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WAAS Enabled
What is WAAS?
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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