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GPS Garmin WAAS
You've
heard the term WAAS, seen it on packaging and ads for GARMIN
products, 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.
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![](img/garmin/WASSlogo.gif)
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The
origins of WAAS
The
Federal Aviation Administration (FAA) and the Department of
Transportation 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 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 for 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.
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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.
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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.
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