by Darian Peters

Created on: May 09, 2007   Last Updated: April 11, 2011

A Global Positioning System (GPS, for short) is a technology with multiple uses that allows user with an appropriate receiver to pick up information about his own current position and velocity (speed and direction). This is provided by over two dozen satellites in medium Earth orbit and is accurate up to around 10 metres. The system achieves this using signals of known speed from at least three, but ideally several more, satellites that also carry information about satellite position. This is enough information to work out receiver position using the mathematical method of trilateration.

The GPS system is vital for civilian applications that require any of the three functional aspects of GPS: absolute location, relative movement, and time transfer. Examples of civilian applications utilizing absolute location include navigation and land surveying. This allows accurate maps to be made through its use as a surveying tool. Relative movement can be utilized in vessels at sea, for example, and also for observation of the Earth. Time transfer allows the synchronization of telecommunications networks, in mobile phone base stations, for example. All of the three aspects can be used to study the Earth, such as the atmosphere, earthquakes, and gravity. In the case of earthquakes, for example, GPS has provided much improved measurements of fault motion.

As a dual-use technology, GPS is an important tool not only for civilian applications but also for military applications. Examples of military applications include the precise delivery of weapons including intercontinental ballistic missiles (ICBMs), cruise missiles, and precision-guided munitions, through improved guidance and target tracking. But it can also be used in helping in troop movement, coordination, and logistics, through the use of the Commander's Digital Assistant and the Soldier's Digital Assistant, for Commanders and Soldiers, respectively. GPS can also be used for nuclear detonation detection and also in search and rescue operations.

You would think that, as the name suggests, Global Positioning System is available globally. However, a GPS receiver can be interfered with by electromagnetic radiation overpowering the signal. This interference can occur naturally through solar flares and the geomagnetic storms found at the poles of the Earth's magnetic field. But it also opens up the possibility of someone deliberately jamming the signal. It is believed that GPS-jamming technology was used against American forces in both Afghanistan and Iraq, for example. So reliance on the use of GPS technology alone can be a dangerous strategy.

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