Here are some details on the gravity measurements: http://projects.npl.co.uk/itoc/project-structure/reg/gravity-observations/
AFAIK this campaign is done with GPS-PPP and TWSTFT for frequency comparison. The troposphere makes it hard to reach 1e-17 level for the satellite links - even with a week of averaging time. The next step is coherent frequency transfer over optical fibers, where they claim down to maybe 1e-18 or 1e-19 ADEVs for the link itself for a day of averaging. Anders On Sat, Jun 6, 2015 at 3:19 AM, Richard (Rick) Karlquist < [email protected]> wrote: > Can someone explain to me how this is going to work in > light of the fact that each clock is in a different > gravitational field? Or is accuracy not the measurement, > but rather stability? No, that can't be because any > lab that wants to measure stability merely needs to build > two or three copies of their favorite clock and insure > against synchronization. They in principle shouldn't > need to compare against a dissimilar type of clock. > Therefore, we are back to the gravity issue. > > When we worked on the 5071A, we barely had enough sensitivity > to notice a few parts in 10^13 between Santa Clara and > Boulder (~5000 feet). > > Rick Karlquist N6RK > > On 6/3/2015 12:18 AM, Hal Murray wrote: > >> Nice picture: A strontium-ion optical clock housed at the National >> Physical >> Laboratory in Teddington, UK. >> >> Over the past decade, various laboratories have created prototype optical >> atomic clocks, which use different elements such as strontium and >> ytterbium >> that emit and absorb higher-frequency photons in the visible spectrum. >> This >> finer slicing of time should, in principle, make them more accurate: it is >> claimed that the best of these clocks gain or lose no more than one second >> every 15 billion years (1E18 seconds) -- longer than the current age of >> the >> Universe -- making them 100 times more precise than their caesium >> counterparts. Optical clocks are claimed to be the best timekeepers in >> existence, but the only way to verify this in practice is to compare >> different models against each other and see whether they agree. >> >> Starting on 4 June, four European laboratories will kick off this testing >> process -- the National Physical Laboratory (NPL) in Teddington, UK; the >> department of Time-Space Reference Systems at the Paris Observatory; the >> German National Metrology Institute (PTB) in Braunschweig, Germany; and >> Italy's National Institute of Metrology Research in Turin. Between them, >> the >> labs host a variety of optical clocks that harness different elements in >> different experimental set-ups. >> >> >> _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
