Author: Sharmaine
GPS Functionality
We all use the Global Positioning System on almost a daily basis through our GPS devices and applications on our smart phones, but how does the technology actually work?
The Global Positioning System (GPS) is a network of roughly 30 satellites that orbit the earth at a height of around 20,000 meters (dependant on the type). The system was first developed by the United States government for military triangulation and navigation, but now anyone with a Global Positioning System device, whether it is a Sat-Nav, smart phone or handheld Global Positioning System unit, can take delivery of the radio signals that the satellites transmit.
Wherever you might be on the planet, a minimum of four Global Positioning System satellites are ‘visible' at any time. Obviously they are best spotted at night when they reflect the sun's light. Each and every single one transmits data about its position and the present time at systematic intervals.
These signals that travel at the speed of light are intercepted by your Global Positioning System receiver, which works out how far away each satellite is according to how long it took for the messages to be received. Once it has data on how distant at least three satellites are from you, your GPS receiver can pinpoint your location using a procedure called trilateration. The applications for this technology are vast, and many industries such as the aviation industry rely on it.
Try to imagine that you are standing somewhere on earth with three satellites in the atmosphere above you. If you know how far away you are from satellite A, then you know you must be located somewhere on the red circle. If you do the same exercise for satellites B and C, you can work out where you are by seeing where the three circles interconnect. This is exactly what your Global Positioning System receiver does, although it uses overlying spheres instead of than circles. This phenomenon is called trilateration. The more satellites there are above the horizon the more accurately your Global Positioning System unit can determine where you are.
The Global Positioning System is affected by relativity. Global Positioning System satellites have atomic clocks on board in order to keep extremely accurate time. General and Special Relativity, however, predict that variances will be apparent between these clocks and a duplicate clock on earth. General Relativity envisages that time will seem to run at a slower rate under stronger gravitational pull. This means that the clocks on board the satellites will seem to run a bit faster than a clock on earth would. In addition to this, Special Relativity calculates that because the satellites' clocks are moving relative to a clock on the earth, they will seem to run slower.
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