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What
is GPS?
GPS, which stands
for Global Positioning System, is the only system today able to show you your
exact position on the Earth anytime, in any weather, anywhere.
GPS satellites, 24
in all, orbit at 11,000 nautical miles above the Earth. They are continuously
monitored by ground stations located worldwide. The satellites transmit signals
that can be detected by anyone with a GPS receiver. Using the receiver, you can
determine your location with great precision.
GPS is one of
history's most exciting and revolutionary developments, and new uses for it are
constantly being discovered. But before we learn more about GPS, it's important
to understand a bit more about navigation.
The GPS is a
space-based radio-positioning and time transfer system. The GPS has three major
segments: Space Division, Control Segment, and User Equipment Division.
As a universal
positioning system, GPS provides several characteristics not found in other
existing equipment which will enhance the conduct of mission operations:
- Extremely accurate
(3-dimensional) position, velocity and time (PVT) determination
- A worldwide common grid
easily converted to other local datums
- Passive, all weather
operation
- Real-time and continuous
information
- Survivability in a hostile
environment.
How GPS
Works
So you can more
easily understand some of the scientific principles that make GPS work, let's
discuss the basic features of the system.
The principle
behind GPS is the measurement of distance (or "range") between the receiver and
the satellites. The satellites also tell us exactly where they are in their
orbits above the Earth.
It works something
like this: If we know our exact distance from a satellite in space, we know we
are somewhere on the surface of an imaginary sphere with radius equal to the
distance to the satellite radius. If we know our exact distance from two
satellites, we know that we are located somewhere on the line where the two
spheres intersect. And, if we take a third measurement, there are only two
possible points where we could be located. One of these is usually impossible,
and the GPS receivers have mathematical methods of eliminating the impossible
location.
We know that the
GPS system consists of satellites whose paths are monitored by ground stations.
Each satellite generates radio signals that allow a receiver to estimate the
satellite location and distance between the satellite and the receiver. The
receiver uses the measurements to calculate where on or above the Earth the
user is located.
Now that we have
an idea about how the GPS functions, let's see how we can put it to work for
us. As you might imagine, GPS has many uses in both military and civilian life,
such as in the telecomms industry.
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