ST2276
Scientech Technologies Pvt. Ltd.
11
1.
Each satellite emits information relating to its position, relative to the earth and
timing information. This timing information is derived from extremely accurate
atomic clocks (cesium or rubidium) that are synchronized to all other satellite
clocks and to the ground control stations.
2.
GPS Receivers are equipped with quartz clocks that are synchronized to GPS
time via the data transmitted from the constellation.
3.
Timing is the basis of location computation.
4.
The satellite radiates coded signals that are received by the user’s GPS receiver.
5.
The computation in it simplest form is triangulation. Space Based Triangulation
.
Producing Locations :
The determination of position is a simple as the following :
1.
A signal is transmitted from a satellite containing the Time of Departure of the
signal.
2.
The signal is received by the GPS Receiver and the Time of Arrival is
registered.
3.
We know that Radio waves (the signal) travel at the Speed of Light.
4.
We know where the satellite is from the information radiated from the satellite.
Therefore, we can determine the distance from our receiver to a particular satellite.
This allows the construction of a hemisphere, whose centre is the satellite and whose
radius is the calculated distance from a particular satellite to our receiver.
When this process is repeated for another satellite that is in view, then the two
hemispheres with cut through each other. Repeating this process again with a third
satellite and the intersection of the three hemispheres will form a point, which is
where your receiver is located.
This all seems a bit top heavy, but remember that the satellites are constantly
transmitting information and the receiver is usually capable of
producing a location
result up to 10 times every second
.
The accepted rule for most receivers is that the receiver must continuously track a
minimum of four (4) satellites to produce a location that contains a latitude, longitude
and altitude.
Of course most receivers available today will track many more satellites than four (4).
This is important, as mentioned previously, the constellation operates on 12 hour
orbits, therefore the constellation that is visible (being used by the receiver) is always
changing, and hence the receiver needs to be looking for new satellites as the current
in use satellites begin to disappear from view.
Conclusion :
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