WAAS / EGNOS / SBAS
Many people new to GPS are a little daunted by the terms that some GPS users use. One that is frequently mentioned is WAAS, or in Europe - EGNOS or SBAS. This article will explain what WAAS, EGNOS and SBAS is and how it can compliment your position data that your GPS Receiver is receiving from the satellites.

About WAAS
WAAS is something that was originally created for Sh by the American FAA (Federal Aviation Administration), but is now used in consumer grade GPS. WAAS stands for Wide Area Augmentation System. Normally under consumer grade GPS you will be receiving data from up to 12 satellites which will give you a position accurate to 15 meters.

What WAAS does
WAAS basically adds approximately 25 ground stations positioned across the United States of America that monitor GPS data for accuracy. Two master stations are located on the east coast and the west coast collecting data from the reference stations and create a GPS correction message. Sometimes what happens is there are orbit inaccuracies, atomic clock drift and signal delays which can be caused by the earth's atmosphere and ionosphere. The data is then collected and the correctional data is then broadcast through one of two geo stationary satellites orbiting the Earth. Any GPS Receiver that supports WAAS technology will be able to receive this information and can bring the accuracy of GPS down from 15 meters to <3 meters.

Great, you mention WAAS is based in the USA, can I use it outside of the USA ? WAAS really caters for the USA to fine tune the data that's being given, but can be used else where. However there are European systems that augment the current US based Satellites.

  • WAAS Satellites
    • WAAS 1 - PRN 122
    • WAAS 2 - PRN 134

EGNOS - Europe
EGNOS is a system that was designed by the European Union whilst still using the normal US based Department Of Defense GPS satellite constellation, which means you do not have to change your GPS Receiver. Basically if you have a WAAS/EGNOS capable GPS Receiver you will be able to use it in Europe or the US. EGNOS is still currently under test and will be released hopefully to the public by the end of 2004, public trials are currently available and you can pick up signals from the EGNOS satellites, but accuracy cannot be guaranteed until EGNOS goes public.

  • EGNOS Satellites
    • EGNOS 1 - PRN 120
    • EGNOS 2 - PRN 131

About DGPS
DGPS stands for Differential GPS. Accuracy on DGPS isn't as good as WAAS/EGNOS, and will usually give you around 3-5 meters where as WAAS/EGNOS can give you <3 meters accuracy. Most of Garmin GPS Receivers support DGPS apart from the Garmin Geko 101, and all current Magellan GPS Receivers support DGPS except for the Magellan Companion.

SBAS
SBAS is now starting to become the commonly known name for WAAS and EGNOS. SBAS basically stands for Satellite Based Augmentation System

Informational sites on WAAS

Informational sites on EGNOS

Informational sites on DGPS