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Navigation


Navigation

    • Precise time is essential for precise navigation.
    • In the past, navigation has been a principal motivator in man's search for better clocks
    • Even in ancient times, one could measure latitude by observing the stars' positions. However, to determine longitude, the problem became one of timing
    • Since the earth makes one revolution in 24 hours, one can determine longitude from the time difference between local time (which was determined from the sun's position) and the time at the Greenwich meridian (which was determined by a clock): Longitude in degrees = (360 degrees/24 hours) x t in hours.
    • Today's electronic navigation systems still require ever greater accuracy. As electromagnetic waves travel 300 meters per microsecond, e.g., if a vessel's timing was in error by one millisecond, a navigational error of 300 kilometers would result.
    • In the Global Positioning System (GPS), atomic clocks in the satellites and quartz oscillators in the receivers provide nanosecond-level accuracies. The resulting (worldwide) navigational accuracies are about ten meters
    • Global positing systems are composed from two main systems: the satellite and the satellite base stations. These include atomic clocks on board as THE key element. Stable and accurate frequency is also required in the satellite's base stations.

     

     

 

 

 

 



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