentofDefenseOperatestwopositioningservicesPrecisePositioningService(PPS)StandardPositioningService(SPS)Consistsofthreesegments:User–handheldreceiverSpace–satelliteconstellationControl–trackingandcorrections

§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述NAVSTARGPSGenerationsofthecurrentsystemBlockISeriesof11experimentalsatellites1stsatellitelaunchedin1978,thelastin1985Lastsatellitedecommissionedin1995BlockII/IIAlaunched1989-19974atomicclocksIncreasedsatellitelifetimeMoredatastoragecapabilitiesNucleardetonationdetectorBlockIIRAbilitytooperateautonomouslyforlongperiodsUpto5carriersignals§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述CurrentGPSCapabilitiesThecurrentsystememploys24activesatellites,atleast6backupsCosttomaintainsystem:$750millionperyearCombinationofBlockII,IIAandIIR1995useofGPSbecameavailabletothepublic,freeofchargeLevelsofservice:SPSchannelL1Predictedaccuracy:13mhorizontal,22mvertical,200nsPPSchannelL2Predictedaccuracy:8mhorizontalandvertical,40ns§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述1.4OtherSystemsGLONASSBeidouGalileoWAASLAASEGNOSMSAS§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GLONASSGlobalNavigationSystemdevelopedbyRussiaNominallyconsistsof21satellitesplus3spares8satellitesarrangedin3orbitalplaneswithaninclinationof64.8oOrbitsareapproximatelycircularwithaperiodof11h15m§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GLONASSAlsotransmitsL1&L2carriers,C/A&PcodesL1isin1602-1615.5MHzbandTobeshiftedto(1598.0625-1604.25MHz)L2isin1246-1256.5MHzbandTobeshiftedto(1242.9365-1247.75MHz)C/Acodeis0.5MpsPCodeis5.11Mbps§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GLONASSCarrierfrequencydependsonthesatelliteEachoneiscurrentlyuniqueAftershift,eachpairofsatelliteswillbeassignedthesamefrequencyPairsonoppositesidesoftheEarth(antipodal)Usesfrequencychannelratherthancodetoidentifysatellite§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GLONASSThesystemisnotasrobustaspredictedEconomiccrisishasseverelyhurttheRussianspaceprogramFewersatellitesinorbitthanexpectedAslittleas7inMay2001Newclassofsatellites(GLONASS-M)shouldbelaunchedsoon§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GLONASSCanbeusedinconjunctionwithGPStoimprovenavigation/positioningNeedtoaccountfor2differencesinreferenceNeedtotransformEarthParameterSystem1990(PZ-90)toWGS84Candifferbyupto20mNeedtorelateRussiantimescaletoGPStimeCandifferby10sofμs§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述Beidou北斗系統(tǒng)ChineseregionalsatellitenavigationsystemConsistsof2satellitesingeostationaryorbitsAltitudeof36000kmUsedinlandandmarinetransportationPlansfornextgenerationsystem§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述地面中心站S1S2D1D2DS1DS2用戶北斗系統(tǒng)§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GalileoSystem伽利略系統(tǒng)

SystemSpecification：PositioningAccuracy:10m(95%);TimingAccuracy:<33ns;TTFF:<15s;GlobalAvailability:>99.7%;30satellites;

§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述系統(tǒng)將耗資24~30億歐元；推行公方和私方聯(lián)營(yíng)體制（PublicPrivatePartnership）；中國(guó)已于2003年9月18日正式成為該系統(tǒng)的投資方。Galileo§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GalileoProposedandbeingplannedbyEuropeItwillbecontrolledbyciviliansPlanscallfor30mediumEarthorbitsatellitesDistributedin3orbitalplanesAltitudeof23000km§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GalileoWillprovide2levelsofserviceBasic(free-of-charge)Chargeableservice3phasesofdevelopmentDefinitionphase(alreadycompleted)DevelopmentandvalidationphaseDeploymentphaseScheduledtobeginin2006/7timeframeServiceby2008(?)§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述GalileoBecauseitiscivilianoperated,itwillhaveadvantagesinthemarketplaceAlreadypromisingtoprovideaservicethatwillmeetlegalstandardsGPScan’tdothisIfthelawyersarehappy,thebusinessmoneyismorelikelyintoGalileoproducts§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述WAASWideAreaAugmentationSystem(WAAS)CoversNorthAmericaSouthAmericacouldbecoveredlaterUtilizesGPSbutaugmentsitwithadditionalsatelliteinformationUsegeostationarysatellitesInternationalMaritimeSatellite(Inmarsat)ProvidesadditionalreliabilityandaccuracyUsedforaircraftnavigationNotnecessarilyfortakeoffandlanding§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述LAASLocalAreaAugmentationSystem(LAAS)UtilizesGPSbutaugmentsitwithpseudoliteinformationatcriticallocationsTypicallyaroundairportsbutcouldbeusedinotherlocationstheoreticallyUsedforaircrafttakeoffandlandingIncludingcategoryII/III§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述EGNOSEuropeanGeostationaryNavigationOverlaySystem(EGNOS)EuropeanversionofWAASCoversallofEuropeandNorthAfricaCouldbeextendedtocoverallofAfricaandMiddleEastWilleventuallybesupercededbyGalileo§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述MSASMTSATSatellite-BasedAugmentationSystem(MSAS)Multi-functionalTransportSatellite(MTSAT)JapaneseversionofWAASCoverspartsofAsiaandthePacific§1衛(wèi)星導(dǎo)航系統(tǒng)發(fā)展概述§2GPS系統(tǒng)組成GPSSystemComposition§2GPS系統(tǒng)組成TheGlobalPositioningSystemConstellationof24satellitesoperatedbytheU.S.DepartmentofDefenseOriginallyintendedformilitaryapplicationsbutextendedtocivilianuseEachsatellite’sorbitalperiodis12hours6satellitesvisibleineachhemisphere§2GPS系統(tǒng)組成GPSStructures

SpaceSegmentControlSegmentUserSegment§2GPS系統(tǒng)組成GPSStructures§2GPS系統(tǒng)組成GPSSpaceSegment§2GPS系統(tǒng)組成GPSSpaceSegment§2GPS系統(tǒng)組成GPSSpaceSegment§2GPS系統(tǒng)組成GPSSatellitesBLOCK-IBLOCK-II§2GPS系統(tǒng)組成GPSSatellitesBLOCK-IIRBLOCK-II§2GPS系統(tǒng)組成GPS系統(tǒng)衛(wèi)星的作用接收和儲(chǔ)存由地面注入站發(fā)送的導(dǎo)航電文和其他有關(guān)信息，并通過(guò)GPS信號(hào)形成電路，適時(shí)地發(fā)送給用戶；連續(xù)地向用戶發(fā)送導(dǎo)航定位信號(hào)，并通過(guò)導(dǎo)航電文報(bào)告自己的現(xiàn)勢(shì)位置、狀態(tài)和其他在軌衛(wèi)星的概略位置；接收并執(zhí)行地面主控站發(fā)送的衛(wèi)星調(diào)度命令，如適時(shí)地改正運(yùn)行偏差、調(diào)整衛(wèi)星姿態(tài)或者啟用備用時(shí)鐘等；衛(wèi)星上設(shè)有微處理機(jī)，進(jìn)行部分必要的數(shù)據(jù)處理工作；通過(guò)星載的高精度原子鐘提供精密的時(shí)間標(biāo)準(zhǔn)。鐘型時(shí)鐘頻率（Hz）每日穩(wěn)定度差1s所需時(shí)間石英鐘

5000000

109

30年銣鐘

6834682613

1012

30000年銫鐘

9192631770

1013

300000年氫鐘

1420405751

1015

30000000年§2GPS系統(tǒng)組成GPSControlSegment§2GPS系統(tǒng)組成GPSControlSegment§2GPS系統(tǒng)組成GPS地面監(jiān)控系統(tǒng)的作用根據(jù)本站和其他監(jiān)測(cè)站的觀測(cè)資料編制各衛(wèi)星的星歷、衛(wèi)星鐘差和大氣層的修正參數(shù)等，并把數(shù)據(jù)傳送到注入站；提供全球定位系統(tǒng)的時(shí)間基準(zhǔn)，各監(jiān)控站和GPS衛(wèi)星的原子鐘均應(yīng)與主控站的原子鐘同步或測(cè)出其間的鐘差，并把這些鐘差信息編入導(dǎo)航電文；對(duì)地面監(jiān)控系統(tǒng)的工作狀況及衛(wèi)星的健康狀況進(jìn)行診斷，調(diào)整偏離軌道的衛(wèi)星，使之沿預(yù)定軌道運(yùn)行；進(jìn)行衛(wèi)星調(diào)度，控制啟用備用衛(wèi)星以替代失效的工作衛(wèi)星?！?GPS系統(tǒng)組成GPSUserSegmentMilitary.Searchandrescue.Disasterrelief.Surveying.Marine,aeronauticalandterrestrialnavigation.Remotecontrolledvehicleandrobotguidance.Satellitepositioningandtracking.Shipping.GeographicInformationSystems(GIS).Recreation.§2GPS系統(tǒng)組成GPSUserSegment(Receiver)AshtechG8OEMGarmin

StreetPilotGarminGPSMap185WithSounder§2GPS系統(tǒng)組成GPSUserSegment(Receiver)Garmin

NavTalkTrimbleNT300DGarminVHF725§2GPS系統(tǒng)組成CompositionofGPSReceiver

GPS接收機(jī)主要由天線單元、主機(jī)單元和電源三部分組成。接收機(jī)主機(jī)由變頻器、信號(hào)通道、微處理器、存儲(chǔ)器及顯示模塊組成：§2GPS系統(tǒng)組成ClassificationofGPSReceiver1．按照用途分類（1）導(dǎo)航型接收機(jī)（2）測(cè)地型接收機(jī)（3）授時(shí)型接收機(jī)2．按照接收機(jī)的工作原理分類（1）碼相關(guān)型（CorrelationChannel）接收機(jī)（2）平方型（SquaringChannel）接收機(jī)（3）混合型（HybridChannel）接收機(jī)（4）碼相位型（CodePhaseChannel）接收機(jī)（5）干涉型（InterferometryChannel）接收機(jī)3．按照信號(hào)通道分類（1）多通道（Multi-Channel）接收機(jī)（2）序貫通道（SequencingChannel）接收機(jī)（3）多路復(fù)用通道（MultiplexingChannel）接收機(jī)4．根據(jù)接收的衛(wèi)星信號(hào)頻率分類（1）單頻（L1）接收機(jī)（2）雙頻（L1+L2）接收機(jī)?！?GPS系統(tǒng)組成§3GPS定位原理GPSPositioningTheory§3GPS定位原理PositionisBasedonTimeT+3Distancebetweensatelliteandreceiver=“3timesthespeedoflight”TSignalleavessatelliteattime“T”Signalispickedupbythereceiverattime“T+3”§3GPS定位原理PseudoRandomNoiseCodeReceiverPRNSatellitePRNTimeDifference§3GPS定位原理WhatTimeisitAnyway?ZuluTimeMilitaryTime

(localtimeona24hourclock)UniversalCoordinatedTimeGreenwichMeanTimeLocalTime:AMandPM(adjustedforlocaltimezone)GPSTime-13**GPSTimeiscurrentlyaheadofUTCby13seconds.§3GPS定位原理SignalFromOneSatelliteThereceiverissomewhereonthissphere.§3GPS定位原理SignalsFromTwoSatellites§3GPS定位原理ThreeSatellites(2DPositioning)§3GPS定位原理TriangulatingCorrectPosition§3GPS定位原理ThreeDimensional(3D)Positioning§3GPS定位原理FundamentalsofPositionFixingTherangebasedonmeasuringthetime-of-flightofaRFsignalthatleavesthetransmitteratt=t1andarrivesattheuseratt=t2isgivenby:Inthepresenceofaclockerror,dt(=b/c),therangeestimate(ormeasurement)becomes:§3GPS定位原理GPSPositionFixing§3GPS定位原理SV#1SV#2SV#3AsauserlocatedatpointX,thetruerangemeasurementstothethreeGPSsatellitesare:YourGPSreceiver,however,measuresr1,r2

andr3.Theserangemeasurementarecalledpseudoranges.GPSPseudoranges§3GPS定位原理SolvingNavigationEquationsSolvether-requationsEasyandgiveyouinsightintothelinearizationprocessGPSnavigationequations.The

r-rpositionfixingsystemofequationswherethreeindependentrangemeasurementsareavailablewasgivenas:§3GPS定位原理LinearizationbyExpansionExactEquationsyouwouldsolveinanidealworldEquationstheyoucanorwillsolve§3GPS定位原理LinearizationbyExpansion(2)(droppedhigherorderterms)Fortherangemeasurements,Forthepositioncoordinatex,Forthepositioncoordinatey,Where,§3GPS定位原理LinearizationbyExpansion(3)Takingthedifferencebetweenthetrueandestimatedvalues,Normallyyouhavemoreequationsthanunknowns.Thus,youcandoaleastsquaressolution.Thatis,§3GPS定位原理LinearizationbyExpansion(4)Becausewedon’thavetrueranges,butpseudo-ranges,weaugmenttheGmatrixwithacolumnofonesforthetimebias.Weneedatleast3measurementsforthe2-Dsolution.§3GPS定位原理LeastSquaresSolutionForthemoment,withoutproof,westatethattheleastsquaressolutionisgivenby,Algorithmforsolvingthenavigationequation:1)Pickaninitialguessforxandy2)Computeforasmanymeasurementsasyouhave3)Formforallmeasurementsandthenform4)Solvefor5)Updateyourinitialguessesforxandyasfollows:6)Repeatuntilconvergence§3GPS定位原理§4GPS信號(hào)與導(dǎo)航電文GPSSignalsandNavigationMessage§4

GPS信號(hào)與導(dǎo)航電文TheSignalsCarriersignalsL1andL2aremodulatedwithothersignals:Rangingcodes–binaryPRNCoarseacquisition(C/A)code-L1only1,023bitcodebroadcast@1.023Mbps,repeatseverymsEachsatellitehasitsownuniqueC/Acode.Precision(P)code–L1andL2AlsoaPRN,butis266dayslong@10.23Mbps–about2.35x10^14bitslong!DividedintoweeklongsegmentsandassignedtoeachsatelliteAlsousedforidentificationbutismoresecure,suitableformilitary.§4

GPS信號(hào)與導(dǎo)航電文TheSignalsReceiverscarryalistofidenticalcodesinorderto:Identifywhichsatellitethesignalisfromand,Asakindofruler,tomeasuretimedelayofsignal.Clocksmustbesynchronized§4

GPS信號(hào)與導(dǎo)航電文TheSignalsThenavigationmessageisalsomodulatedintobothcarriersignals37,500bitcode@50bpstakes750s–12andahalfminutesContainsvariousformsofinformationSatellitehealthstatusClockcorrectionsSatellitealmanac–predictedpositionsofsatellitesEphemeris–positionsofallsatellitesasafunctionoftime§4

GPS信號(hào)與導(dǎo)航電文TheWholeMessageTotalinformationbroadcast:Carriersignal-1575.42or1227.6MHzsinwaveNavigationmessageEphemerisdataprovidesthereceiverwiththeexactpositionsandtimesofall24satellitesatthetimeofbroadcastConstantlysynchronizesreceiver’squartzclockwithGPStimeC/AcodeandPcodeidentifyeachsatelliteandprovideastandardbywhichtomeasuretimedelay§4

GPS信號(hào)與導(dǎo)航電文FindingyourPositionThereceivermakesaroughestimate,apseudorangetoasatellitebyaligningtheC/AandPcodes.Usuallyaccuratetoafewhundredyards.EphemerisdatagivesexactlocationandtimeofthesatelliteatthebeginningofitstransmissionsCorrectionstoephemerissenttosatelliteshourlyQuartzclockinreceiverresynchronizesitselfwithGPStime,synchronizedwithin10nsReceiverhasallitneeds:locationsoffourormoresatellitesandthedistancetothem.3Dtrilaterationwillyieldanaccuratelocation§4

GPS信號(hào)與導(dǎo)航電文§5GPS系統(tǒng)誤差分析及補(bǔ)償GPSErrorandErrorMitigation§5GPS系統(tǒng)誤差分析及補(bǔ)償SourcesOfErrorGeometricDegreeofPrecision(GDOP)SelectiveAvailabilityDiscontinuedin5/1/2000AtmosphericEffectsIonosphericTroposphericMultipathEphemerisError (satellitepositiondata)SatelliteClockErrorReceiverClockError§5GPS系統(tǒng)誤差分析及補(bǔ)償

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AmountofErrorSatelliteclocks: 1.5to3.6metersOrbitalerrors: <1meterIonosphere: 5.0to7.0metersTroposphere: 0.5to0.7metersReceivernoise: 0.3to1.5metersMultipath: 0.6to1.2metersSelectiveAvailability (seenotes)Usererror: UptoakilometerormoreErrorsarecumulativeandincreasedbyPDOP.§5GPS系統(tǒng)誤差分析及補(bǔ)償GeometricDegreeofPrecision(GDOP)RelativegeometryofsatelliteconstellationtoreceiverWithfoursatellitesbestGDOPoccurswhenThreesatellitesjustabovethehorizonspacedevenlyaroundthecompassOnesatellitedirectlyoverheadSatelliteselectionminimizesGDOPerror§5GPS系統(tǒng)誤差分析及補(bǔ)償GoodGeometricDegreeofPrecision§5GPS系統(tǒng)誤差分析及補(bǔ)償BadGeometricDegreeofPrecision§5GPS系統(tǒng)誤差分析及補(bǔ)償ErrorMitigationTechniquesCarriersatL1andL2frequenciesIonosphericerrorisfrequencydependentsousingtwofrequencieshelpstolimiterrorDifferentialGPSPost-ProcessusermeasurementsusingmeasurederrorvaluesSpaceBasedAugmentationSystems(SBAS)ExamplesareU.S.WideAreaAugmentationSystem(WAAS),EuropeanGeostationaryNavigationalOverlayService(EGNOS)SBASprovidesatmospheric,ephemerisandsatelliteclockerrorcorrectionvaluesinrealtime?！?GPS系統(tǒng)誤差分析及補(bǔ)償DifferentialGPSUsesaGPSreceiveratafixed,surveyedlocationtomeasureerrorinpseudorangesignalsfromsatellitesPseudorangeerrorforeachsatelliteissubtractedfrommobilereceiverbeforecalculatingposition(typicallypostprocessed)§5GPS系統(tǒng)誤差分析及補(bǔ)償DifferentialGPS§5GPS系統(tǒng)誤差分析及補(bǔ)償GeostationaryWAASsatellitesGPSConstellationWAASControlStation(WestCoast)LocalAreaSystem(LAAS)WAASControlStation(EastCoast)WideAreaAugmentationSystem§5GPS系統(tǒng)誤差分析及補(bǔ)償+-

3meters+-15metersWithSelectiveAvailabilitysettozero,andunderidealconditions,aGPSreceiverwithoutWAAScanachievefifteenmeteraccuracymostofthetime.*UnderidealconditionsaWAASequippedGPSreceivercanachievethreemeteraccuracy95%ofthetime.**Precisiondependsongoodsatellitegeometry,openskyview,andnouserinducederrors.HowgoodisWAAS?§5GPS系統(tǒng)誤差分析及補(bǔ)償§6GPS應(yīng)用GPSApplications§6GPS應(yīng)用FourPrimaryFunctionsofGPSPositionandcoordinates.Thedistanceanddirectionbetweenanytwowaypoints,orapositionandawaypoint.Travelprogressreports.Accuratetimemeasurement.§6GPS應(yīng)用Applications–MilitaryMilitaryGPSuserequipmenthasbeenintegratedintofighters,bombers,tankers,helicopters,ships,submarines,tanks,jeeps,andsoldiers'equipment.Inadditiontobasicnavigationactivities,militaryapplicationsofGPSincludetargetdesignationofcruisemissilesandprecision-guidedweaponsandcloseairsupport.TopreventGPSinterceptionbytheenemy,thegovernmentcontrolsGPSreceiverexportsGPSsatellitesalsocancontainnucleardetonationdetectors.§6GPS應(yīng)用Applications–CivilianAutomobilesareoftenequippedGPSreceivers.Theyshowmovingmapsandinformationaboutyourpositiononthemap,speedyouaretraveling,buildings,highways,exitsetc.SomeofthemarketleadersinthistechnologyareGarminandTomTom,nottomentionthebuiltinGPSnavigationalsystemsfromautomotivemanufacturers.§6GPS應(yīng)用Applications–CivilianForaircraft,GPSprovidesContinuous,reliable,andaccuratepositioninginformationforallphasesofflightonaglobal