Pierre Uhrich

Performance assessment of the time difference between EGNOS-network-time and UTC

The European SBAS (Satellite Based Augmentation System) EGNOS (European Geostationary Navigation Overlay Service) provides in its navigation message the time difference between EGNOS Network Time (ENT) and UTC. For that purpose, an EGNOS ground station was installed in the Observatoire de Paris (OP) and is connected to UTC(OP). Applying EGNOS corrections on GPS measurements provides a precise time and navigation solution referenced to ENT. Therefore the assessment of the time difference between ENT and UTC is a key issue for time users. A new EGNOS system release has been tested since the beginning of 2008, it includes some improvements in the timing functions. This paper deals with the evaluation of the performances obtained by these functions.

Use of two traveling GPS receivers for a relative calibration campaign among European laboratories

We report about a GPS receiver relative calibration campaign, which took place between five European National Metrology Institutes or Designated Institutes: LNE-SYRTE in Observatoire de Paris (Paris, France), where the reference receiver of the campaign was located, ROA (San Fernando, Spain), SP (Borås, Sweden), PTB (Braunschweig, Germany) and INRIM (Torino, Italy). We used as traveling equipment two main units, both connected to a single antenna, and we kept track of the offset between both traveling units in all the visited sites. An external validation of the resulting hardware delays is provided against the time scale differences derived from the UTC - UTC(k) data published by BIPM in its monthly Circular T. Thanks to a very good stability of the traveling equipment, we obtained expanded uncertainty estimates within 2.0 ns (k = 2) for the hardware delays.

Steering of the French time scale TA(F) towards the LNE-SYRTE primary frequency standards

The French atomic time scale TA(F), which is computed with data from about 20 industrial caesium standards located in nine French institutions, aims to provide a stable national frequency reference to the contributing institutions. To improve its stability, it was decided a few years ago to steer the time scale, which up to that date was free running, on the LNE-SYRTE primary frequency standards (PFS). The frequency of TA(F) was first slowly corrected monthly by an arbitrary given frequency offset with respect to TAI, to compensate the drift without disturbing the 30 d relative frequency stability of the time scale. Once close enough to the SI second, the time scale was steered monthly to the frequency data issued from the LNE-SYRTE PFS, in that way providing a more stable reference. We describe the steering applied to TA(F) and show the results in terms of relative stability with respect to TAI, or by comparing TA(F) with the SI second on the geoid as published monthly by the BIPM in its Circular T. When applying this steering during recent years, the departure over 30 d intervals of TA(F) from the SI second on the geoid was maintained inside the limits ±3 × 10−15. Within these limits, the TA(F) scale unit interval is in agreement with the SI second, a result which was made possible thanks to the four PFS currently in operation in the LNE-SYRTE.

The Time Validation Facility (TVF): An all-new key element of the Galileo operational phase

In the Galileo FOC phase (Full Operational Capability), GMV is the prime contractor for the Time and Geodetic Validation Facility (TGVF), a contract of the European Space Agency (ESA). Within the TGVF, the Time Validation Facility (TVF) is the subsystem in charge of steering Galileo System Time (GST) to UTC, among other duties. The new TVF is operated at GMV headquarters near Madrid, Spain. TVF operations rely on the contribution of five European timing laboratories, located at INRiM, OP, PTB, ROA, and SP. This paper provides a general description of the TVF element and its related activities for the FOC phase, and presents the main results and findings of the TVF operation until now.

GPS time link calibrations in the frame of EURAMET Project 1156

Since 2010 ROA has supported the coordination of the EURAMET Technical Committee for Time and Frequency (TC-TF) Project 1156, a response from EURAMET TC-TF to Recommendation 2 of CCTF 2009: to study the characterization of GNSS equipment in use for establishing the time links between institutes contributing with their clocks to TAI. Starting that year, a GPS calibration campaign was organized between three contributing laboratories: ROA (Spain), PTB (Germany) and INRIM (Italy). The time transfer results were achieved by using the P3 method, and also carrier phase PPP comparison techniques. These results were also used to re-calibrate the TWSTFT (Two-Way Satellite Time and Frequency Transfer, TW for short) links between labs, with an uncertainty slightly higher than that of the GPS links. During 2011 and 2012, the campaign was repeated, and in 2012 two other laboratories were included in the calibration trip: NPL (United Kingdom) and OP (France). In this paper we report the calibration results, with a focus on the long term stabilities of the GPS and TW links between the visited labs.

Performances of UTC(OP) based on LNE-SYRTE atomic fountains

We present the current realization of UTC(OP) generated at LNE-SYRTE, Observatoire de Paris (OP), Paris, France, which is also the source of French legal time. UTC(OP) is based on a H-Maser standard steered on the atomic fountains developed by LNE-SYRTE. The steering algorithm and the prediction of UTC(OP) departure from UTC are described, together with the results of the first year of operation. Since October 2012, the departure of UTC(OP) from UTC stayed well below 10 ns.

Techniques of antenna cable delay measurement for GPS time transfer

We compare the measurement results of antenna cable delay obtained from six different techniques, including some that allow the measurement of the cable installed in-situ. Among these techniques, the reflection of a pulse from the open end of the cable is described and compared with the results obtained with all the other techniques. We obtain a sub-ns consistency between all techniques for three cables of different types, the best technique, based on a Vector Network Analyzer, providing an uncertainty we estimate within 100 ps.

Current status of the French Atomic Time scales TA(F) and UTC(OP)

The LNE-SYRTE in Observatoire de Paris (OP), Paris, France, is the National Metrology Laboratory in charge of the French Time and Frequency References. In that frame, two atomic time scales are currently generated: the French Atomic Time TA(F) and the real time prediction UTC(OP) of the future UTC. TA(F) is a common frequency reference based on commercial clocks disseminated in nine French institutions or companies. It has been recently improved both in terms of accuracy and long term stability thanks to the steering on the LNE-SYRTE Primary Frequency Standards (PFS) which realize the definition of the SI second. During the last three years, the TA(F) scale unit interval stayed globally close to the SI second on the Geoid, as published monthly by the Bureau International des Poids et Mesures, within a 1.8 × 10−15 limit, exhibiting virtually no drift. This result was made possible thanks to the four LNE-SYRTE PFS, which include three fountains currently in operation. On the other hand, a new UTC(OP) is under development. The signal from one Hydrogen Maser is steered in frequency on an ensemble clock based on OP industrial Cesium standards. In addition, to steer the timescale towards UTC, we apply to the ensemble clock a frequency correction derived from a comparison to the laboratory PFS and from the departure of TAI from the SI second: the goal here is not to be aligned with the SI second, but to stay as close to UTC as possible. This new UTC(OP)_Maser is aiming at staying within a 30 ns departure from UTC. First results obtained from the current operational system are showing that this should be feasible. Current tests are mostly about reliability issues, an essential step before this new time scale will replace the former system.

Time and frequency transfer by geodetic GPS: Comparison of receivers and computation techniques

Geodetic GPS techniques based on dual-frequency phase and code measurements are now commonly used to perform time and frequency transfer. We present results from a dedicated experiment carried out to compare different types of geodetic GPS receivers and different processing techniques. Two time laboratories provide data from three different types of receivers as well as from Two-way time transfer and this dedicated data set is completed by data obtained from other laboratories participating to TAI. Comparisons of results between GPS analyses with two software packages and two processing techniques, and between GPS and TW are presented and discussed.

Stability analysis of the French timescale UTC(OP)

This paper presents the current results obtained with the new version of the French timescale UTC(OP) in operation since more than two years now. The time scale is based on an hydrogen maser steered by one of the SYRTE atomic fountains. Thanks to this technique, UTC(OP) is one of the best real time realization of UTC. A statistical analysis of different UTC - UTC(k) comparisons is presented.