| WAAS-enabled
products: |
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eTrex® Legend
eTrex Venture®
eTrex Vista®
Geko™ 201
Geko 301
GPS V
GPS 15™H and GPS 15L
GPS 16
GPS 17N
GPS 72
GPS 76
GPS 152
GPSMAP® 76
GPSMAP
76S
GPSMAP 162
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GPSMAP 168 Sounder
GPSMAP 176/176C
GPSMAP 182
GPSMAP 188 Sounder
GPSMAP 196
GPSMAP 232
GPSMAP 238 Sounder
GPSMAP 295
GPSMAP 2006
GPSMAP 2010
iQue 3600
Rino® 110
Rino 120
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You've heard 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.
The origins of WAAS
The Federal 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. Although WAAS has not yet been approved
for aviation, the system is available for civilian use such as
boaters and recreational GPS users.
How it Works
WAAS 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.
Who benefits from WAAS?
Currently, 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.
Other 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 systems.
It just keeps getting better |
