WAAS - Wide Area Augmentation System

It’s a system of satellites and ground stations that provide GPS signal corrections, giving you up to five times better position accuracy. 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.

WAAS was jointly developed by the United States Department of Transportation (DOT) and the Federal Aviation Administration (FAA), beginning in 1995, to provide precision approach capability for aircraft. Without WAAS, ionospheric disturbances, clock drift (timing), and satellite orbit errors create too much error in the GPS signal for aircraft to perform a precision approach.

The signals from GPS satellites are received across the NAS at many widely-spaced Wide Area Reference Stations (WRS) sites. The WRS locations are precisely surveyed so that any errors in the received GPS signals can be detected.

The GPS information collected by the WRS sites is forwarded to the WAAS Master Station (WMS) via a terrestrial communications network. At the WMS, the WAAS augmentation messages are generated. These messages contain information that allows GPS receivers to remove errors in the GPS signal, allowing for a significant increase in location accuracy and reliability.

The augmentation messages are sent from the WMS to uplink stations to be transmitted to navigation payloads on Geostationary communications satellites.

The navigation payloads broadcast the augmentation messages on a GPS-like signal. The GPS/WAAS receiver processes the WAAS augmentation message as part of estimating position. The GPS-like signal from the navigation transponder can also be used by the receiver as an additional source for calculation of the user’s position.

WAAS also provides indications to GPS/WAAS receivers of where the GPS system is unusable due to system errors or other effects. Further, the WAAS system was designed to the strictest of safety standards – users are notified within six seconds of any issuance of hazardously misleading information that would cause an error in the GPS position estimate.