User's Manual

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D.Glossary

N72GNSSReferenceReceiverUserGuidePage65

three‐dimensionalmeasurements.OtherDOPvaluesincludeVDOP(verticalDOP)

andHDOP(HorizontalDilutionofPrecision).

UsingamaximumPDOPvalueisidealforsituationswherebothverticaland

horizontalprecisionareimportant.

postprocessing Postprocessingistheprocessingofsatellitedataafter

ithasbeencollected,in

ordertoeliminateerror.Thisinvolvesusingcomputersoftwaretocomparedata

fromtheroverwithdatacollectedatthebasestation.

real‐time

differential

GPS

Alsoknownasreal‐timedifferentialcorrectionorDGPS.Real‐timedifferentialGPS

istheprocessofcorr ectingGPS

dataasyoucollectit.Correctionsarecalculatedat

abasestationandthensenttothereceiverthrougharadiolink.Astherover

receivesthepositionitappliesthecorrectionstogiveyouaveryaccurateposition

inthefield.

Mostreal‐timedifferentialcorrectionmethodsapplycorrections

tocodephase

positions.RTKusescarrierphasemeasurements.

WhileDGPSisagenericterm,itscommoninterpretationisthatitentailstheuse

ofsingle‐frequencycodephasedatasentfromaGPSbasestationtoaroverGPS

receivertoprovidesub‐meterpositionaccuracy.Theroverreceivercan

beata

longrange(greaterthan100km(62miles))fromthebasestation.

referencestation Seebasestation

rover AroverisanymobileGPSreceiverthatisusedtocollectorupdatedatainthe

field,typicallyatanunknownlocation.

RTCM RadioTechnicalCommissionforMaritime

Services.Acommissionestablishedto

defineadifferentialdatalinkforthereal‐timedifferentialcorrectionofrovingGPS

receivers.TherearethreeversionsofRTCMcorrectionmessages.AllCHCGPS

receiversuseVersion2protocolforsingle‐frequencyDGPStypecorrections.

CarrierphasecorrectionsareavailableonVersion2,or

onthenewerVersion3

RTCMprotocol,whichisavailableoncertainCHCdual‐frequencyreceivers.The

Version3RTCMprotocolismorecompactbutisnotaswidelysupportedas

Version2.

RTK Real‐timekinematic.Areal‐timedifferentialGPSmethodthatusescarrierphase

measurementsforgreater

accuracy.

SBAS Satellite‐BasedAugmentationSystem.SBASisbasedondifferentialGPS,but

appliestowidearea(WAAS/EGNOSandMSAS)networksofreferencestations.

Correctionsandadditionalinformationarebr oadcastviageostationarysatellites.

signal‐to‐noise

ratio

SNR.Thesignalstrengthofasatelliteisameasureoftheinformationcontent

of

thesignal,relativetothesignal’snoise.ThetypicalSNRofasatelliteat30°

elevationisbetween47and50dBHz.ThequalityofaGPSpositionisdegradedif

theSNRofoneormoresatellitesintheconstellationfallsbelow39.

skyplot Thesatelliteskyplotconfirms

receptionofadifferentiallycorrectedGPSsignaland

displaysthenumberofsatellitestrackedbytheGPSreceiver,aswellastheir

relativepositions.

SNR Seesignal‐to‐noiseratio

UTC UniversalTimeCoordinated.Atimestandardbasedonlocalsolarmeantimeat

theGreenwichmeridian.

VRS VirtualReferenceStation.

AVRSsystemconsistsofGNSShardware,software,and