G01 Reference Frames

IAG (Geodesy)

28-Jun-2015, 15:00 - 16:30

Abstract content:

International timescales with optical clocks

A prerequisite for a redefinition of the SI second based on optical atomic clocks is their integration into the international timescales TAI and UTC. This requires a coordinated programme of clock comparisons to be performed, to validate the uncertainty budgets of the optical clocks, to anchor their frequencies to the present definition of the second, and to establish the leading contenders for a new definition. Such a programme is underway within the EMRP-funded project “International Timescales with Optical Clocks” (ITOC), involving optical clocks in five different laboratories. Several new measurements have already been completed and the current status will be reported at the conference. New methods developed to analyze the self-consistency of the clock comparison data and to derive optimized values for the frequency of each optical clock transition will also be described.

To support this programme, an evaluation is being made of all relativistic effects influencing time and frequency comparisons at the 10-18 level of accuracy, including the gravitational redshifts of the clock transition frequencies. Significant progress has been made towards improved determination of the gravity potential at the sites participating in the clock comparisons; gravity surveys have been carried out at all locations and will feed into the computation of a revised European geoid model.

An experiment is also being prepared to demonstrate the impact that optical clocks could have on the field of geodesy. This aims to measure with high temporal resolution the gravity potential difference between two well-defined locations separated by a 90 km baseline and a height difference of 1000 m.

H. Margolis1, E. Benkler2, D. Calonico3, H. Denker4, P. Delva5, R. Godun1, C. Lisdat2, J. Gersl6, M. Merimaa7.
1National Physical Laboratory, NPL, Teddington, United Kingdom.
2Physikalisch-Technische Bundesanstalt, PTB, Braunschweig, Germany.
3Istituto Nazionale di Ricerca Metrologica, INRIM, Torino, Italy.
4Leibniz Universität Hannover, Institut für Erdmessung, Hannover, Germany.
5LNE-SYRTE / Observatoire de Paris, LNE- CNRS- UPMC, Paris, France.
6Cesky Metrologicky Institut, CMI, Brno, Czech Republic.
7MIKES Metrology, VTT Technical Research Centre of Finland Ltd, Espoo, Finland.


Optical clocks     International timescales