Time transfer with nanosecond accuracy for the realization of International Atomic Time

Abstract

Two-way satellite time and frequency transfer (TWSTFT) has become an important technical component in the process of the realization of International Atomic Time. To employ the full potential of the technique, especially for true time transfer, a dedicated calibration is necessary. This consists of the calibration either of the operational link at large, including every component involved, or of the involved ground stations' internal delays only. Both modes were successfully employed by circulating and operating a portable reference station between the sites involved. In this paper, we summarize the theoretical background for the different calibration modes applied and report examples of results from the 13 calibration campaigns performed up to now in Europe and between Europe and the United States. In all of these exercises, estimated uncertainties around 1 ns were achieved. Consecutive campaigns showed a very good reproducibility at the nanosecond level. Additionally, we address and briefly discuss sources that possibly limit the uncertainty for true time transfer employing TWSTFT.

Simultaneous remote transfer of accurate timing and optical frequency over a public fiber network

“…Fiber-optical two-way time transfer methods have been demonstrated on dedicated links with an accuracy of the order of 100 ps or better [10,11]. Long-distance accurate time dissemination is usually based on GNSS signals, or geostationary telecommunication satellites, with timing accuracy of the order of 1 ns in the best case [12,13]. In this work, we present a novel method to simultaneously disseminate an ultra-stable optical frequency and accurate timing over a public telecommunication network on a 540-km optical link simultaneously carrying Internet data traffic, using a dedicated ''dark'' channel.…”

International Time Comparison by TWSTFT and GPS at KRISS

“…in the Bureau International des Poids et Mesures (BIPM) and correction campaign was conducted to measure uncertainty as well as adding various contributions (Piester et al 2008). The TWSTFT method for the time comparison has been general in these days so it is utilized to contribute to the time scale by the NMIs or designated laboratories.…”

“…However, the needs of time comparison with such high precision were not required at that time and the TWSTFT was not used actively due to the limitation of satellite utilization and enormous expense such as satellite fee and time comparison devices required to operation the TWSTFT system. However, as precise time measurement and synchronization methods are needed more than ever due to the rapid advancement on frequency standards and communication technology, National Measurement Institutes (NMIs) for time and frequency standardization who construct the TWSTFT time comparison system can be found more and more despite high cost investments and measurement technology has also improved steadily up to 1 ns currently (Kirchner 1991 68 JPNT 5(2), 67-74 (2016) http://dx.doi.org/10.11003/JPNT.2016.5.2.067in the Bureau International des Poids et Mesures (BIPM) and correction campaign was conducted to measure uncertainty as well as adding various contributions (Piester et al 2008). The TWSTFT method for the time comparison has been general in these days so it is utilized to contribute to the time scale by the NMIs or designated laboratories.…”

Study on the Effect of Temperature on the Equipment Delay of Two-way Satellite Time and Frequency Transfer

“…However, the different signal delays were involved in TWSTFT system. So it is necessary to calibrate those delays [2][3][4][5] . In order to calibrate systematic difference any TWSTFT links, we developed two same mobile stations.…”