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GPS Technology |
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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.
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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. |
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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.
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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.
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