外文翻譯--全球衛(wèi)星定位系統(tǒng).doc

-1-本科畢業(yè)論文外文文獻及譯文文獻、資料題目：GlobalPositioningSystem文獻、資料來源：/wiki/Global_Positioning_System文獻、資料發(fā)表（出版）日期：2009.01.03院（部）：土木工程學院專業(yè)：土木工程班級：姓名：學號：指導教師：翻譯日期：外文文獻：-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