Chuck
11/03/2008
05:10:30 PM
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Re: Measuring distances
Basically, it is multiplying velocity (the speed of a body, e.g. 30 miles per hour) with travel time (for instance 2 hours), and you get the result which is the distance (about 60 miles). But in GPS, we are basically measuring a radio signal, so velocity, which is the speed of light (roughly 186,000 miles per second) is what we multiply against travel time to get the distance of a satellite.
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Cecil
11/03/2008
05:11:30 PM
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Re: Measuring distances
Well that is easy for you to say, but the greatest challenge before we can ascertain the distance from a satellite is to measure travel time. Unfortunately, calculating time is quite tricky; we need to use very accurate clocks to measure travel time.
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Beryl
11/03/2008
05:12:19 PM
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Re: Measuring distances
To determine how long a radio signal takes to reach us from a satellite, a measurement is made on both the satellite and receiver end, using what they call “pseudo-random codes” at exactly the same time. By comparing how late the satellite’s pseudo-random code reaches us compared to the receiver’s code, then we can determine how long the radio signal reaches us.
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Sissy
11/03/2008
05:13:15 PM
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Re: Measuring distances
Finally, if you ascertain the difference in sync of the receiver time minus the satellite time, that will end you up with the travel time. Multiply that travel time by the speed of light and you've got distance.
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