LeapSecond.com states: Global Positioning System time is the atomic time scale i

Question

LeapSecond.com states:

Global Positioning System time is the atomic time scale implemented by the atomic clocks in the GPS ground control stations and the GPS satellites themselves.

Does GPS time measure the proper time on the mean sea level (rotating geoid) or the proper time of the GPS station itself?

In other words, is GPS time exactly 19 SI seconds behind TAI time, where an SI second is defined as the proper time on the rotating geoid equal to the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom at rest and at a temperature of 0 K?

Put another way, is GPS time and TAI time simultaneous?

Explanation / Answer

GPS time is locked to TAI time, with a constant difference of 19 seconds as you say. In fact GPS is used as part of the TAI process. See for example tycho.usno.navy.mil/ptti/1993/Vol%2025_13.pdf and

tycho.usno.navy.mil/ptti/ptti2000/paper12.pdf for details.

If you're interested in this area there's a lot of useful stuff on the US Navy web site. Have a Google for something like "gps time site:navy.mil" for lots of useful articles.

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