User's Manual

N72GNSSReferenceReceiverUserGuidePage63
D. GLOSSARY
basestation Alsocalledreferencestation.Abasestationinconstruction,isareceiverplacedat
aknownpointonajobsit ethattracksthesamesatellitesasanRTKrover,and
providesareal‐timedifferentialcorrectionmessagestreamthroughradiotothe
rover,toobtaincentimeterlevelpositionson
acontinuousreal‐timebasis.Abase
stationcanalsobeapartofavirtualreferencestationnetwork,oralocationat
whichGPSobservationsarecollectedoveraperiodoftime,forsubsequent
postprocessingtoobtainthemostaccuratepositionforthelocation.
carrier Aradiowavehaving
atleastonecharacteristic(suchasfrequency,amplitude,or
phase)thatcanbevariedfromaknownreferencevaluebymodulation.
carrierfrequency Thefrequencyoftheunmodulatedfundamentaloutputofaradiotransmitter.The
GPSL1carrierfrequencyis1575.42MHz.
carrierphase ThetimetakenfortheL1or
L2carriersignalgeneratedbythesatellitetoreach
theGPSreceiver.Measuringthenumberofcarrierwavesbetweenthesatellite
andreceiverisaveryaccuratemethodofcalculatingthedistancebetweenthem.
CMR
CMR+
CompactMeasurementRecord.Areal‐timemessageformatdevelopedbyTrimble
forbroadcastingcorrections
tootherTrimblemainboardreceivers.CMRisamore
efficientalternativetoRTCM.
DGPS Seereal‐timedifferentialGPS.
differential
correction
DifferentialcorrectionistheprocessofcorrectingGPSdatacollectedonarover
withdatacollectedsimultaneouslyatabasestation.Becausethebasestationis
onaknownlocation,
anyerrorsindatacollectedatthebasestationcanbe
measured,andthenecessarycorrectionsappliedtotheroverdata.
Differentialcorrectioncanbedoneinreal‐time,orafterthedatahasbeen
collectedbypostprocessing.
DifferentialGPS Seereal‐timedifferentialGPS.
DOP DilutionofPrecision.A
measureofthequalityofGPSpositions,basedonthe
geometryofthesatellitesusedtocomputethepositions.Whensatellitesare
widelyspacedrelativetoeachother,theDOPvalueislower,andpositionaccuracy
isgreater.Whensatellitesareclosetogetherinthesky,theDOPishigherand
GPS
positionsmaycontainagreaterlev eloferror.
PDOP(PositionDOP)indicat esthethree‐dimensionalgeometryofthesatellites.
OtherDOPvaluesincludeHDOP(HorizontalDOP)andVDOP(VerticalDOP),which
indicatetheaccuracyofhorizontalme asurements(latitudeandlongitude)and
verticalmeasurementsrespectively.PDOPisrelatedtoHDOP
andVDOPas
follows:
PDOP²=HDOP²+VDOP²
dual‐frequency
GPS
AtypeofreceiverthatusesbothL1andL2signalsfromGPSsatellites.A
dual‐frequencyreceivercancomputemoreprecisepositionfixesoverlonger
distancesandundermoreadverseconditionsbecauseitcompensatesfor
ionosphericdelays.
EGNOS
 EuropeanGeostationaryNavigationOverlayService.Asatellite‐based
augmentationsystem(SBAS)thatprovidesafree‐to‐airdifferentialcorrection
serviceforGPS.
EGNOSistheEuropeanequivalentofWAAS,whichisavailableintheUnited