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Wide Area Augmentation System (WAAS)

Contributor(s): Matthew Haughn

Wide Area Augmentation System (WAAS) is a navigation assistance system used to improve the accuracy and precision of global positioning systems (GPS).

WAAS is mainly used in aviation to improve the location-tracking abilities of aircraft. Those abilities are especially important in landing approaches. WAAS helps aircraft land safely, particularly in low-visibility situations.

The signals from GPS are subject to a number of sources of interference that reduce accuracy. Interference from the ionosphere, the atmosphere and satellite orbit errors are common sources of GPS drift. Combining with a ground-level technology to augment GPS satellites’ accuracy can mitigate these factors.

The equipment involved in WAAS is a mixture of satellites and ground stations. A number of stations gather the data across the United States. Two coastal main stations output the corrected signal for relay through satellites. These satellites then provide a corrected GPS signal that makes GPS positioning more accurate. No additional receiving equipment is necessary.

The first GPSs were accurate to 100 meters. GPS without selective availability (SA) restrictions improved accuracy to 15 meters and differential GPS improved accuracy to within 3-5 meters. WAAS is designed to improve accuracy below three meters more than 95 percent of the time. WAAS works best without obstructions and is suited to open areas like plains and the ocean as mountains and other large obstructions can reduce accuracy.

The Federal Aviation Administration (FAA) and the Department of Transportation (DOT) still have WAAS under development. Currently, the system is only available in North America. Other nations’ equivalent technologies include the Japanese Multi-Functional Satellite Augmentation System (MSAS) and European Euro Geostationary Navigation Overlay Service (EGNOS).

This was last updated in November 2017

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