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102 GPSMAP 188/188C Sounder Owner’s Manual
APPENDIX > WHAT IS A 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. WAAS
testing completed in September of 2003 confirmed an accuracy of 2
to 3 vertical meters throughout the majority of the continental U.S.
and portions of Alaska. For more information, go to
http://gps.faa.gov/Programs/WAAS/waas.htm.
NOTE: If you are using the GPSMAP 188/188C Sounder
outside of the U.S.A, we recommend you turn off WAAS for the
most accurate location fix.
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 a fee.
Refer to the U.S. Coast Guard’s Web site, http://www.uscg.gov/
for locations and the status of the differential sites. Using DGPS
requires additional equipment.