Wide Area Augmentation System (WAAS): More Accurate GPS

(GPS needed more accuracy; so, now we have WAAS)

An Extension of GPS

The basic GPS service fails to meet the accuracy, availability and integrity that are needed by many people using the GPS system; therefore, some type of differential correction is needed to improve the accuracy of the GPS signal. A system being developed in the U.S. to provide differential correction is the WAAS system.

In order to meet the requirements for accuracy and integrity the U.S. Federal Aviation Administration (FAA) is developing the Wide Area Augmentation System or WAAS. It is what the name implies, a geographically expansive augmentation to the basic GPS service. WAAS improves the accuracy, integrity, and availability of the basic GPS signals. This system will allow GPS to be used as a primary means of navigation for enroute travel and non-precision approaches in the U.S. The wide area of coverage for this system includes the entire United States and some outlying areas such as Canada and Mexico.

WAAS is based on a network of approximately 25 ground reference stations that covers a very large service area. Signals from GPS satellites are received by wide area ground reference stations (WRSs). Each of these precisely surveyed reference stations receive GPS signals and determine if any errors exist. These WRSs are linked to form the U.S. WAAS network. A correction message is prepared and uplinked to a GEO via a ground uplink system (GUS). The message is then broadcast on the same frequency as GPS) to receivers which are within the broadcast coverage area of the WAAS. The communications satellites also act as additional navigation satellites for the aircraft, thus, providing additional navigation signals for position determination.

Signal Available as of August 26, 2000

After a successful 21-day stability test of the Wide Area Augmentation System (WAAS) signal in space, the U.S. Department of Transportation's Federal Aviation Administration (FAA) declared that it is available for some aviation and all non-aviation uses. The test demonstrated that the system can operate without interruption, providing a stable and reliable signal to augment GPS.

For non-aviation users, the signal supports a variety of applications in recreation, boating, agriculture and surveying. The system provided one to two meters horizontal accuracy and two to three meters vertical accuracy throughout the contiguous United States. Raytheon will operate the system for the FAA on a continuous basis, interrupting it only as necessary to upgrade or test the system.

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