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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.
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
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