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 |
