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THE GLOBAL POSITIONING SYSTEM AND ITS USAGE IN …

Areasfromsurveyingto constructionto ;why it was started,thecompo-nents of thesystem,how it is utilized,andhow thesystemis expectedtochangeover addition,thispaper willdiscusstheoptimalpointsto take measurements to maximizee doneby determininghow to maintainthepathlengthof theshape witha minimumnumber of beenmany signi cant technologicaladvancesover thelast fty years,oneof which is theGlobalPositioningSystem(GPS).TheGloba lPositioningSys-temis a satellitenavigationsystemthatallowsusers to invented,theprimarymethodof navigationrevolvedaroundthemapandcompass ,butthatis notso , technologyhasadvancedin thetimesinceGPSwas rstinventedtogive recent years,GPShasbeenusedformorethansimplenav igationalexercisesincludingapplicationsi n geology, agriculture,land-scaping,construction, thisway, GPSis usedto measuredistancesacrosslargeareassuchas ,this

of the Global Positioning System, then explains how measurements are taken using GPS and how GPS is applied to real situations, and ends with a short discussion on …

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Transcription of THE GLOBAL POSITIONING SYSTEM AND ITS USAGE IN …

1 Areasfromsurveyingto constructionto ;why it was started,thecompo-nents of thesystem,how it is utilized,andhow thesystemis expectedtochangeover addition,thispaper willdiscusstheoptimalpointsto take measurements to maximizee doneby determininghow to maintainthepathlengthof theshape witha minimumnumber of beenmany signi cant technologicaladvancesover thelast fty years,oneof which is theGlobalPositioningSystem(GPS).TheGloba lPositioningSys-temis a satellitenavigationsystemthatallowsusers to invented,theprimarymethodof navigationrevolvedaroundthemapandcompass ,butthatis notso , technologyhasadvancedin thetimesinceGPSwas rstinventedtogive recent years,GPShasbeenusedformorethansimplenav igationalexercisesincludingapplicationsi n geology, agriculture,land-scaping,construction, thisway, GPSis usedto measuredistancesacrosslargeareassuchas ,thisnewtechnologyis notperfect.

2 It willexploresomeof thesedrawbacks,witha is usuallymoreaccurate,or at leastmoree cient, to measurelargedistancesusingGPS,thereis stillsomeerrorinvolvedin themeasurement whichresultsfromtheerrorof willbe discussedin Section2, butsometimesit is notpossibleto willbe important to incorporatetheerrorintothemeasurements anddeterminethee ectof thiserror(thelattersectionsof thispaper willdojustthat).Additionally, GPSis notthemoste cient method ofmeasuringshortdistances(ontheorderof a classroomor house)becauseGPSis notthataccurateyet,butis e cient whenmeasuringdistancesacrosscam-pusoronl argerareasof property.

3 InformationregardingtheGlobalPosition-in gSystemanditsapplicationsin thispaper is primarilyfromthreebooks;In-troductiontoG PS:TheGlobalPositioningSystemby AhmedEl-Rabbany [1],GlobalPositioningSystem:TheoryandPra cticeby BernardHofmann-Wellenhof12 MATT OLMSTEADandHerbertLichtenegger[2], andGPSforLandSurveyorsby JanVan-Sickle[3].Thispaper is dividedinto rstsectioncontainsthediscus-sionof GPSandhow it discussiononthehistoryof theGlobalPositioningSystem,thenexplainsh ow measurements aretaken usingGPSandhow GPSis appliedto realsituations,andendswitha thepaper lookat howto estimateerrorin pathmeasurements andhow to bestapproximatepathlengthsusinga nitenumber of broken into parts,withthe rstpartintroducingthebar-bell conceptof errorapproximation,thenextpartusingtheba r-bell conceptto measurea triangularpathwhileassumingerroron themeasurements.

4 Andthelastpartof thissectionestimatingtheperimeterof a to estimatethepathlengthof othershapes by takinginto account curvature,pathlengthtravelled, nalsectionof thispaper discussesunsolved problemsandfuturedirectionsto take whilelookingat thesuccessorto developedby JohnHopkinsAppliedPhysicsLaboratoryin 1959andde-claredoperationalin 1962when ve satelliteswerein operatedby give coordinatesto ,in 1967civilianusebecameallowed,andTRANSITi s stillin usetoday by thesmallnumber of satelliteswhich causestimegapsin measurements as thesatellitespassoverheadat low navigationalaccuracy.

5 In1973theUSAirForcesetforthto developtheGlobalPositioningSystemto improve thesede use,President ReaganandCongressdirectedtheDepartment of Defenseto promotecivilianuseof GPSando erit freeof chargeaftera Sovietshootingof a KoreanAirlinerin 1993,theSecretaryof DefensedeclaredInitialOperationalCapabil ity of GPS,whichmeansthatit is nolongera developmentalsystem.[2] :ConfigurationTheGlobalPositioningSystem is setupto ensurecontinuousworldwidecoveragewhich it managesto doby havingthesatellitesarrangedin sixorbitalplaneswithat leastfoursatellitesin each each planeinorderto attainworldwidecoverage,butit is even betterwithfouror moresatellitesin each orbitalplane.

6 [1]Therearethreesegments to theGPS:thespacesegment, controlsegment, consistsof the24satelliteconstellation,witheach of thesatellitestransmittinga signaldownto signalcontains vecomponents,two carrierfrequencies,two digitalcodes,anda usedtodeterminethedistancefromthereceive r tothesatellite,andthenavigationmessagein cludesthelocationof thesatelliteasafunctionof is madeupof a worldwidenetworkof trackingstationswiththemastercontrolstat ionin ColoradoSprings, {BASEDPATH LENGTHESTIMATES3segment is responsiblefortrackingthesatellitesto predictfuturesatellitelocationsandalsoto makes surethesatelliteis functioningcorrectly.}

7 Theusersegmentincludesallof theusersof GPS,bothcivilianandmilitary, whoareableto usereceiversin orderto ndtheirpositiononearth.[1]A GPSsatellite(Figure1) ableto generateabout700wattsof power andmoves at about8700milesper three-dimensionalstabilizationto make of theearthandthereareon-boardbatteriesto providepower thermostaticallycontrolledheatersandre ective insulationso theycanstay attheappropriatetemperatureto ensurethattheoscillators(clock) a facility at Cape Canaveral,FLpriortolaunch to make suretheyarefunctioningproperly.[3] a pictureof a Block II [1]GPSstartedwith11 Block I rstsatellitewas launchedon Febru-ary22,1978andthelastBlock I satellitewas launchedonOctober 9, satelliteswereusedprimarilyforexperiment alpurposeswitha lifeexpectancyof I satellitescameBlock II/IIAsatelliteswhich canfunc-tionwithoutgroundsupportfor14or 180days,respectively.

8 A totalof 28 BlockII/IIAsatelliteshave beenlaunchedandincludenewsecurity featuressuch as se-lective availability andantispoo II/IIAsatelliteshave a lifetimeof ,butalmostallof IIRsatellites4 MATT OLMSTEAD arecurrentlybeinglaunched,areexpectedto have a higheraccuracy, andareex-pectedto be ableto goat least180days withoutgroundcorrectionsor accuracydegradation.[1] Thecurrent con gurationof satellitesin theskyis 5 Block II, 18 Block IIA,and6 Block IIRfora totalof 29satellites.[4]Thecontrolsegment consistsof themastercontrolstation(MCS),monitorsta- tions, ve monitorstationsareinColoradoSprings,Hawa ii,Kwajalein(anislandwestof Hawaii),DiegoGarcia(anislandsouthof Indiaandnortheastof Madagascar,andAscensionIsland(anislandin betweenSouthAmericaandAfrica,eastof Brazil),andtheirlocationsareknownprecise ly.)

9 Thesemonitorstationsareresponsiblefortra ckingallof theGPSsatel-litesin viewandthreeof themhave groundantennasso thatinformationcanbeuploadedto of thesemonitorstationsandgroundcon-trolsta tions(nottheMCS)is unmannedandoperatedremotelyfromtheMCS.[1 ]Thereareseveraladditionalsatellitenavig ationsystemscreatedandoperatedby systemcalledGLONASS which is 21op-erationalsatellitesand3 sparesatellitesthatorbitat ,taking11hoursand15minutesto orbit,andarearrangedin L-bandcarriers,a C/Acode onL1,P-code onbothL1andL2,anda erenceis thateach GLONASS satellitehasitsownfrequencybutthisisgoin gto changeso thereis onlyonefrequency, makingGLONASS even moresim-ilarto determinewhich satelliteis January1996.

10 GLONASSwas completedwith24workingsatellitesbutin May newgenerationof satellitesareexpectedto be launchedandfeatureimproved clocks andcapability of is possibleto usebothGPSandGLONASS together,butGLONASS usesPZ-90whereasGPSusesWGS84as as much as a 20 meterdi erence.[1]Chinahaslaunchedtwo navigationsatellitesthatareplacedin geostationaryorbitsat about36000 Kmabove Earth' now thissystemis usedinlandandmarinetransportationandChin ais planningto builda secondpositioningandnavigationsystemwith moresatellitesandmorecoverage.[1]GLONASS andGPSarenotableto meetallof thecivilaviationrequirementsandareaugmen tedby GLONASS withgeostationarysatelliteswithnavigatio ntranspondersandgroundreferencestations.


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