Recommendation 7 of the 20th CCTF (2015)

On the operation and maintenance of Two-Way Satellite Time and Frequency Transfer (TWSTFT) networks for international atomic clock and time scale comparisons

The Consultative Committee for Time and Frequency (CCTF),

considering that

• TWSTFT has been used in the realization of UTC for 16 years,


• about 20 institutes in Asia, Europe, and North America have contributed regularly to UTC with their TWSTFT data, most of them providing their data continuously on a daily basis,


• the Asia-Europe TWSTFT links were interrupted in December 2014,


• regular calibrations offer a time transfer uncertainty at the level of 1 ns, which is the best uncertainty achieved for operational international time transfer,


• having redundant and independent measurement techniques increases the robustness of UTC,


• recent developments in TWSTFT, e.g. employing the carrier phase or software defined receivers (SDR), may dramatically improve satellite based optical clock comparisons over long baselines,


• fibre links are operational only over short distances;

and noting that

• TWSTFT operation relies on satellite services with substantial costs for the participating institutes;

recommends that

• institutes participating in UTC continue to support the TWSTFT activities, including continuous operation of the international TWSTFT network, restoration of the Asia-Europe TWSTFT links and periodic link calibrations,


• new developments in TWSTFT be undertaken to significantly improve remote time and frequency comparisons especially over intercontinental distances and also to reduce costs through the use of new kinds of transmitted signals.

DOI : 10.59161/CCTF2015REC7E