Almost everyone has heard now of the Global Positioning System or GPS. Do you
have an idea how it works? Here is a short and precise GPS review.
The GPS Satellites
There are more than 50 satellites that cover the globe to make it possible for
the GPS to work. At least three satellites need to receive the signal in order
to find the position of a GPS signal. That’s the time the satellites process
information to triangulate the location.
A GPS unit’s function is to acquire the time as accurately as it possibly can.
Here is a basic GPS review: When the satellites receive the signal, they will
compare the time the signal was sent to their own atomic clocks. They will then
figure out how long it took for them to receive the signal, compare the times as
well as their positions with each other, and come up with the location of the
origin of the signal. If three satellites received the signal, they will
transmit the longitude and latitude; if four satellites received the signal,
they will also send the altitude to the GPS unit.
GPS Problems
Based on the basic GPS review outlined above, you can assume that the accuracy
of the time piece in the sending unit can affect the accuracy of the positioning
information. However, errors in clocking are not the main source of error in
GPS. This part of the GPS review explains the other sources of errors.
The atmosphere is the most common source of GPS errors. A signal that passes
through the ionosphere to reach the satellites may get different response.
Depending on the atmospheric conditions, the signal may speed up or slow down,
and this uneven signal speed can affect the time computations. Problems of
inaccuracies increase if the angle that the signal takes increases as it reaches
a satellite. These problems can be corrected, though, especially when the
military, government agencies are surveyors are involved.
If the signal is bounced around by skyscrapers, mountains or other terrain, the
accuracy of GPS is affected. These sources of problems cause signal distortions
that are similar to the atmospheric type. The more sophisticated GPS systems are
able to overcome this problem, though.
Another problem may occur if the satellite updates its location every 12
minutes. Once the signal reaches the satellite near its update time, the
satellite will no longer detect its correct position; the satellite ends up
making an inaccurate calculation. However, this particular problem is almost
negligible for most GPS uses.
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