GPSTime Keeping in the Satellite Age

By: Richard N Williams

We are allused to the Sat Nav by now. More and more people are installing those littleblack boxes into their cars and throwing away their old paper road maps. Theadvantages of satellite navigation are many fold – from constant updates keepingthe maps current to being able to pin point your location miles from anylandmarks or road signs.

Currentlythe American Military run the Global Positioning System (GPS) which at presentis the world’s only fully operational Global Navigation Satellite System (GNSS).However, the Europeans have started their own GNSS system called Galileo whichis expected to be fully operational by 2013. Russia and China are also workingon their own systems too.

This will meanmore accurate direction finding for all of us as the differing GNSS areexpected to be interoperable. However, there is more to GNSS than justdirection finding.

GNSSsystems work by using satellites several thousand miles above the Earth’s thatbeam positional information down to a GNSS receiver (like a sat nav).

However toaccurately pinpoint a location, all GNSS systems require an absolute timesource, that is a time source as accurate as humanely possible such as thatfrom an atomic clock. Without knowing exactly what the time is a GNSS satellitewould not be able to accurately pin point a location (as the Earth, satellitesand people are all moving about a location can only be defined by a positionand time). Because of the distance of the satellites away from the Earth, evenan inaccuracy of a second or two could mean a sat nav’s location could be milesout.

As aconsequence of having this accurate time sources, GPS and the new breed of GNSSsystems can all be used to receive an absolute or UTC (Universal CoordinatedTime) time source.

This timesource is currently used by computer networks running a NTP server tosynchronise all machines and devices to the same time.

Having atime signal broadcast all over the world means the entire globe can synchroniseto the exact same timeFind Article, vital in many computer applications.

When thenew GNSS systems are fully functional timing accuracy will also increase alongside accuracy in direction finding.

GPS Vehicle Tracking
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