This would seem to lead to a cyclic Self Referencing error so I can only hope that was some how mitigated. It appears TAI currently uses GPS system time to validate the timings between different atomic clocks. I did see one thing in reading that TAI article that I do not have the experience to resolve. UTC itself is derived from TAI (International Atomic Time), which is itself based on a weighted average of 400 atomic clocks spread around the world. It would appear that at least these two GNSS providers reference back to UTC. These two internal times are derived independently of one another but are kept close to the world’s reference time, coordinated universal time or UTC, with the offset between the two being precisely calculated on a continuous basis for the Galileo system by the PTF. Naval Observatory’s Master Clock and steered to Coordinated Universal Time - UTC(USNO), corrected for leap seconds (which GPS time doesn't use). GPS system time, in turn, is referenced to the U.S.
GPS system time is computed by the GPS control segment using an assembly of clocks - the GPS Composite Clock, which consists of all operational monitor station and satellite frequency standards. Galileo runs on Galileo system time (GST), which is generated on the ground at the Galileo Control Center in Fucino, Italy, by the Precise Timing Facility (PTF), based on averages of different atomic clocks. If you want more information you should probably review the article on the main site which may have more up to date information since none of the various systems are completely static. I added emphasis for the specific for this question but included the section for context. When I was doing some Supplemental reading this question prompted I found this archived article from InsideGNSS, which talks about how time is compared between the GPS and Galileo, but also talks about the way the GPS System time is related to UTC. Please look at the respective articles for the direct references to ensure they are the most current, accurate, and provide the proper source references. The clock is ticking.ĭisclaimer: Since I am using Wikipedia references below, this answer itself should not be used as a separate source for a any wiki article. WRC 2023 conference will decide whether leap seconds should continue to be used for another 8 years or die. We use UTC for this purpose $^$: The use of UTC instead of TAI, while usually presented like I did as a need to keep in sync with Sun, is actually based on an imbroglio mixing legal reasons and administration poor understanding of the huge risks and difficulties created by leap seconds for a little practical benefit. So the scale for legal time has to be flexible, unlike TAI. on February 19, to really happen each year at the same legal time. As humans, we expect noon of some day (Sun at its zenith), e.g. While the TAI scale is invariant, the year duration varies, mostly due to Earth decreasing rotation rate under the braking effect of tides.
End of 2021 the relationship is this one: In addition GPS time and UTC were equal on January 6 1980. GPS time unit and UTC time unit are the TAI second. Both GPS time and UTC are derived from the atomic time TAI, a reference used to define the time unit in SI, kept by 400 atomic clocks in the world.
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