What is DGPS?

By Spirent On May 9, 2012
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DGPS, or differential GPS, is a ground-based enhancement system for the Global Positioning System. The system comprises a network of ground stations, each broadcasting the difference between its known position and its position as indicated by the GPS satellite constellation.

In operation, each DGPS reference station calculates differential corrections for its own location and time. The signals from each station are valid up to 370km from the station. However, because some of the compensated errors vary with space, such as satellite ephemeris errors and the effects of ionospheric and tropospheric distortions, the accuracy of DGPS declines the further the user is from the reference station. Accuracy estimates vary from system to system between 0.22 and 0.67m per 100km from the broadcast site.

The first DGPS system was set up by the US Coast Guard to aid marine navigation. The system grew to cover all maritime routes in and around the USA and Canada, and has subsequently evolved into the US Nationwide DGPS network, covering the entire continental United States. The correction signals are broadcast on long-wave radio at frequencies between 285 and 325kHz. The system is still being expanded, and is planned to eventually comprise 128 ground stations.

Today, 47 other countries operate DGPS networks. These include the European DGPS network, which principally covers the congested waterways between Sweden and Finland. There are also 12 transmitters and three control stations that cover the coastlines of the UK and Ireland.

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