Wide Area Augmentation System [WAAS]


Wide Area Augmentation System, or WAAS, is a new satellite-based navigation system built by the U.S. government (FAA) for boating and supplementary navigation for aircraft. It is designed for aircraft landing and has position accuracy as good as 3-7 metres. This will be the best electronic navigation system for recreational users, with GPS a close second.

WAAS-enhanced GPS receivers will be not much more expensive than GPS receivers (contact your manufacturer about upgrading). Canada will need to build their own compatible system - Europe and Japan are already doing this. This should be much more widely used than DGPS, which is only useful around the U.S. and Canadian coastlines.

How does it work

WAAS corrects GPS signals from the 24 orbiting GPS satellites, which can be in error because of satellite orbit and clock drift or signal delays caused by the atmosphere and ionosphere. GPS signsla can also be disrupted by jamming.

WAAS consists of about 25 ground reference stations in the United States that monitor GPS satellite data. Two master stations collect data from these reference stations, assesses signal validity, computes corrections and creates the WAAS correction message. The corrected differential message is then broadcast through two geostationary satellites orbiting over the equator to all WAAS enhanced GPS receivers on the GPS L1 frequency. These satellite each cover a hemisphere, except for polar regions. The receiver (aboard a boat or plane) combines the GPS signals with the WAAS message to arrive at a more accurate position.

Advantages, Disadvantages

Currently, WAAS coverage is only available in North America. Access to the signal is free. You may not be able to receive the signals if trees or mountains obstruct your line of sight to the satellites over the equator. WAAS signal reception is ideal for open land and marine applications. WAAS provides extended coverage both inland and offshore compared to the land-based DGPS (differential GPS) system. Also, WAAS does not require additional receiving equipment; DGPS does.

Other countries are developing compatible systems: the Japanese Multi-Functional Satellite Augmentation System (MSAS), and the Euro Geostationary Navigation Overlay Service (EGNOS). Eventually, GPS users around the world will be able to get accurage position data using similar systems.