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GPSMAP 76CSx Owner’s Manual 97
APPENDIX > WHAT IS WAAS/EGNOS?
What is WAAS/EGNOS?
The Wide Area Augmentation System (WAAS) is an
FAA funded service to improve the overall integrity of
the GPS signal for users in North America. In Europe,
WAAS is referred to as EGNOS.
The system is made up of satellites and 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 data
correction message.
According to the FAA’s Web site, testing of WAAS in
September 2002 confirmed an accuracy performance
of 1-2 meters horizontal and 2-3 meters vertical
throughout the majority of the continental United
States and portions of Alaska.
WAAS is just one service provider that adheres to the
MOPS (Minimum Operational Performance Standard)
for global Satellite Based Augmentation Systems
(SBAS). Eventually there will be several services of
worldwide geostationary communication satellites
that broadcast integrity information and differential
correction data as transmitted by ground reference
stations.
All SBAS systems use the same receiver frequency;
therefore any operational SBAS system should be
capable of providing your GPS unit with increased
accuracy at any location in the world.
Currently, enabling WAAS on your GPSMAP 76CSx
in regions that are not supported by ground stations,
may not improve accuracy, even when receiving
signals from an SBAS satellite. In fact it can degrade
the accuracy to less than that provided by GPS
satellites alone. For this reason, when you enable
WAAS on your Garmin GPS receiver, the receiver
automatically uses the method that achieves the best
accuracy. To enable or disable WAAS, see page 66.
For more information, go to http://gps.faa.gov/
Programs/WAAS/waas.htm.