Recommendation 3 of the 20th CCTF (2015)

On the GNSS time transfer equipment calibration

The Consultative Committee for Time and Frequency (CCTF),

considering that

• the ability to compare the atomic frequency standards for the realization of UTC is dependent on the accuracy and precision of time transfer methods based on Global Navigation Satellite Systems (GNSS) observations,
• the characterization of the delays of GNSS time-transfer equipment is essential to ensure the accuracy of the time links for UTC,
• uncompensated changes of the hardware delays in a time link may cause significant instability in UTC,
• periodic calibration campaigns are necessary to assure an uncertainty at or below 3 ns for the time links included in the computation of UTC,
• the Consultative Committee for the Definition of the Second (CCDS) and subsequently the Consultative Committee for Time and Frequency (CCTF) have stressed in past Recommendations the importance of calibrating the time transfer equipment in laboratories that contribute data for the calculation of UTC at the BIPM,
• the Consultative Committee for Time and Frequency (CCTF), in its Recommendation 2 (2009) and Recommendation 4 (2012), recommended that the Regional Metrology Organizations (RMOs) support the BIPM by organizing campaigns of delay measurements within the framework of regional comparisons to be linked to those conducted by the BIPM;

noting that

• calibration guidelines ve been prepared by the BIPM and the CCTF WG on GNSS time transfer (WGGNSS) and published on the BIPM website,
• among laboratories contributing to UTC, a set of “Group1” laboratories was selected by the RMOs, for which the calibration is organized by the BIPM and from which the calibration of GNSS equipment of the other laboratories should be organized (named “Group 2”),
• significant improvement in time link accuracy is expected from the implementation of this new calibration scheme,
• the BIPM has completed the first calibration of the GPS equipment in Group 1 laboratories and will soon organize the second measurement campaign;

recommends that

• the RMOs or laboratories contributing to RMOs periodically organize calibration trips for Group 2 laboratories,
• the trips be planned in close collaboration with the BIPM, aiming at a complete coverage of Group 2 laboratories,
• these calibrations follow the guidelines published by the BIPM.

DOI : 10.59161/CCTF2015REC3E