J. Nawrocki

Comparing a GPS time link calibration with an optical fibre self-calibration with 200 ps accuracy

In Poland, an accurate two-way optical fibre time transfer (TWOTT) baseline of 420 km has been developed with a standard uncertainty of 112 ps. Meanwhile, the BIPM has been engaged in a pilot project to reduce the uncertainty of UTC GNSS time transfer calibrations from 5 ns to approximately 1.5 ns, for which it has developed a standard calibration scheme, named METODE, associated with an integrated portable GNSS calibration station. The TWOTT and the METODE respectively represent the worlds most advanced time transfer method and calibration facility.In July 2013, the BIPM calibrator and the TWOTT self-calibrated optical fibre transceivers were set up side by side to compare their results. This is the first time that an operational TWOTT has been used in accurate time transfer and the first time that a GNSS calibration method has been validated with a technique accurate to 200 ps. As the two systems are completely independent and the latter is one order of magnitude more accurate than the first, this comparison allowed validation of the METODE and its uncertainty. It also confirmed that any bias in the TWOTT is at most 1 ns.

Independent atomic timescale in Poland—organization and results

The Polish independent atomic timescale TA(PL) was officially started on 4 July 2001. It is currently based on the indications of nine clocks from several Polish laboratories and Lithuania. The clocks at the laboratories are compared using TTS-2 multi-channel GPS receivers developed in cooperation with the Bureau International des Poids et Mesures (BIPM). The participating institutions are linked to the Central Office of Measures (GUM) in Warsaw. TA(PL) is computed as a weighted average of the participating clocks. This paper presents the clock ensemble, the data processing outline, and some experimental results.

Recent progress in GLONASS time transfer

Unlike GPS, the GLONASS P-code is broadly accessible. This paper discuss GLONASS capabilities and prospects in terms of precise time transfer. We have tested GLONASS common-view time transfer using the C/A- and P-code, over time links varying in length from about 800 km to 9200 km. The raw GPS and GLONASS data were collected using 3S navigation receivers, and were corrected using IGS precise orbit data and IGS ionosphere maps. It is proposed that GLONASS time links be calculated monthly, initially as backup links for TAI calculation, and later as possible official time links

Multi-channel GPS time transfer and its application to the Polish atomic time scale

Several Polish scientific and commercial institutions are equipped with caesium frequency standards, which can be used for the establishment of a national atomic time scale. The Polish atomic time scale will be computed from a weighted average of the readings of these clocks. All participating laboratories are equipped with a multi-channel GPS C/A code Time-Transfer unit. The structure of this unit is described in brief: the multi-channel method improves the stabilty of the time transfer compared with the single-channel method. The results of such comparisons are presented.

Some tests of GLONASS precise-code time transfer

The current GLONASS constellation presently comprises 15 active satellites which can be used for time transfer. Most characteristics of the GLONASS signal are similar to those of GPS. In addition the GLONASS P-code, unlike the GPS P-code, is available to civil users and it is of great interest to take best advantage of it. GLONASS P-code pseudo-range measurements are considerably more precise than comparable GPS or GLONASS C/A-code measurements. In this paper we describe several tests of the GLONASS P-code for one-site comparison and continental and intercontinental time transfer.

OPTIME - the system grows - a new 330 km line

The OPTIME project creates an ultra-precise time and frequency signals dissemination system based on telecommunication networks. End users obtain access to these signals without incurring huge costs for the purchase of their own atomic clocks, and receive the service related to laboratories generating international atomic time scales, to which any precise time must be referred. OPTIME dissemination system is based on three main elements: reference time and frequency laboratories, local time and frequency repositories and fiber optical network with specialized transmission equipment to transfers signals between laboratories, repositories and end users. This article describes OPTIME system with particular emphasis on a new 330 km long dissemination line between Space Research Centre PAS, Astrogeodynamic Observatory (AOS) at Borowiec and National Laboratory of Atomic, Molecular and Optical Physics (KL FAMO) at Torun.

Towards accurate optical fibre time transfer in UTC

Accurate time transfers are now fully based on space techniques. The recently developed optical fibre technique is expected to be used in the UTC generation in the future. Some UTC labs operate optical fibre links using different approaches. In particular, the here called Two-Way Optical Fibre Time (and Frequency) Transfer (TWOFT/TWOTFT) is of special interest. The symmetry of the propagation conditions in both directions allows to substantially reducing the instability due to fluctuations of the propagation, and its capability of self-calibration. The first operational TWOTT between the UTC laboratories has been established in Poland between AOS and GUM since January 2012. The result has being submitted to the BIPM since March 2013. The BIPM started the monthly data processing and compares to the GNSS links. The TWOTT can reach an accuracy of hundred ps in a few minutes and therefore provide an effective new tool for the assessment of GNSS and TWSTT CP time link calibration and bring substantial improvement to the [UTC-UTC(k)]. However, time transfer by optical fibres today does not match the structure of the UTC time transfer network with a unique pivot. This requires the new network configuration, algorithm and will provoke fundamental changes in the UTC time link computation.

OPTIME — Time and frequency dissemination system based on fiber optical network — PIONIER

The OPTIME project creates a long range dissemination system for transfer ultraprecise time scale and the references frequency signals in telecommunication networks. The highest accuracy signal is available only on fiber optical networks, but other type of networks can be used to transfer of signals with lower accuracy to adapt it to the needs of different user groups. Article also describes experience gained during an over-a-year experiment of connection between Central Office of Measures (GUM) in Warsaw and the Astrogeodynamic Observatory (AOS) in Borowiec.

Preliminary evaluation of the AOS-CsF1 primary frequency standard

We report on operation of a new caesium fountain primary frequency standard at the Astrogeodynamical Observatory of the Polish Space Research Centre. The device was assembled and tested at the National Physical Laboratory in Teddington and subsequently transported to Borowiec where it was fully commissioned in December 2016. We demonstrate its performance in terms of stability in short- and long-term and report preliminary measurements of the systematics effects.

Design and performance of Cs fountain frequency standards constructed for metrology laboratories

Following a refined NPL design, we have constructed several Cs fountain primary frequency standards for use in different metrology laboratories. In this paper we describe the design of these new systems and present measurements of their performance.