|
What is 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.
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.
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 |
