WAAS stands for Wide Area Augmentation System. It's a system of satellites and ground stations that provide GPS signal corrections, giving position accuracy 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. You don't have to purchase additional receiving equipment or pay service fees to use WAAS.
The Origins Of WAAS:
The Federal Aviation Administration (FAA) and the Department of Transportation are developing the WAAS program for aviation use. WAAS corrects for GPS signal errors and provides integrity information about each satellite, making positioning information more accurate and more reliable. WAAS addresses all of the "navigation problem", providing highly accurate positioning that is extremely easy to use, for the cost of a single receiver installed on the aircraft. Ground- and space-based infrastructure is relatively limited, and no on-airport system is needed. WAAS allows a precision approach to be published for any airport, for the cost of developing the procedures and publishing the new approach plates. This means that almost any airport can have a precision approach, the cost of implementation is dramatically reduced.Additionally WAAS works just as well between airports. This allows the aircraft to fly directly from one airport to another, as opposed to following routes based on ground-based signals. This can cut route distances considerably in some cases, saving both time and fuel. In addition, because of its ability to provide information on the accuracy of each GPS satellite's information, aircraft equipped with WAAS are permitted to fly at lower en-route altitudes than was possible with ground-based systems, which were often blocked by terrain of varying elevation. This enables pilots to safely fly at lower altitudes, not having to rely on ground-based systems. For un-pressurized aircraft, this conserves oxygen and enhances safety.How it Works:Ground reference stations monitor GPS satellite data, and master stations collect data from the reference stations and create a GPS correction message accounting for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere. The corrected differential message is then broadcast through geo-stationary satellites (satellites with a fixed position over the equator). Any WAAS-enabled GPS receiver can read the signal.
WAAS satellite coverage is available only in North America. Other governments are developing similar satellite-based differntial systems - Europe's systemis the Euro Geo-stationary Navigation Overlay System (EGNOS). WAAS receivers are compatible with EGNOS.