无人机专业英语 课件 13 Chap4 Satellite Navigation-How does the GPS work

EnglishforUnmannedaerialvehicle无人机专业英语第三部分第四部分区域卫星导航系统全球卫星导航系统Unit4Satellitenavigation——GNSS、Regionalnavigationsatellitesystems、HowdoestheGPSwork?第五部分GPS工作原理Satnav=satellite['sætəlaɪt]navigation[nævɪ'geɪʃ(ə)n]卫星导航geo-spatial[dʒi:əʊˈspeɪʃəl]地理空间Longitude['lɒn(d)ʒɪtju:d]经度latitude['lætɪtju:d]纬度Transmit[trænz'mɪt]传输Satellite['sætəlaɪt]tracking['trækɪŋ]卫星追踪Synchronisation[sɪnŋkrənaɪ'zeʃən]同步GNSS=globalnavigationsatellitesystem全球导航卫星系统MEO=medium['miːdɪəm]Earthorbit

['ɔːbɪt]中地球轨道NewWords&PhrasesOrbital['ɔ:bɪt(ə)l]inclination[ɪnklɪ'neɪʃ(ə)n]轨道倾角SBAS=SatelliteBasedAugmentationSystems星基增强系统GBAS=GroundBasedAugmentationSystems地基增强系统WAAS=WideAreaAugmentationSystem广域增强系统EGNOS=EuropeanGeostationary[dʒiːə(ʊ)'steɪʃ(ə)n(ə)rɪ]NavigationOverlay[əʊvə'leɪ]Service欧洲同步卫星导航覆盖服务MSAS=Multi-FunctionalSatelliteAugmentationSystem多功能卫星增强系统LAAS=

LocalAreaAugmentationSystem

局域增强系统NewWords&PhrasesSpectrum['spektrəm]光谱DGPS=Differential[,dɪfə'renʃ(ə)l]GPS差分GPSRTK=RealTimeKinematic[,kɪnɪ'mætɪk]实时动态terrestrial

[tə'restrɪəl]陆地的Deviate['di:vɪeɪt]偏离Ephemeris[ɪ'fem(ə)rɪs]星历表(记录卫星运行参数)Atomic[ə'tɒmɪk]clock原子钟Trilateration[,trailætə'reiʃən]三边测量/三球交汇Ionosphere[aɪ'ɒnəsfɪə]电离层NewWords&PhrasesTangent[ˈtændʒənt]切线Radionavigation[,reɪdɪəʊ,nævɪ'ɡeɪʃən]无线电导航

compatible[kəm'pætɪb(ə)l]兼容的CBOC=Composite['kɒmpəzɪt]Binary['baɪnərɪ]Offset['ɒfset]Carrier

['kærɪə]

复合二进制偏移载波GEO=Geostationary[dʒiːə(ʊ)'steɪʃ(ə)n(ə)rɪ]orbit['ɔ:bɪt]对地静止轨道GSO=Geosynchronous[,dʒiːə(ʊ)'sɪŋkrənəs]orbit地球同步轨道Military['mɪlɪt(ə)rɪ]军事的Sensitivity[sensɪ'tɪvɪtɪ]敏感性NewWords&Phrasespseudo-random['sjuːdəʊ,'rændəm]code伪随机码UHF=Ultra['ʌltrə]HighFrequency超高频Plastic['plæstɪk]塑料的Troposphere['trɒpə(ʊ)sfɪə]对流层NewWords&PhrasesGPSTheUnitedStates'GlobalPositioningSystem(GPS)consistsofupto32

mediumEarthorbit

satellitesinsixdifferent

orbitalplanes,withtheexactnumberofsatellitesvaryingasoldersatellitesareretiredandreplaced.Operationalsince1978andgloballyavailablesince1994,GPSiscurrentlytheworld'smostusedsatellitenavigationsystem.Part3GlobalnavigationsatellitesystemsGLONASSTheformerly

Soviet,andnow

Russian,

GlobalNavigationSatelliteSystem,orGLONASS,isaspace-basedsatellitenavigationsystemthatprovidesacivilianradionavigation-satelliteserviceandisalsousedbytheRussianAerospaceDefenceForces.Thefullorbitalconstellationof24GLONASSsatellitesenablesfullglobalcoverage.Part3GlobalnavigationsatellitesystemsGalileoThe

EuropeanUnion

and

EuropeanSpaceAgency

agreedinMarch2002tointroducetheirownalternativetoGPS,calledthe

Galileopositioningsystem.Galileobecameoperationalon15December2016(globalEarlyOperationalCapability(EOC))

AtanestimatedcostofEUR3.0billion,thesystemof30

MEO

satelliteswasoriginallyscheduledtobeoperationalin2010.Theoriginalyeartobecomeoperationalwas2014.

Thefirstexperimentalsatellitewaslaunchedon28December2005.

Part3GlobalnavigationsatellitesystemsGalileoGalileoisexpectedtobecompatiblewiththe

modernizedGPS

system.ThereceiverswillbeabletocombinethesignalsfrombothGalileoandGPSsatellitestogreatlyincreasetheaccuracyofposition.Galileoisexpectedtobeinfullservicein2020andatasubstantiallyhighercost.ThemainmodulationusedinGalileoOpenServicesignalisthe

CompositeBinaryOffsetCarrier

(CBOC)modulation.伽利略开放业务信号的主要调制方式是复合二进制偏移载波(CBOC)调制。Part3GlobalnavigationsatellitesystemsBeiDou-2China

hasindicatedtheyplantocompletetheentiresecondgenerationBeiDouNavigationSatelliteSystem(BDSorBeiDou-2,formerlyknownasCOMPASS),byexpandingcurrentregional(Asia-Pacific)serviceintoglobalcoverageby2020.TheBeiDou-2systemisproposedtoconsistof30

MEO

satellitesandfivegeostationarysatellites.A16-satelliteregionalversion(coveringAsiaandPacificarea)wascompletedbyDecember2012.Part3GlobalnavigationsatellitesystemsBeiDou-1Chineseregional(Asia-Pacific,16satellites)networktobeexpandedintothewholeBeiDou-2globalsystemwhichconsistsofall35satellitesby2020.中国区域(亚太，16颗卫星)网络将扩展到整个北斗-2全球系统，到2020年由35颗卫星组成。Part4RegionalnavigationsatellitesystemsNAVICThe

NAVIC

or

NavigationwithIndianConstellation

isanautonomousregionalsatellitenavigationsystemdevelopedby

IndianSpaceResearchOrganisation

(ISRO)whichwouldbeunderthetotalcontrolof

Indiangovernment.ThegovernmentapprovedtheprojectinMay2006,withtheintentionofthesystemcompletedandimplementedon28April2016.Itwillconsistofaconstellationof7navigationalsatellites.

3ofthesatelliteswillbeplacedinthe

Geostationaryorbit(GEO)

andtheremaining4inthe

Geosynchronousorbit(GSO)

tohavealargersignalfootprintandlowernumberofsatellitestomaptheregion.Part4RegionalnavigationsatellitesystemsNAVICItisintendedtoprovideanall-weatherabsolutepositionaccuracyofbetterthan7.6metersthroughout

India

andwithinaregionextendingapproximately1,500

kmaroundit.

它的目的是在整个印度及其周围约1500公里的区域，全天候绝对定位精度超过7.6米。印度完整的目标已说明控制，空间段、地面段和用户接收器都是在印度建造的。AgoalofcompleteIndiancontrolhasbeenstated,withthe

spacesegment,

groundsegment

anduserreceiversallbeingbuiltinIndia.Part4RegionalnavigationsatellitesystemsQZSSTheQuasi-ZenithSatelliteSystem(QZSS),isaproposedthree-satelliteregional

timetransfer

systemandenhancementfor

GPS

covering

Japan.ThefirstdemonstrationsatellitewaslaunchedinSeptember2010.Part4RegionalnavigationsatellitesystemsTheSatelliteNetworkTheGPSsatellitestransmitsignalstoaGPSreceiver.Thesereceiverspassivelyreceivesatellitesignals;theydonottransmit.GPSreceiversrequireanunobstructedviewofthesky,sotheycanonlybeusedeffectivelyoutdoors.EarlyreceiversdidnotperformwellwithinforestedareasorneartallbuildingsbutlaterreceiverdesignssuchasSiRFStarIII,MTKetchaveovercomethisandimprovedperformanceandsensitivitymarkedly.GPSoperationsdependonaveryaccuratetimereference,whichisprovidedbyatomicclocksonboardthesatellites.Part5GPS—Howitworks？TheSatelliteNetworkEachGPSsatellitetransmitsdatathatindicatesitslocationandthecurrenttime.AllGPSsatellitessynchronizeoperationssothattheserepeatingsignalsaretransmittedatthesameinstant.Thesignals,movingatthespeedoflight,arriveataGPSreceiveratslightlydifferenttimesbecausesomesatellitesarefurtherawaythanothers.Part5GPS—Howitworks？TheSatelliteNetworkAstheFig3-1shows,thedistancetotheGPSsatellitescanbedeterminedbyestimatingtheamountoftimeittakesfortheirsignalstoreachthereceiver.WhenthereceiverestimatesthedistancetoatleastfourGPSsatellites,asitcancalculateitspositioninthreedimensions.Part5GPS—Howitworks？Fig.3-1SignalsfrommultiplesatellitesTheSatelliteNetworkOnceithasinformationonhowfarawayatleastthreesatellitesare,yourGPSreceivercanpinpointyourlocationusingaprocesscalledtrilateration(seetheFig.3-2).Part5GPS—Howitworks？Fig.3-2trilaterationTheSatelliteNetworkImagineyouarestandingsomewhereonEarthwiththreesatellitesintheskyaboveyou.IfyouknowhowfarawayyouarefromsatelliteA,thenyouknowyoumustbelocatedsomewhereontheredcircle.IfyoudothesameforsatellitesBandC,youcancalculatedyourlocationbyseeingwherethethreecirclesintersect.ThisisjustwhatyourGPSreceiverdoes,althoughitusesoverlappingspheresratherthancircles.Part5GPS—Howitworks？TheSatelliteNetworkThemoresatellitesthereareabovethehorizonthemoreaccuratelyyourGPSunitcandeterminewhereyouare.地平线上的卫星越多，你的全球定位系统就越能准确地确定你在哪里。Part5GPS—Howitworks？TheSatelliteNetworkAsshowninFig3-3,thereareatleast24operationalGPSsatellitesatalltimesplusanumberofspares.

Thesatellites,operatedbytheUSDOD,orbitwithaperiodof12hours(twoorbitsperday)ataheightofabout11,500milestravelingat9000mph(3.9km/sor14,000kph).Groundstationsareusedtopreciselytrackeachsatellite'sorbit.Part5GPS—Howitworks？Fig.3-3TheNavstarGPSConstellation如图3-3所示，在任何时候至少有24颗可运行的GPS卫星及其备件。这些卫星由美国国防部运行，运行周期为12小时(每天两次)。在大约11，500英里的高度以每小时9000英里(3.9公里/秒或14，000公里/小时)的速度行驶。地面站用于精确跟踪每颗卫星的轨道。Part5GPS—Howitworks？HowPositionisDeterminedAGPSreceiver"knows"thelocationofthesatellitesbecausethatinformationisincludedinthetransmitted

Ephemerisdata.Byestimatinghowfarawayasatellite

is,thereceiveralso"knows"itislocatedsomewhereonthesurfaceofanimaginaryspherecentredatthesatellite.GPS接收机“知道”卫星的位置，因为该信息包含在发送星历数据中。通过估计一颗卫星的距离，接收器也“知道”它是位于以卫星为中心的假想球体表面的某个地方。Itthendeterminesthesizesofseveralspheres,oneforeachsatelliteandthereforeknowsthereceiverislocatedwherethesespheresintersect.Part5GPS—Howitworks？GPSAccuracyTheaccuracyofapositiondeterminedwithGPSdependsonthetypeofreceiver.MostconsumerGPSunitshaveanaccuracyofaboutplusorminus10m.OthertypesofreceiversuseamethodcalledDifferentialGPS(DGPS)toobtainmuchhigheraccuracy.DGPSrequiresanadditionalreceiverfixedataknownlocationnearby.Observationsmadebythestationaryreceiverareusedtocorrectpositionsrecordedbytherovingunits,producinganaccuracygreaterthan1meter.固定接收器所作的观测用于校正流动单元所记录的位置，从而产生大于1米的精度。Part5GPS—Howitworks？HowIsTheSignalTimed?AllGPSsatelliteshaveseveralatomicclocks.Thesignalthatissentoutisarandomsequence,eachpartofwhichisdifferentfromeveryother,calledpseudo-randomcode.Thisrandomsequenceisrepeatedcontinuously.所有的GPS卫星都有几个原子钟。发出的信号是随机序列，每个部分都不同，称为伪随机码。这个随机序列是持续更新的。Part5GPS—Howitworks？HowIsTheSignalTimed?AllGPSreceiversknowthissequenceandrepeatitinternally.Therefore,satellitesandthereceiversmustbeinsynch.Thereceiverpicksupthesatellite'stransmissionandcomparestheincomingsignaltoitsowninternalsignal.Bycomparinghowmuchthesatellitesignalislagging,thetraveltimebecomesknown.所有GPS接收机都知道这个序列，并在内部重复。因此，卫星和接收器必须同步。接收机接收卫星的传输，并将接收到的信号与自己的内部信号进行比较。通过比较卫星信号的滞后程度，就知道了传输时间。Part5GPS—Howitworks？Whatdoesthesignalconsistof?GPSsatellitestransmittworadiosignals.ThesearedesignatedasL1andL2.ACivilianGPSusestheL1signalfrequency(1575.42MHz)intheUHFband.Thesignalstravelbylineofsight,meaningtheywillpassthroughclouds,glass,plasticetcbutwillnottravelthroughsolidobjectssuchasbuildingsandmountains.全球定位系统卫星发射两个无线电信号。它们被命名为L1和L2。民用全球定位系统在超高频波段使用L1信号频率(1575.42兆赫)。这些信号是通过直线传播的，能够穿过云，玻璃，塑料等，但不会穿越实体物体，如建筑物和山脉。Part5GPS—Howitworks？Whatdoesthesignalconsistof?TheGPSsignalcontainsthreedifferentbitsofinformation—apseudorandomcode,almanacdataandephemerisdata.The

pseudorandomcode

issimplyanI.D.codethatidentifieswhichsatelliteistransmittinginformation.YoucanoftenviewthisnumberonyourGPSunit'ssatelliteinformationpage,thenumberattachedtoeachsignalbaridentifieswhichsatellitesit'sreceivingasignalfrom.Part5GPS—Howitworks？Whatdoesthesignalconsistof?Almanacdata

isdatathatdescribestheorbitalcoursesofthesatellites.Everysatellitewillbroadcastalmanacdataforeverysatellite.YourGPSreceiverusesthisdatatodeterminewhichsatellitesitexpectstoseeinthelocalsky.Itcanthendeterminewhichsatellitesitshouldtrack.WithAlmanacdatathereceivercanconcentrateonthosesatellitesitcanseeandforgetaboutthosethatwouldbeoverthehorizonandoutofview.Almanacdataisnotpreciseandcanbevalidformanymonths.Part5GPS—Howitworks？Whatdoesthesignalconsistof?Ephemerisdata

isdatathattellstheGPSreceiverwhereeachGPSsatelliteshouldbeatanytimethroughouttheday.Eachsatellitewillbroadcastitsownephemerisdatashowingtheorbitalinformationforthatsatelliteonly.星历数据是一种数据，它告诉GPS接收机每颗GPS卫星应该在一天中的时间信息。每颗卫星都会广播自己的星历表，显示该卫星的轨道信息。Part5GPS—Howitworks？Whatdoesthesignalconsistof?Becauseephemerisdataisverypreciseorbitalandclockcorrectiondatanecessaryforprecisepositioning,itsvalidityismuchshorter.Itisbroadcastinsixsecondblocksrepeatedevery30seconds.由于星历数据是精密定位所必需的轨道和时钟校正数据，其有效性要短得多。它播放一帧需6秒，重复周期为30秒。Thedataisconsideredvalidforupto4hoursbutdifferentmanufacturersconsideritvalidfordifferentperiodswithsometreatingitasstaleafteronly2hours.Part5GPS—Howitworks？SourcesofGPSsignalerrorFactorsthatcandegradetheGPSsignalandthusaffectaccuracyincludethefollowing:1)Ionosphereandtropospheredelays—Thesatellitesignalslowsasitpassesthroughtheatmosphere.TheGPSsystemusesabuilt-inmodelthatcalculatesanaverageamountofdelaytopartiallycorrectforthistypeoferror.2)Signalmultipath—ThisoccurswhentheGPSsignalisreflectedoffobjectssuchastallbuildingsorlargerocksurfacesbeforeitreachest