WAAS - Wide Area Augmentation System

By now, almost everyone is familiar with GPS (Global Positioning System) and if you

own an offshore boat then a GPS receiver is most likely the hub of your navigation equipment. Most offshore mariners have heard the term WAAS used in conjunction with GPS but may not be aware of just what it is.

Wide Area Augmentation System (WAAS) is an enhancement added to the GPS system to increase accuracy. The typical accuracy of 10 to 15 feet is not too shabby considering you're receiving a signal transmitted from satellites over 12,000 miles from Earth that are traveling in excess of 8,000 miles per hour. However, for certain applications such as aircraft precision approaches that just wasn't good enough.

A network of ground-based stations serves as reference points for WAAS. The theory is pretty simple. If you know the exact location of a particular point on Earth then you can take the position from a GPS receiver at that same location and find the "error". From that error factor a correction calculation is derived that can then be used to calibrate the GPS position.

This WAAS correction message is sent to the constellation of GPS satellites approximately 17,280 times every day. WAAS equipped GPS receivers will utilize this information and therefore increase its typical accuracy to about 3 feet or better.

Prior to the introduction of WAAS, the only option for error correction was to incorporate a Differential Receiver into your GPS. Differential is similar to WAAS except that the corrections are send from a series of low frequency land-based transmitters. This required you to have an additional antenna rather than receiving the signal directly from the satellite through your GPS antenna.

Most modern GPS receivers are WAAS enabled and the operator doesn't have to do anything except turn it on and go. WAAS up with that?

WAAS - Wide Area Augmentation System

By: Dave Alston

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