外文翻译--全球卫星定位系统.doc

-1-本科毕业论文外文文献及译文文献、资料题目：GlobalPositioningSystem文献、资料来源：/wiki/Global_Positioning_System文献、资料发表（出版）日期：2009.01.03院（部）：土木工程学院专业：土木工程班级：姓名：学号：指导教师：翻译日期：外文文献：-2-GlobalPositioningSystemTheGlobalPositioningSystem(GPS)isaglobalnavigationsatellitesystem(GNSS)developedbytheUnitedStatesDepartmentofDefenseandmanagedbytheUnitedStatesAirForce50thSpaceWing.ItistheonlyfullyfunctionalGNSSintheworld,canbeusedfreely,andisoftenusedbyciviliansfornavigationpurposes.TheGlobalPositioningSystem(GPS)isasatellite-basednavigationsystemmadeupofanetworkof24satellitesplacedintoorbitbytheU.S.DepartmentofDefense.GPSwasoriginallyintendedformilitaryapplications,butinthe1980s,thegovernmentmadethesystemavailableforcivilianuse.GPSworksinanyweatherconditions,anywhereintheworld,24hoursaday.TherearenosubscriptionfeesorsetupchargestouseGPS.Itusesaconstellationofbetween24and32mediumEarthorbitsatellitesthattransmitpreciseradiowavesignals,whichallowGPSreceiverstodeterminetheircurrentlocation,thetime,andtheirvelocity.ItsofficialnameisNAVSTARGPS.AlthoughNAVSTARisnotanacronym,1afewbackronymshavebeencreatedforit.Sinceitbecamefullyoperationalin1993,GPShasbecomeawidelyusedaidtonavigationworldwide,andausefultoolformap-making,landsurveying,commerce,scientificuses,andhobbiessuchasgeocaching.Also,theprecisetimereferenceisusedinmanyapplicationsincludingthescientificstudyofearthquakesandasarequiredtimesynchronizationmethodforcellularnetworkprotocolssuchastheIS-95standardforCDMA.GPSsatellitescircletheearthtwiceadayinaverypreciseorbitandtransmitsignalinformationtoearth.GPSreceiverstakethisinformationandusetriangulationtocalculatetheusersexactlocation.Essentially,theGPSreceivercomparesthetimeasignalwastransmittedbyasatellitewiththetimeitwasreceived.ThetimedifferencetellstheGPSreceiverhowfarawaythesatelliteis.Now,withdistancemeasurementsfromafewmoresatellites,thereceivercandeterminetheuserspositionanddisplayitontheunitselectronicmap.AGPSreceivermustbelockedontothesignalofatleastthreesatellitestocalculatea2Dposition(latitudeandlongitude)andtrackmovement.Withfourormoresatellitesinview,thereceivercandeterminetheusers3Dposition(latitude,longitudeandaltitude).Oncetheuserspositionhasbeendetermined,theGPSunitcancalculateotherinformation,suchasspeed,bearing,track,tripdistance,distancetodestination,sunriseandsunsettimeandmore.-3-HistoryThefirstsatellitenavigationsystem,Transit,usedbytheUnitedStatesNavy,wasfirstsuccessfullytestedin1960.Usingaconstellationoffivesatellites,itcouldprovideanavigationalfixapproximatelyonceperhour.In1967,theU.S.NavydevelopedtheTimationsatellitewhichprovedtheabilitytoplaceaccurateclocksinspace,atechnologythatGPSreliesupon.Inthe1970s,theground-basedOmegaNavigationSystem,basedonsignalphasecomparison,becamethefirstworldwideradionavigationsystem.ThedesignofGPSisbasedpartlyonsimilarground-basedradionavigationsystems,suchasLORANandtheDeccaNavigatordevelopedintheearly1940s,andusedduringWorldWarII.AdditionalinspirationfortheGPScamewhentheSovietUnionlaunchedthefirstman-madesatellite,Sputnikin1957.AteamofU.S.scientistsledbyDr.RichardB.KershnerweremonitoringSputniksradiotransmissions.Theydiscoveredthat,becauseoftheDopplereffect,thefrequencyofthesignalbeingtransmittedbySputnikwashigherasthesatelliteapproached,andlowerasitcontinuedawayfromthem.Theyrealizedthatsincetheyknewtheirexactlocationontheglobe,theycouldpinpointwherethesatellitewasalongitsorbitbymeasuringtheDopplerdistortion.AfterKoreanAirLinesFlight007wasshotdownin1983afterstrayingintotheUSSRsprohibitedairspace,3PresidentRonaldReaganissuedadirectivemakingGPSfreelyavailableforcivilianuseasacommongood.4Thesatelliteswerelaunchedbetween1989and1993.Initiallythehighestqualitysignalwasreservedformilitaryuse,whilethesignalavailableforcivilianusewasintentionallydegraded(SelectiveAvailability,SA).SelectiveAvailabilitywas-4-endedin2000,improvingtheprecisionofcivilianGPSfromabout100mtoabout20m.OfcrucialimportanceforthefunctionofGPSistheplacementofatomicclocksinthesatellites,firstproposedbyFriedwardtWinterbergin1955.5Onlythencantherequiredpositionaccuracybereached.TimelineIn1972,theUSAirForceCentralInertialGuidanceTestFacility(HollomanAFB)conducteddevelopmentalflighttestsoftwoprototypeGPSreceiversoverWh