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Satellite observations

A global navigation satellite system (GNSS) is a system designed for positioning and navigation with the aid of signals received from navigation satellites.

Graphic depiction of satellite orbits
More than 50 satellites are currently orbiting the planet.

The abbreviation GNSS refers to the use of the various existing and future global navigation satellite systems, including:

GPS is a navigation and positioning system of the U.S. Department of Defense (DoD) and is based on a system of 24 satellites which circle the earth twice a day at a height of 20,000 kilometres. During the past 20 years, the USA developed and deployed this system primarily for military purposes.

Equipped with a GPS receiver, this navigation system can be used free of charge.

On 1 May 2000, the USA suspended «selective availability», an artificial distortion of the signals. Users can now determine their position with a degree of accuracy to within a few metres (95% of the observations fall within a circle with a radius of 7 metres). The degree of accuracy largely depends on the satellite configuration and the type of GPS receiver. Higher degrees of accuracy may be attained when using special GPS survey methods.

GLONASS (GLObal NAvigation Satellite System) is the Russian counterpart to GPS. Basically it functions like GPS, but only about half as many satellites are in operation. Further information about GLONASS can be found on the GLONASS homepage.

The planned European satellite navigation system, GALILEO, will include approximately 30 satellites and should be available in 2012. Its function is similar to GPS and GLONASS. However, GALILEO will be operated by civilian authorities and, as opposed to GPS and GLONASS, will also emit integrity signals, which means that it may also be used for applications requiring strict security measures (e.g. in aviation).

BeiDou is the name of the Chinese satellite system, which is primarily used for navigation in Asia. However, it also contains a constellation of around 35 global satellites that can be used for navigation throughout the world.


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Geodesy and Federal Directorate of Cadastral Surveying
E-mail

Federal Office of Topography swisstopo

Seftigenstrasse 264
P.O. Box
3084 Wabern

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