GPS Technology

The Global Positioning System is a satellite based navigation system made up of a network of 24 satellites placed in orbit by the U.S. Department of Defence.

GPS works in any weather conditions, anywhere in the world, 24 hours a day. There are no subscription fees or setup charges to use GPS.

Each GPS satellite has an on-board atomic clock, and by receiving signals from at least three satellites, the receiver can tell the distance from itself to each one. By triangulation, the position of the receiver is then calculated. The length of time it takes the signal to travel from each satellite to the receiver is slightly affected by the conditions in the outer atmosphere, and this affects the precision which can be achieved without any additional corrections.

	If you try to measure velocity using the change in GPS position over time, then the result is too noisy to be used for any vehicle testing.
	However, when the receiver moves in relation to the satellites, the movement causes a shift in the signals, (the Doppler effect), and these small changes can be measured, and used to calculate Velocity.

	Applying this technology to vehicles can provide useful measurements about the behaviour of a vehicle during testing, and have a number of advantages over existing sensors. They are compact, very quick to fit, accurate, and they work in any weather.