What is the Garmin WAAS System? — Page 1

What is WAAS?

WAAS stands for Wide Area Augmentation System. You might have heard the term WAAS, or have seen it on packaging and ads for Garmin products. WAAS is a system of satellites and ground stations that provide GPS signal corrections, giving you excellent position accuracy. The WAAS system is an average of up to five times more accurate than the standard GPS. A WAAS-capable receiver can give you a position accuracy of three meters or better 95 percent of the time. And you don't have to purchase additional receiving equipment or pay service fees to utilize WAAS.

Origins of WAAS

The WAAS program was developed by the Federal Aviation Administration (FAA) and the Department of Transportation (DOT) for use in precision flight approaches. Currently, GPS's do not meet the FAA's navigation requirements for accuracy, integrity, and availability. WAAS enabled systems correct for GPS signal errors caused by ionospheric disturbances, timing, and satellite orbit errors, and provides vital integrity information regarding the health of each GPS satellite.

How it Works

WAAS GPS consists of approximately 25 ground reference stations positioned across the United States that monitor GPS satellite data. Two master stations, located on either coast, collect data from the reference stations and create a GPS correction message. The GPS correction accounts for GPS satellite orbit and clock drift plus signal delays caused by the atmosphere and ionosphere. This corrected differential message is then broadcast through one of two geostationary satellites, or satellites with a fixed position over the equator. The information is compatible with the basic GPS signal structure, which means any WAAS-enabled GPS receiver can read the signal.

WAAS vs GPS
100 Meters	Accuracy of the original GPS system, which was subject to accuracy degradation under the government-imposed Selective Availability (SA) program.
15 Meters	Typical GPS position accuracy without SA.
3-5 Meters	Typical DGPS (differential GPS) position accuracy.
< 3 Meters	Typical WAAS position accuracy

Benefitors from WAAS

Currently WAAS satellite coverage is only available in North America. There are no ground reference stations in South America, so even though GPS users there can receive WAAS, the signal has not been corrected and thus would not improve the accuracy of their unit. For some users in the U.S., the position of the satellites over the equator makes it difficult to receive the signals when trees or mountains obstruct the view of the horizon. WAAS enabled GPS signal reception is ideal for open land and marine applications. WAAS Systems provide extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Another benefit of W.A.A.S. is that it does not require additional receiving equipment, while DGPS does.

Other governments are developing similar satellite-based differential systems. In Asia, it's the Japanese Multi-Functional Satellite Augmentation System (MSAS), while Europe has the Euro Geostationary Navigation Overlay Service (EGNOS), also known as WAAS EGNOS. Eventually, GPS users around the world will have access to precise position data using these and other compatible systems.