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First time transfer experiment with BeiDou satellites over multiple baselines

In January 2017, two BeiDou time and frequency transfer systems (Fig. 1), which were manufactured by the NIM (China), were installed at BIPM within the framework of the scientific cooperation on time and frequency metrology between the NIM (China) and the BIPM and as part of the long-term activities of Dr LIANG Kun (NIM). The installation of this equipment has allowed the establishment of the first long-distance baseline for clock comparison between the NIM and the BIPM, and evaluation of the performance by comparison with the equivalent GPS observations (Fig. 2). The results of this study have been presented at the European Time and Frequency Forum & International Frequency Control Symposium 2017 (EFTF-IFCS, Besançon, France, July 2017).

The first results over the Europe-Asia link have inspired the initiation of a pilot experiment involving, in addition to the BIPM, other institutes that participate in the key comparison in time CCTF-K001.UTC and which are well distributed throughout the regions: LNE-SYRTE (Paris), PTB (Braunschweig), NIST (Boulder), VNIIFTRI (Moscow), TL (Taipei), NIM (Beijing).

This pilot experiment should pave the way towards the implementation of time transfer with BeiDou in the regular computation of Coordinated Universal Time (UTC). Steps in the roadmap towards this goal are the validation of results obtained over various baselines, the development of the adapted software, and relevant procedures. The calibration of BeiDou systems is an important milestone, and requires cooperation with the French Space Agency (CNES) for realizing the first absolute calibration of a BeiDou receiving system.

This pilot experiment, which resulted from the partnership between the NIM and the BIPM Time Department, will motivate other institutes to incorporate this novel technique.

BDS (BeiDou Navigation Satellite System) is one of four major GNSS systems developed or under development, including GPS, GLONASS and Galileo. Since 27 December 2012, the developing BDS system has provided an official service to part of the Asia-Pacific region and can be used for time and frequency transfer in this area. The BDS system is developing fast; full deployment of satellites, providing global coverage is expected around 2020. For more information on BeiDou, click here.

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