Garmin GPSMAP 76C User Manual

80
GPSmap 76C
Appendices
WAAS and DGPS
What is WAAS?
The Wide Area Augmentation System (WAAS) is an F.A.A. funded
project to improve the overall integrity of the GPS signal. It is a space-
based system that broadcasts integrity information and correction data as
determined by ground reference stations (see DGPS below). At this time
the system is still in the developmental stage with a goal of providing
reliable signals with an accuracy of 7 meters (21-22 ft.) both horizontally
and vertically 95% of the time. Current tests have shown the actual ac-
curacy to be on the order of 2-3 meters. For more information, go to
http://gps.faa.gov/Programs/WAAS/waas.htm.
What is Differential GPS (DGPS)?
The U.S. and Canadian governments (among others) have set up
Differential GPS (DGPS) stations to transmit correction signals. They are
operational in coastal areas and on many navigable river systems. The
DGPS system is available for use without fee.
In addition to compensating for errors in the position, these correc-
tions signals can also correct for deliberate degradation of the accuracy of
GPS by the U.S. Department of Defense under their Selective Availability
(SA) program.
Refer to the U.S. Coast Guard’s web site: http://www.navcen.uscg.gov/
for locations and the status of the differential sites. Using DGPS requires
additional equipment.
GPSmap 76C Owner's Guide copy.indd 80 3/25/2004, 11:32:20 AM

Garmin GPSMAP 76C Specifications