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pierredv : metrology   3

Geodesy and metrology with a transportable optical clock | Nature Physics, Feb 2018
Abstract

Optical atomic clocks, due to their unprecedented stability1,2,3 and uncertainty3,4,5,6, are already being used to test physical theories7,8 and herald a revision of the International System of Units9,10. However, to unlock their potential for cross-disciplinary applications such as relativistic geodesy11, a major challenge remains: their transformation from highly specialized instruments restricted to national metrology laboratories into flexible devices deployable in different locations12,13,14. Here, we report the first field measurement campaign with a transportable 87Sr optical lattice clock12. We use it to determine the gravity potential difference between the middle of a mountain and a location 90 km away, exploiting both local and remote clock comparisons to eliminate potential clock errors. A local comparison with a 171Yb lattice clock15 also serves as an important check on the international consistency of independently developed optical clocks. This campaign demonstrates the exciting prospects for transportable optical clocks.
NatureJournal  geodesy  metrology  clocks 
december 2018 by pierredv
IPS - Section Information - About Ionospheric Scintillation - Australian Government, Bureau of Metrology
Contents: About Ionospheric Scintillation What is Ionospheric Scintillation? When and where does Ionospheric Scintillation occur? What is the Impact of Ionospheric Scintillation? Measuring Ionospheric Scintillation Ionospheric Scintillation Monitor (ISM)
satellite  scintillation  australia  metrology  ionosphere 
august 2015 by pierredv
New NIST Time Code to Boost Reception for Radio-Controlled Clocks
"NIST has developed, tested and is now beginning to implement the new phase-modulation WWVB signal. Like a traditional AM radio station, time information is encoded in the WWVB broadcast by changes in the strength or amplitude of the radio signal. Phase modulation adds an additional layer of information encoded by shifting the phase of the carrier wave. (The crests of two waves that are "in phase" pass a point at the same time. If one is phase-shifted, the crest will arrive a little before or after the other.) This change significantly improves signal reception and overall performance of new products that are designed to utilize this new protocol. Legacy clocks and watches will still continue to function as they have because the amplitude modulation remains the same, but they will not benefit from the increased performance of the new phase modulation protocol, Lowe said."
NIST  metrology  time  science  measurement 
march 2013 by pierredv

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