GPS全球定位系统的介绍的外文翻译

译文题目：IntroductiontotheGlobalPositioningSystem全球定位系统的介绍学生姓名：学号：专业：集成电路设计与集成系统IntroductiontotheGlobalPositioningSystem---------From“CorvallisMicrotechnology,Inc.1996”ChapterOne:WhatisGPS?TheGlobalPositioningSystem(GPS)isalocationsystembasedonaconstellationofabout24satellitesorbitingtheearthataltitudesofapproximately11,000miles.GPSwasdevelopedbytheUnitedStatesDepartmentofDefense(DOD),foritstremendousapplicationasamilitarylocatingutility.TheDOD'sinvestmentinGPSisimmense.Billionsandbillionsofdollarshavebeeninvestedincreatingthistechnologyformilitaryuses.However,overthepastseveralyears,GPShasproventobeausefultoolinnon-militarymappingapplicationsaswell.GPSsatellitesareorbitedhighenoughtoavoidtheproblemsassociatedwithlandbasedsystems,yetcanprovideaccuratepositioning24hoursaday,anywhereintheworld.UncorrectedpositionsdeterminedfromGPSsatellitesignalsproduceaccuraciesintherangeof50to100meters.Whenusingatechniquecalleddifferentialcorrection,userscangetpositionsaccuratetowithin5metersorless.Today,manyindustriesareleveragingofftheDOD'smassiveundertaking.AsGPSunitsarebecomingsmallerandlessexpensive,thereareanexpandingnumberofapplicationsforGPS.Intransportationapplications,GPSassistspilotsanddriversinpinpointingtheirlocationsandavoidingcollisions.FarmerscanuseGPStoguideequipmentandcontrolaccuratedistributionoffertilizersandotherchemicals.Also，GPSisusedforprovidingaccuratelocationsandasanavigationtoolforhikers,huntersandboaters.ManywouldarguethatGPShasfounditsgreatestutilityinthefieldofGeographicInformationSystems(GIS).Withsomeconsiderationforerror,GPScanprovideanypointonearthwithauniqueaddress(itspreciselocation).AGISisbasicallyadescriptivedatabaseoftheearth(oraspecificpartoftheearth).GPStellsyouthatyouareatpointX,Y,ZwhileGIStellsyouthatX,Y,Zisanoaktree,oraspotinastreamwithapHlevelof5.4.GPStellsusthewhere.GIStellsusthewhat.GPS/GISisreshapingthewaywelocate,organize,analyzeandmapourresources.ChapterTwo:Trilateration-HowGPSDeterminesaLocationInanutshell,GPSisbasedonsatelliteranging-calculatingthedistancesbetweenthereceiverandthepositionof3ormoresatellites(4ormoreifelevationisdesired)andthenapplyingsomegoodoldmathematics.Assumingthepositionsofthesatellitesareknown,thelocationofthereceivercanbecalculatedbydeterminingthedistancefromeachofthesatellitestothereceiver.GPStakesthese3ormoreknownreferencesandmeasureddistancesandtriangulatesanadditionalposition.Asanexample,assumethatIhaveaskedyoutofindmeatastationarypositionbaseduponafewclueswhichIamwillingtogiveyou.First,ItellyouthatIamexactly10milesawayfromyourhouse.YouwouldknowIamsomewhereontheperimeterofaspherethathasanoriginasyourhouseandaradiusof10miles.Withthisinformationalone,youwouldhaveadifficulttimetofindmesincethereareaninfinitenumberoflocationsontheperimeterofthatsphere.Second,ItellyouthatIamalsoexactly12milesawayfromtheABCGroceryStore.Nowyoucandefineasecondspherewithitsoriginatthestoreandaradiusof12miles.YouknowthatIamlocatedsomewhereinthespacewheretheperimetersofthesetwospheresintersect-buttherearestillmanypossibilitiestodefinemylocation.Addingadditionalsphereswillfurtherreducethenumberofpossiblelocations.Infact,athirdoriginanddistance(Itellyouam8milesawayfromtheCityClock)narrowsmypositiondowntojust2points.Byaddingonemoresphere,youcanpinpointmyexactlocation.Actually,the4thspheremaynotbenecessary.Oneofthepossibilitiesmaynotmakesense,andthereforecanbeeliminated.Forexample,ifyouknowIamabovesealevel,youcanrejectapointthathasnegativeelevation.Mathematicsandcomputersallowustodeterminethecorrectpointwithonly3satellites.Basedonthisexample,youcanseethatyouneedtoknowthefollowinginformationinordertocomputeyourposition:A)Whatisthepreciselocationofthreeormoreknownpoints(GPSsatellites)?B)WhatisthedistancebetweentheknownpointsandthepositionoftheGPSreceiver?ChapterThree:HowtheCurrentLocationsofGPSSatellitesareDeterminedGPSsatellitesareorbitingtheEarthatanaltitudeof11,000miles.TheDODcanpredictthepathsofthesatellitesvs.timewithgreataccuracy.Furthermore,thesatellitescanbeperiodicallyadjustedbyhugeland-basedradarsystems.Therefore,theorbits,andthusthelocationsofthesatellites,areknowninadvance.Today'sGPSreceiversstorethisorbitinformationforalloftheGPSsatellitesinwhatisknownasanalmanac.Thinkofthealmanacasabusscheduleadvisingyouofwhereeachsatellitewillbeataparticulartime.EachGPSsatellitecontinuallybroadcaststhealmanac.YourGPSreceiverwillautomaticallycollectthisinformationandstoreitforfuturereference.TheDepartmentofDefenseconstantlymonitorstheorbitofthesatelliteslookingfordeviationsfrompredictedvalues.Anydeviations(causedbynaturalatmosphericphenomenonsuchasgravity),areknownasephemeriserrors.Whenephemeriserrorsaredeterminedtoexistforasatellite,theerrorsaresentbackuptothatsatellite,whichinturnbroadcaststheerrorsaspartofthestandardmessage,supplyingthisinformationtotheGPSreceivers.Byusingtheinformationfromthealmanacinconjuctionwiththeephemeriserrordata,thepositionofaGPSsatellitecanbeverypreciselydeterminedforagiventime.ChapterFour:ComputingtheDistanceBetweenYourPositionandtheGPSSatellitesGPSdetermine