Garmin GPS 60 Owner's Manual - Page 82
Appendix G: WAAS and DGPS, GPS by the U.S. Department of Defense under their Selective Availability
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Appendices Appendix G: 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 spacebased 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 accuracy 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 corrections 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. 72