Wide Area Augmentation System
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What is WAAS
Wide Area Augmentation System
WAAS is part of the FAA's plan to retire the existing use of VOR, NDB, ILS, and LOCALIZER aviation navigational systems. WAAS is designed to improve the accuracy and ensure the integrity of information coming from GPS satellites. WAAS will provide accuracy performance of 1 – 2 meters horizontal and 2 –3 meters vertical throughout the majority of the continental U.S. and large parts of Canada and Alaska. One widely anticipated use of this technology will be to provide instrument approaches for aircraft to small airports that don't current offer them. By providing sufficiently accurate location information, a plane would be able to make a precision approach based on an on board database without relying on external glide slope or ILS signals. Combined with TCAS, almost any airport could be usable without relying on expensive on-field equipment.
How it works
WAAS works by providing a series of ground stations that receive GPS signals and transmit corrective information back to another satellite that then provides that information to your GPS receiver. This correction is needed to correct timing errors caused by signal propagation through the atmosphere and other factors that change the timing of the GPS signal.
The information collected by WRS sites is then sent to the WAAS Master Station (WMS) via a terrestrial communications network. The augmentation messages generated at WMSs contain the information that allows GPS receivers to remove the errors in the GPS signal.
The WMSs then send the augmentation messages to uplink stations and finally to Geostationary communications satellites.
Other systems
There is another augmentation system called LAAS. Which like WAAS provides a corrective signal but this is done over a much more local area via a line of sight radio link VHF. This is a short range system just for use around the airport environment.
This system is designed to provide ILS like capabilities to aircraft.
See also
- European Geostationary Navigation Overlay System (EGNOS), the European parallel to WAAS.
External Links
FAA WAAS (http://gps.faa.gov/Programs/WAAS/waas.htm)
FAA LAAS (http://gps.faa.gov/Programs/LAAS/laas.htm)