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毕业设计（论文）外文文献翻译文献、资料中文题目：全球定位系统（GPS）文献、资料英文题目：GlobalPositioningSystem(GPS)文献、资料来源：文献、资料发表（出版）日期：院（部）：专业：班级：姓名：学号：指导教师：翻译日期：2017.02.14GlobalPositioningSystem(GPS)DonaldPfostandWilliamCasady,ExtensionAgriculturalEngineersKentShannon,AssociateDirectoroftheMissouriPrecisionAgricultureCenterUniversityofMissouri-ColumbiaRangedeterminationfactorsEachGPSsatellitecontinuouslybroadcaststworadiosignalsonseparateL-bandfrequencies(theL-bandisfrom1,000to2,000MHz).TheL1signal(transmittedat1575.42MHz)carriestwocodes,aCoarse/Acquisition(C/A)codeandaPrecision(P)code.TheL2signal(transmittedat1227.60MHz)carriesonlythePcode,whichisencryptedsoonlythemilitaryandother“authorized”receiverscaninterpretit.TheuseofboththeL1andL2signalsandtheirPcodesproduceswhatiscalledthePrecisePositioningService(PPS)andisavailabletotheU.S.andalliedmilitary,U.S.governmentagenciesandauthorizedcivilianusers.ThesystemavailableforallcivilianuseaccessesonlytheL1signalandtheC/AcodeandisknownastheStandardPositioningService.GPStechnologyGlobalPositioningSystem(GPS)receiversprovideamethodfordetermininglocationanywhereontheearth.Accurate,automatedpositiontrackingwithGPSreceiversallowsfarmersandagriculturalserviceproviderstoautomaticallyrecorddataandapplyvariableratesofinputstosmallerareaswithinlargerfieldsAGPSreceivercanbecomparedwithasimpleAMorFMradio.AGPSreceiver“listens”forthesignalsthatarebroadcastfromthesatellitesoftheUnitedStatesDepartmentofDefense(DOD)GlobalPositioningSystem.Orbitingaroundtheearthatanaltitudeof12,550miles,thesesatellitesareinpredictablelocations;hence,werefertothesystemofsatellitesastheGPSconstellation.Eachsatellitebroadcastsalmanacinformationcontainingthepositionofallsatellitesintheconstellation.GPSreceiversusethealmanactodeterminethepositionofthesatellites.Minorvariationsintheorbitsofthesatellitesoccurduetogravitationalforcesfromthesunandthemoon.TheDODcontinuouslymonitorsthesatellitesandadjuststhealmanacinformationtorepresenttheactualorbitsofthesatellites.ThebroadcastsignalsalsocontainapreciselytimedpredictablecodethataGPSreceivercanusetodeter-minehowlongthesignalrequiredtoreachthereceiver.AmicroprocessorwithinaGPSreceiverusesthesedelaysandthepositionofthesatellitetocalculatethedistancetoeachsatellite,andthenusesthisinformationtodeterminelocationthroughtriangulation.Triangulationisamathematicalmethodforlocatingpointsonaplaneinthree-dimensionalspace.Ifthedistancestoeachofthreesatellitesandyourapproximatelocationontheearthareknown,theGPSreceivercancalculateitsterrestrialposition.Ifinformationfromfoursatellitesisavailable,elevationcanalsobedetermined.AccuracyTheaccuracyobtainedgenerallydependsonfivefactors1)properinstallation2)thedegreeoftechnologyusedinthereceiver3)thenumberandlocationofsatellites4)errorsintroducedbyselectiveavailability(SA),atmosphericconditions,thetroposphere,theionosphere,andmultipathing一radiosignalsbouncingoffobjectsinthearea5)differentialcorrections.InstallationGPSantennasshouldbemountedonthecenterlineofacombine,tractorortruckandaboveanypartofthemachinerythatmightobstructalineofsighttoasatellite.Ifthecabiscenteredandthetopofthecabisaboveotherportionsofthemachine,acab-topmountingmaybethebestlocation.However,onasteepsideslope,ahighmountingpointwillresultinanerrorinpositioncalculationduetotheoffsetinhorizontalposition.GPSandDGPSreceiversmayhaveseparateantennasbutusuallytherewillbeacombinationantennasothatbotharecenteredatthesamelocation.Adelayofseveralsecondsoftenoccursinagriculturalapplicationssuchasyieldmonitoring,sprayingandfertilizerapplication.Example:Iftheantennaonasprayertraveling10mphismounted30ftaheadoftheboomsandaratechangeatthecontrolleriseffectedattheboomtwosecondslater,theratechangewilloccurwhentheboomsreachthelocationoftheantennawherethechangewasmade.Atanyothergroundspeed,theratechangeattheboomswillnotoccuratthesamelocationasthecontroller.Atimeadjustmentmustusuallybefactoredintothesystemtocompensatefortimedelaysinsensingorproductapplication.Electricalinterferencecanresultfromelectricalstorms,powerlines,2-wayradios,nearbyradiotransmitters,electricmotors,microwavetowers,cellularphones,vehicularelectricalequipmentsuchasalternatorsandignitionsystemsonspark-ignitionenginesandothersources.Changingthepositionoftheantennaoraddingnoisesuppressionkitsmayreduceinterferenceproblemsfromalternatorsandignitionsystems.FollowtheinstructionsforinstallationoftheGPSequipment,makingsurethatallconnectionsaretight.TechnologyLow-costreceiversreceivesignalsfromonesatelliteatatimeandrequiremoretimetodeterminethelocationthanareceivercapableofreceivingfoursignalssimultaneously.Usually,sevento10satellitesareinviewatanyonetimeandmoresophisticatedreceiverswillproducethemostaccuratelocation.Reacquisitiontimeisthetimeittakestogetanaccuratepositionfixafterashort-timelossofsatellitesignals;thismayoccurforavarietyofreasons,includingtravelingneartreesorbuildingsandlosingthe‘lineofsight’tosatellites.Reacquisitiontimeisimportantformostagriculturalapplicationsandespeciallyforguidancewithapplicatorsandaircraft.NewtechnologyinGPSreceivershasshorte