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.
Note: This list is not comprehensive.
products ca 2005:
eTrex Legend C
eTrex Vista C
GPS 18 OEM
GPSMAP 76CS GPSMAP 96
GPSMAP 172C GPSMAP 178C
GPSMAP 176C GPSMAP 182
GPSMAP 188 Sounder
GPSMAP 238 Sounder
GPSMAP 60CS GPSMAP 2006
GPSMAP 3006C GPSMAP 3010C
origins of WAAS
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.
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.
benefits from WAAS?
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.
governments are developing similar satellite-based differential systems.
In Asia, it's the Japanese Multi-Functional Satellite Augmentation
System (MSAS), while Europe has the Euro Geostationary Navigation
Overlay Service (EGNOS). Eventually, GPS users around the world will
have access to precise position data using these and other compatible
just keeps getting better