Garmin C330 - Page 16

Personal Navigation System: Garmin C330
Matthew Kimball – Retail Sales Trainer - Simulation Exercise
Garmin C330 FG (PANEL)v1.0 16 of 16
WhatisWAAS:
You'veheardthetermWAAS,seenitonpackagingandadsforGarmin®products,andmaybeeven
knowitstandsforWideAreaAugmentationSystem.Okay,sowhattheheckisit?Basically,it'sasystem
ofsatellitesandgroundstationsthatprovideGPSsignalcorrections,givingyouevenbetterposition

accuracy.Howmuchbetter?Tryanaverageofuptofivetimesbetter.AWAAS‐capablereceivercangive
youapositionaccuracyofbetterthanthreemeters95percent ofthetime.Andyoudon'thaveto
purchaseadditionalreceivingequipmentorpayservicefeestoutilizeWAAS.

TheoriginsofWAAS
TheFederalAviationAdministration(FAA)andtheDepartmentofTransportation(DOT)aredeveloping
theWAASprogramforuseinprecisionflightapproaches.Currently,GPSalonedoesnotmeettheFAA's
navigationrequirementsforaccuracy,integrity,andavailability.WAAScorrectsforGPSsignalerrors
causedbyionosphericdisturbances,timing,andsatelliteorbit
errors,anditprovidesvitalintegrity
informationregardingthehealthofeachGPSsatellite.

HowitWorks
WAASconsistsofapproximately25groundreferencestationspositionedacrosstheUnitedStatesthat
monitorGPSsatellitedata.Twomasterstations,locatedoneithercoast,collectdatafromthereference
stationsandcreateaGPScorrectionmessage.ThiscorrectionaccountsforGPSsatelliteorbitandclock
driftplussignaldelayscaused
bytheatmosphereandionosphere.Thecorrecteddifferentialmessageis
thenbroadcastthroughoneoftwogeostationarysatellites,orsatelliteswithafixedposition overthe
equator.TheinformationiscompatiblewiththebasicGPSsignalstructure,whichmeansanyWAAS‐
enabledGPSreceivercanreadthesignal.

WhobenefitsfromWAAS?
Currently,WAASsatellitecoverageisonlyavailableinNorthAmerica.Therearenogroundreference
stationsinSouthAmerica,soeventhoughGPSuserstherecanreceiveWAAS,thesignalhasnotbeen
correctedandthuswouldnotimprovetheaccuracyoftheirunit.ForsomeusersintheU.S.,the
position
ofthesatellitesovertheequatormakesitdifficulttoreceivethesignalswhentreesormountains
obstructtheviewofthehorizon.WAASsignalreceptionisidealforopenlandandmarineapplications.
WAASprovidesextendedcoveragebothinlandandoffshorecomparedtotheland‐basedDGPS
(differential
GPS)system.AnotherbenefitofWAASisthatitdoesnotrequireadditional receiving
equipment,whileDGPSdoes.


Itjustkeepsgettingbetter
•
100meters:AccuracyoftheoriginalGPSsystem,
whichwassubjecttoaccuracydegradation
underthegovernment‐imposedSelective
Availability(SA)program.
• 15meters:TypicalGPSpositionaccuracy
withoutSA.
• 3‐5meters:TypicaldifferentialGPS(DGPS)
positionaccuracy.
• <3meters:TypicalWAASpositionaccuracy.
http://www.garmin.com/aboutGPS/waas.html