GPS Background

GPS Background


Background information on the GPS system and terminology


GPS Background 

GPS Background 



The GPS system that we use each day in our car satnav & handheld GPS units is run by the US Air Force and has been operational since 1995. It uses 24 space satellites each orbiting the Earth every 12 hours, and the system has global coverage. Each point on Earth can generally see four or more satellite.

The satellites orbit at about 24,000 km above the Earth and their ‘messages’ are sent by radio signals sent on the UHF band, and are ‘line of sight’, meaning that the signals will not pass through solid objects such as a tree canopy, cliffs, or buildings, but will travel through clouds.

GPS is the US system. The Russians have GLONASS, Europeans are developing Galileo, and the Chinese and Indians are planning their own systems, although only GPS and GLONASS are operational. The collective name for such navigation systems is GNSS, but for now, any reference to GPS on this site is interchangeable to mean any satellite based location provisioning system.

GPS signals can also be augmented by additional signals, either ground or satellite based. In Europe, the system is called EGNOS, and in the US it’s called WAAS. You don’t really need to know this, but if you see the acronyms in specification sheets for GPS units, you’ll know what they mean.


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Links

  • Lots more background to read on Wikipedia  


Photo courtesy of United States Air Force: photo by Airman 1st Class Mike Meares. Wikimedia Commons