Now
that you have gained some basic knowledge about Trilateration(if not, see
"The math behind the GPS"), you might be wondering and pondering
about how the Radio waves emitted by the Satellites are interpreted by the GPS
receiver to calculate your receiver's distance from these earth-orbiting
Satellites. Just like Trilateration, a simple process is needed in order to
calculate the distance between the GPS receiver and the Satellites. But let’s
first take a look at some basic Scientific concepts:
What are Radio Waves?
Radio waves are low energy electromagnetic waves used for long distance communication. Like all electromagnetic waves, Radio waves travel at the speed of light or at 300 000 km/s.
to understand the following explanations, it is important to know this GOOD, OLD equation!
D = vt
How is the distance calculated?
At a specific time during the day, the Satellite as well as the GPS receiver both emit an identical Pseudo-Random code(a code having a pattern that is sometimes repeated every 7 days!)
When you turn on your GPS receiver, it starts receiving the code emitted by the Satellite. However, the distance the wave has to travel(from Satellite to Earth) creates a slight delay in the reception of the code by the GPS receiver. In other words, the two codes are still identical but the one emitted by the Satellite will lag slightly behind the one emitted by the receiver.
What are Radio Waves?
Radio waves are low energy electromagnetic waves used for long distance communication. Like all electromagnetic waves, Radio waves travel at the speed of light or at 300 000 km/s.
to understand the following explanations, it is important to know this GOOD, OLD equation!
D = vt
How is the distance calculated?
At a specific time during the day, the Satellite as well as the GPS receiver both emit an identical Pseudo-Random code(a code having a pattern that is sometimes repeated every 7 days!)
When you turn on your GPS receiver, it starts receiving the code emitted by the Satellite. However, the distance the wave has to travel(from Satellite to Earth) creates a slight delay in the reception of the code by the GPS receiver. In other words, the two codes are still identical but the one emitted by the Satellite will lag slightly behind the one emitted by the receiver.
This slight incongruity between the two
identical codes is calculated to eventually find the time needed for the code
emitted by the Satellite to reach the receiver.
Once the delay calculated through the use of a highly sophisticated atomic clock, the receiver multiplies the time by the speed of light:
d = Vt
…and subsequently finds its exact distance from the satellite.
An example to clarify things:
What is the distance between Satellite X and receiver Y if the time needed for the radio waves emitted by Satellite X to reach receiver Y is calculated by the GPS receiver to be 0.09 seconds?
-The first step is to identify the variables we know in the equation D = vt
D= ? t= 0.09 s v= speed of light = 300 000 km/s
-The next step consists of solving for D.
D = 300 000 km/s( 0.09 s ) = 27 000 km
The satellite is 27 000 km away from the receiver.
Once the delay calculated through the use of a highly sophisticated atomic clock, the receiver multiplies the time by the speed of light:
d = Vt
…and subsequently finds its exact distance from the satellite.
An example to clarify things:
What is the distance between Satellite X and receiver Y if the time needed for the radio waves emitted by Satellite X to reach receiver Y is calculated by the GPS receiver to be 0.09 seconds?
-The first step is to identify the variables we know in the equation D = vt
D= ? t= 0.09 s v= speed of light = 300 000 km/s
-The next step consists of solving for D.
D = 300 000 km/s( 0.09 s ) = 27 000 km
The satellite is 27 000 km away from the receiver.