GPS全球定位系統(tǒng)的介紹的外文翻譯

1、譯文題目：IntroductiontotheGlobalPositioningSystem全球定位系統(tǒng)的介紹學(xué)生姓名：學(xué)號(hào)：專業(yè)：集成電路設(shè)計(jì)與集成系統(tǒng)IntroductiontotheGlobalPositioningSystemFrom"CorvallisMicrotechnology,Inc.1996”Chapter 1: :WhatisGPS?TheGlobalPositioningSystem(GPS)isalocationsystembasedonaconstellationofabout24satellitesorbitingtheearthataltitudesofa

2、pproximately11,000miles.GPSwasdevelopedbytheUnitedStatesDepartmentofDefense(DOD),foritstremendousapplicationasamilitarylocatingutility.TheDOD'sinvestmentinGPSisimmense.Billionsandbillionsofdollarshavebeeninvestedincreatingthistechnologyformilitaryuses.However,overthepastseveralyears,GPShasproven

3、tobeausefultoolinnon-militarymappingapplicationsaswell.GPSsatellitesareorbitedhighenoughtoavoidtheproblemsassociatedwithlandbasedsystems,yetcanprovideaccuratepositioning24hoursaday,anywhereintheworld.UncorrectedpositionsdeterminedfromGPSsatellitesignalsproduceaccuraciesintherangeof50to100meters.When

4、usingatechniquecalleddifferentialcorrection,userscangetpositionsaccuratetowithin5metersorless.Today,manyindustriesareleveragingofftheDOD'smassiveundertaking.AsGPSunitsarebecomingsmallerandlessexpensive,thereareanexpandingnumberofapplicationsforGPS.Intransportationapplications,GPSassistspilotsand

5、driversinpinpointingtheirlocationsandavoidingcollisions.FarmerscanuseGPStoguideequipmentandcontrolaccuratedistributionoffertilizersandotherchemicals.Also，GPSisusedforprovidingaccuratelocationsandasanavigationtoolforhikers,huntersandboaters.ManywouldarguethatGPShasfounditsgreatestutilityinthefieldofG

6、eographicInformationSystems(GIS).Withsomeconsiderationforerror,GPScanprovideanypointonearthwithauniqueaddress(itspreciselocation).AGISisbasicallyadescriptivedatabaseoftheearth(oraspecificpartoftheearth).GPStellsyouthatyouareatpointX,Y,ZwhileGIStellsyouthatX,Y,Zisanoaktree,oraspotinastreamwithapHleve

7、lof5.4.GPStellsusthe"where".GIStellsusthe"what".GPS/GISisreshapingthewaywelocate,organize,analyzeandmapourresources.Chapter 2: :Trilateration-HowGPSDeterminesaLocationInanutshell,GPSisbasedonsatelliteranging-calculatingthedistancesbetweenthereceiverandthepositionof3ormoresatellit

8、es(4ormoreifelevationisdesired)andthenapplyingsomegoodoldmathematics.Assumingthepositionsofthesatellitesareknown,thelocationofthereceivercanbecalculatedbydeterminingthedistancefromeachofthesatellitestothereceiver.GPStakesthese3ormoreknownreferencesandmeasureddistancesand"triangulates"anadd

9、itionalposition.Asanexample,assumethatIhaveaskedyoutofindmeatastationarypositionbaseduponafewclueswhichIamwillingtogiveyou.First,ItellyouthatIamexactly10milesawayfromyourhouse.YouwouldknowIamsomewhereontheperimeterofaspherethathasanoriginasyourhouseandaradiusof10miles.Withthisinformationalone,youwou

10、ldhaveadifficulttimetofindmesincethereareaninfinitenumberoflocationsontheperimeterofthatsphere.Second,ItellyouthatIamalsoexactly12milesawayfromtheABCGroceryStore.Nowyoucandefineasecondspherewithitsoriginatthestoreandaradiusof12miles.YouknowthatIamlocatedsomewhereinthespacewheretheperimetersofthesetw

11、ospheresintersect-buttherearestillmanypossibilitiestodefinemylocation.Addingadditionalsphereswillfurtherreducethenumberofpossiblelocations.Infact,athirdoriginanddistance(Itellyouam8milesawayfromtheCityClock)narrowsmypositiondowntojust2points.Byaddingonemoresphere,youcanpinpointmyexactlocation.Actual

12、ly,the4thspheremaynotbenecessary.Oneofthepossibilitiesmaynotmakesense,andthereforecanbeeliminated.Forexample,ifyouknowIamabovesealevel,youcanrejectapointthathasnegativeelevation.Mathematicsandcomputersallowustodeterminethecorrectpointwithonly3satellites.Basedonthisexample,youcanseethatyouneedtoknowt

13、hefollowinginformationinordertocomputeyourposition:A) Whatisthepreciselocationofthreeormoreknownpoints(GPSsatellites)?B) WhatisthedistancebetweentheknownpointsandthepositionoftheGPSreceiver?Chapter 3: ee:HowtheCurrentLocationsofGPSSatellitesareDeterminedGPSsatellitesareorbitingtheEarthatanaltitudeof

14、11,000miles.TheDODcanpredictthepathsofthesatellitesvs.timewithgreataccuracy.Furthermore,thesatellitescanbeperiodicallyadjustedbyhugeland-basedradarsystems.Therefore,theorbits,andthusthelocationsofthesatellites,areknowninadvance.Today'sGPSreceiversstorethisorbitinformationforalloftheGPSsatellites

15、inwhatisknownasanalmanac.Thinkofthealmanacasa"busschedule"advisingyouofwhereeachsatellitewillbeataparticulartime.EachGPSsatellitecontinuallybroadcaststhealmanac.YourGPSreceiverwillautomaticallycollectthisinformationandstoreitforfuturereference.TheDepartmentofDefenseconstantlymonitorstheorb

16、itofthesatelliteslookingfordeviationsfrompredictedvalues.Anydeviations(causedbynaturalatmosphericphenomenonsuchasgravity),areknownasephemeriserrors.Whenephemeriserrorsaredeterminedtoexistforasatellite,theerrorsaresentbackuptothatsatellite,whichinturnbroadcaststheerrorsaspartofthestandardmessage,supp

17、lyingthisinformationtotheGPSreceivers.Byusingtheinformationfromthealmanacinconjuctionwiththeephemeriserrordata,thepositionofaGPSsatellitecanbeverypreciselydeterminedforagiventime.Chapter 4: r:ComputingtheDistanceBetweenYourPositionandtheGPSSatellitesGPSdeterminesdistancebetweenaGPSsatelliteandaGPSre

18、ceiverbymeasuringtheamountoftimeittakesaradiosignal(theGPSsignal)totravelfromthesatellitetothereceiver.Radiowavestravelatthespeedoflight,whichisabout186,000milespersecond.So,iftheamountoftimeittakesforthesignaltotravelfromthesatellitetothereceiverisknown,thedistancefromthesatellitetothereceiver(dist

19、ance=speedxtime)canbedetermined.Iftheexacttimewhenthesignalwastransmittedandtheexacttimewhenitwasreceivedareknown,thesignal'straveltimecanbedetermined.Inordertodothis,thesatellitesandthereceiversuseveryaccurateclockswhicharesynchronizedsothattheygeneratethesamecodeatexactlythesametime.Thecoderec

20、eivedfromthesatellitecanbecomparedwiththecodegeneratedbythereceiver.Bycomparingthecodes,thetimedifferencebetweenwhenthesatellitegeneratedthecodeandwhenthereceivergeneratedthecodecanbedetermined.Thisintervalisthetraveltimeofthecode.Multiplyingthistraveltime,inseconds,by186,000milespersecondgivesthedi

21、stancefromthereceiverpositiontothesatelliteinmiles.Chapter 5: e:Four(4)Satellitestogivea3DpositionInthepreviousexample,yousawthatittookonly3measurementsto"triangulate"a3Dposition.However,GPSneedsa4thsatellitetoprovidea3Dposition.Why?Threemeasurementscanbeusedtolocateapoint,assumingtheGPSre

22、ceiverandsatelliteclocksarepreciselyandcontinuallysynchronized,therebyallowingthedistancecalculationstobeaccuratelydetermined.Unfortunately,itisimpossibletosynchronizethesetwoclocks,sincetheclocksinGPSreceiversarenotasaccurateastheverypreciseandexpensiveatomicclocksinthesatellites.TheGPSsignalstrave

23、lfromthesatellitetothereceiververyfast,soifthetwoclocksareoffbyonlyasmallfraction,thedeterminedpositiondatamaybeconsiderablydistorted.Theatomicclocksaboardthesatellitesmaintaintheirtimetoaveryhighdegreeofaccuracy.However,therewillalwaysbeaslightvariationinclockratesfromsatellitetosatellite.Closemoni

24、toringoftheclockofeachsatellitefromthegroundpermitsthecontrolstationtoinsertamessageinthesignalofeachsatellitewhichpreciselydescribesthedriftrateofthatsatellite'sclock.TheinsertionofthedriftrateeffectivelysynchronizesalloftheGPSsatelliteclocks.ThesameprocedurecannotbeappliedtotheclockinaGPSrecei

25、ver.Therefore,afourthvariable(inadditiontox,yandz),time,mustbedeterminedinordertocalculateapreciselocation.Mathematically,tosolveforfourunknowns(x,y,z,andt),theremustbefourequations.IndeterminingGPSpositions,thefourequationsarerepresentedbysignalsfromfourdifferentsatellites.Chapter 6: :TheGPSErrorBu

26、dgetTheGPSsystemhasbeendesignedtobeasnearlyaccurateaspossible.However,therearestillerrors.Addedtogether,theseerrorscancauseadeviationo+f/-50-100metersfromtheactualGPSreceiverposition.Thereareseveralsourcesfortheseerrors,themostsignificantofwhicharediscussedbelow:AtmosphericConditionsTheionosphereand

27、tropospherebothrefracttheGPSsignals.ThiscausesthespeedoftheGPSsignalintheionosphereandtropospheretobedifferentfromthespeedoftheGPSsignalinspace.Therefore,thedistancecalculatedfrom"SignalSpeedxTime"willbedifferentfortheportionoftheGPSsignalpaththatpassesthroughtheionosphereandtroposphereand

28、fortheportionthatpassesthroughspace.Asmentionedearlier,GPSsignalscontaininformationaboutephemeris(orbitalposition)errors,andabouttherateofclockdriftforthebroadcastingsatellite.Thedataconcerningephemeriserrorsmaynotexactlymodelthetruesatellitemotionortheexactrateofclockdrift.Distortionofthesignalbyme

29、asurementnoisecanfurtherincreasepositionalerror.Thedisparityinephemerisdatacanintroduce1-5metersofpositionalerror,clockdriftdisparitycanintroduce0-1.5metersofpositionalerrorandmeasurementnoisecanintroduce0-10metersofpositionalerror.EphemeriserrorsshouldnotbeconfusedwithSelectiveAvailability(SA),whic

30、histheintentionalalterationofthetimeandephemerissignalbytheDepartmentofDefense.AGPSsignalbouncingoffareflectivesurfacepriortoreachingtheGPSreceiverantennaisreferredtoasmultipath.Becauseitisdifficulttocompletelycorrectmultipatherror,eveninhighprecisionGPSunits,multipatherrorisaseriousconcerntotheGPSu

31、ser.Chapter 7: en:MeasuringGPSAccuracyAsdiscussedabove,thereareseveralexternalsourceswhichintroduceerrorsintoaGPSposition.Whiletheerrorsdiscussedabovealwaysaffectaccuracy,anothermajorfactorindeterminingpositionalaccuracyisthealignment,orgeometry,ofthegroupofsatellites(constellation)fromwhichsignalsa

32、rebeingreceived.Thegeometryoftheconstellationisevaluatedforseveralfactors,allofwhichfallintothecategoryofDilutionOfPrecision,orDOP.DOPisanindicatorofthequalityofthegeometryofthesatelliteconstellation.Yourcomputedpositioncanvarydependingonwhichsatellitesyouuseforthemeasurement.Differentsatellitegeome

33、triescanmagnifyorlessentheerrorsintheerrorbudgetdescribedabove.AgreateranglebetweenthesatelliteslowerstheDOP,andprovidesabettermeasurement.AhigherDOPindicatespoorsatellitegeometry,andaninferiormeasurementconfiguration.SomeGPSreceiverscananalyzethepositionsofthesatellitesavailable,baseduponthealmanac

34、,andchoosethosesatelliteswiththebestgeometryinordertomaketheDOPaslowaspossible.AnotherimportantGPSreceiverfeatureistobeabletoignoreoreliminateGPSreadingswithDOPvaluesthatexceeduser-definedlimits.OtherGPSreceiversmayhavetheabilitytouseallofthesatellitesinview,thusminimizingtheDOPasmuchaspossible.全球定位

35、系統(tǒng)的介紹摘自CorvallisMicrotechnology公司，1996第一章：什么是GPS？全球定位系統(tǒng)（GPS）是一種基于24顆高度大約11000英里的地球軌道衛(wèi)星的定位系統(tǒng)。GPS是美國(guó)國(guó)防部（DOD）因?yàn)槠湓谲娛露ㄎ谎b置方面巨大的應(yīng)用而開(kāi)發(fā)的。國(guó)防部對(duì)GPS的投入是極大的。已經(jīng)有數(shù)十億美元的投資為了開(kāi)發(fā)這種軍事應(yīng)用技術(shù)。然而，過(guò)去一段時(shí)間以來(lái)，GPS已經(jīng)被證實(shí)是在測(cè)繪非軍事地圖應(yīng)用方面十分有用的工具。GPSfi星的軌道足夠高以避免以土地為基礎(chǔ)的系統(tǒng)相關(guān)的問(wèn)題，還可以在世界上任何地方提供每天24小時(shí)準(zhǔn)確的定位。在裸眼可視位置GPSE星信號(hào)產(chǎn)生的定位精度為50到100米。當(dāng)使用差分技術(shù)

36、時(shí)，用戶可以得到精度為5米以下的定位。今天，許多行業(yè)都促使國(guó)防部改變。由于GPSI位正變得更小，更便宜，GPS的應(yīng)用正在不斷增加。在交通運(yùn)輸應(yīng)用方面，GPSB助飛行員和司機(jī)準(zhǔn)確定位它們的位置，避免碰撞。農(nóng)民可以使用GPS8I導(dǎo)設(shè)備并且控制化肥和其他化學(xué)品的準(zhǔn)確分布。止匕外，GPSffl于提供準(zhǔn)確的位置，并作為徒步旅行者，獵人和船民的導(dǎo)航工具。很多人認(rèn)為，GPS已經(jīng)在地理信息系統(tǒng)（GIS）領(lǐng)域發(fā)揮最大的應(yīng)用。在考慮到一些誤差的情況下，GPSM以提供地球上任何一點(diǎn)的唯個(gè)地址（它的精確位置）。GIS從根本上說(shuō)是地球的一個(gè)描述的數(shù)據(jù)庫(kù)（或地球的特定部分）。GP8告訴你，你是在點(diǎn)X,Y,Z,而GIS告訴

37、彳KX,Y,Z點(diǎn)是一棵橡樹(shù)，或河流中的一個(gè)pH值5.4的點(diǎn)。GPS告訴我們，“在哪里”，GIS告訴我們“是什么”。GPS/GIS正在重塑定位，管理，分析，并且映射我們的資源。第二章：三邊定位一一GPS是怎樣定位的簡(jiǎn)單地說(shuō)，GPSg基于衛(wèi)星測(cè)距-計(jì)算接收器和3顆或更多顆衛(wèi)星（4個(gè)或更多，如果需要高程）之間的距離，然后用一些以前的正確數(shù)字進(jìn)行計(jì)算。假設(shè)衛(wèi)星的位置是已知的，通過(guò)確定每個(gè)衛(wèi)星到接收機(jī)的距離，可以計(jì)算出接收機(jī)的位置。GPS用這3個(gè)或更多的已知的參考和測(cè)量距離然后“三角測(cè)量”出額外的位置。作為一個(gè)例子，假設(shè)我要你根據(jù)我給你提供的很少的一些線索讓你在一個(gè)固定的位置找到我。首先，我告訴你，我離

38、你的房子正好是10英里遠(yuǎn)。你會(huì)知道我在一個(gè)以你的房子為圓心，半徑10英里的球形邊界的地方。只有這些信息，你很難找到我，因?yàn)樵谶@球形的邊界上有無(wú)數(shù)的位置點(diǎn)。第二，我告訴你，我也正好離ABC雜貨店12英里遠(yuǎn)。現(xiàn)在，你可以畫出一個(gè)以雜貨店為圓心，半徑12英里的球形。你知道，我所在的地方，在兩個(gè)球形空間的周長(zhǎng)交叉的地方-但我的位置還是有很多的可能性。添加更多的范圍將進(jìn)一步減少可能的地點(diǎn)。事實(shí)上，第三個(gè)圓心和距離（我告訴你是8英里遠(yuǎn)的城市時(shí)鐘）使我的位置縮小到只有2點(diǎn)。再增加一個(gè)范圍，你可以找出我的確切位置。其實(shí)，第四球體可能不是必需的。其中一個(gè)可能是沒(méi)有意義的，并因此可以被消除。例如，如果你知道我是海

39、平面上，你可以拒絕一個(gè)海拔為負(fù)的點(diǎn)。數(shù)學(xué)和計(jì)算機(jī)讓我們能夠只用3顆衛(wèi)星確定正確的點(diǎn)。基于這個(gè)例子，你可以明白，你需要知道以下信息，以便計(jì)算你的位置：A）3個(gè)或更多的已知點(diǎn)（GPSS星）的精確位置是什么?B）已知點(diǎn)白位置和GPSR收器之間是多少距離?第三章：如何確定GPS衛(wèi)星當(dāng)前位置GPSE星在高度為11000公里的軌道繞地球飛行。國(guó)防部可以非常準(zhǔn)確地預(yù)測(cè)衛(wèi)星的路徑與時(shí)間的關(guān)系。此外，衛(wèi)星還可以定期通過(guò)巨大的陸基雷達(dá)系統(tǒng)進(jìn)行調(diào)整。因此，軌道，衛(wèi)星的位置，都是預(yù)先已知的。今天的GPS8收器存儲(chǔ)所有的GPS衛(wèi)星的軌道信息，被稱為星歷。你的星歷像“巴士時(shí)刻表"，提醒你每顆衛(wèi)星在一個(gè)特定的時(shí)間

40、點(diǎn)在什么地方。每個(gè)GPS1星不斷廣播星歷。你的GPS接收器會(huì)自動(dòng)收集這些信息，并將其存儲(chǔ)以供將來(lái)參考。國(guó)防部不斷地監(jiān)視衛(wèi)星的軌道預(yù)測(cè)值的偏差。任何偏差（由于自然的大氣現(xiàn)象，如重力），被稱為星歷誤差。當(dāng)被確定為存在衛(wèi)星星歷誤差，誤差被發(fā)送備份到該衛(wèi)星，依次將錯(cuò)誤作為標(biāo)準(zhǔn)的消息的一部分廣播，提供這種信息給GPS接收機(jī)。通過(guò)使用星歷表的信息誤差數(shù)據(jù)，可以很精確地在一個(gè)給定的時(shí)間確定GPS衛(wèi)星的位置。第四章：計(jì)算你的位置和GPS1星之間的距離GPS!過(guò)測(cè)量衛(wèi)星和接收機(jī)之間無(wú)線電信號(hào)（GPSJ號(hào)）傳輸所花費(fèi)的時(shí)間來(lái)確定衛(wèi)星和接收機(jī)的距離。無(wú)線電波以光速傳播，這是大約每秒186,000英里的速度。因此，如果信號(hào)從衛(wèi)星到接收機(jī)的時(shí)間量是已知的，衛(wèi)星到接收機(jī)的距離（距離=4度時(shí)間）可以被確定。如果信號(hào)發(fā)送和收到的時(shí)間確定，信號(hào)的傳輸時(shí)間才能確定。為了做到這一點(diǎn)，衛(wèi)星和接收機(jī)使用非常精確的同步時(shí)鐘，以便它們?cè)谕耆嗤臅r(shí)間，生成相同的代碼。從衛(wèi)星接收的代碼可以跟接收器產(chǎn)生的代碼進(jìn)行比較。通過(guò)比較代碼，衛(wèi)星產(chǎn)生代碼時(shí)與接收機(jī)接收后產(chǎn)生代碼之間的時(shí)間差可以被確定。這個(gè)時(shí)間間隔為代碼的旅行時(shí)間。每秒186,000英里的速度乘以這個(gè)時(shí)間間隔就是接收機(jī)位置與衛(wèi)星之間的距離第五章：四顆衛(wèi)星定位3D位置在前面的例子中，你看到了，只用了3個(gè)測(cè)量“三角測(cè)量”三維