GPS Handout - UMaine ECE Department

What we'll cover:
A. What is it?
B. History of development
C. How does it work?
D. What are the environmental applications of GPS?
A. What is it?
GPS stands for _________________________.There are _____
satellites circling the earth, owned by the US Department of
Defense. These satellites emit a signal in the form of a radio
wave and the GPS receiver receives the signal, and its computer
calculates its position. When signals for at least ______ satellites
are received at once, your position can be calculated in three
dimensions: latitude, longitude, and elevation.
B. History of development
The system was developed by the United States Department of Defense to
simplify accurate navigation. From 1978-1994 the NAVSTAR satellites
were built and launched _________________into space. The NAVSTAR
satellites are on call anywhere in the world __________a day ___________
a week.
C. How does it work?
The GPS receiver calculates your position using a process called triangulation. In order
for the GPS receive to triangulate your position two pieces of information are needed:
1) __________________________________?
2) _____________________________________________?
So how can the distance from you to the NAVSTAR satellites be measured?
The formula for distance is:
The velocity of the waves that the satellites emit is _____________________________.
This also known as the __________________________!!!! Precise clocks are used in the
receivers and the satellites and they both generate the same code at the same time.
Now, because it takes awhile for the signal to travel through space from the satellite to you,
when you compare the code being received from the satellite with the same code being
generated by the receiver, at the same time, they do not match. The differences in these
codes tell us the travel time. Since we already know the velocity, the distance can be
Lets see how long it might take for a signal to reach earth.
D. Accuracy of GPS
There are a number of reasons why GPS isn't more accurate. For instance, the radio signal sent
from the satellite can bounce off other objects on its way to you, and therefore the timing is thrown
off. But the biggest reason is something called ____________________________.
Selective availability: In the past the US Department of Defense created clock errors in the satellite
clocks in order to reduce the user’s ability to collect accurate position data. This reduced the
accuracy of the GPS to 100 meters. Now however the government has allowed accuracy to reach
E. What are the environmental applications of GPS?
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