NOAA personnel will compile and analyze satellite orbit data from 10 analysis centers worldwide to ensure the accuracy of GPS information. For the next four years NOAA's National Geodetic Survey will serve as the Analysis Center Coordinator for the International Global Navigation Satellite Systems Service, a voluntary federation of more than 200 organizations that provide continuous global satellite-tracking data.

"For GPS receivers to provide accurate information, the precise location of positioning satellites as they orbit the Earth must first be determined," said David Zilkoski, director of NOAA's National Geodetic Survey. "NOAA looks forward to leading this international partnership to produce the highest quality satellite position data possible."

The Global Navigation Satellite Systems, which include the U.S.-based Global Positioning System, the Russian GLONASS system, and the upcoming European Galileo system, are used for accurately determining the geographic position of any point on Earth.

A GPS receiver calculates its position by measuring the time it takes a signal to travel from the satellite to the receiver. Because the signal travels at a known rate and the time is precisely measured using an atomic clock, the receiver can calculate its distance from the satellite. By repeating this process from four or more GPS satellites whose orbits are precisely known, the GPS receiver can determine its position.

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