Time and Frequency Metrology

The Time and Frequency Metrology Department carries out research activities in the following fields:

  • Generation of the Italian time scale, time and frequency comparison and dissemination;
  • Atomic frequency standards and frequency synthesis;
  • Algorithm and mathematical methods for metrology and time scales.

Italian time scale UTC(IEN) and synchronisation systems

The generation of the national time scale UTC(IEN) was carried out using five commercial atomic cesium beam clocks and two H masers. During 2005, the mean time offset of the national time scale UTC(IEN) versus UTC computed by BIPM was -32 ns, with a minimum of -118 ns, a maximum of 86 ns and a standard uncertainty of 59 ns. Starting from November 2005, an improved procedure for time scale generation and control is being implemented, allowing a stricter control of the scale behaviour as can be seen in the rightmost part of the graph. The maximum frequency departure of the time scale, in this last period, was 2·10-14.
IEN sent regularly to BIPM the GPS-P3 synchronization data supplied by an Ashtech Z-XII3T geodetic GPS receiver, obtained from the output RINEX files, contributing to a TAI computation performed by BIPM using this kind of data. The RINEX files, supplied by the same receiver, using UTC(IEN) as a reference, have been sent regularly to the GeoDAF data centre of the Italian Space Agency (ASI), to be used by the EUREF Permanent Network, and subsequently by the International GPS Service (IGS).
IEN regularly contributed to the "real-time network prototype" developed and operated by the IGS Real Time Working Group. With this architecture, the real time GPS data provided by the receiver is routed to the Canada Natural Resources archive. Near real-time estimates of the UTC(IEN) time scale are expected as a regular product supplied by the IGS Real Time Project.
In October and November 2005, IEN took part in a calibration campaign to measure the differential delay of the IEN TWSTFT earth station (Two Way Satellite Time and Frequency Transfer) versus other five international laboratories: NPL (UK), OP (F), PTB (D), SP (SE) and VSL (NL). This activity, performed under the responsibility of Joanneum Research (Austria), was carried out by means of a co-location of the transportable reference station TUG01 of TUG (A).
In July 2005, IEN participated in the EUROMET Supplementary Comparison TF.TI-K1 for Time Interval, measuring the delays of some reference cables supplied by BEV (Austria). The calibration involves 27 European metrological laboratories and is still in progress.


UTC(IEN) vs. UTC.


Frequency Standard and Synthesis

During 2005 IEN-CsF1 was operated three times to report TAI calibration data to BIPM (for 25, 40 and 25 days of measurement respectively). The frequency accuracy of IEN-CsF1 was constantly improved, reaching the value of 8·10-16. This improvement was made possible by the reduction of the uncertainties associated with several uncorrected biases like spurious microwave fields and unwanted AC and DC currents.
The work on primary frequency standards also included a new measurement of the DC Stark effect in Cs. Through this measurement it is possible to calibrate the blackbody radiation shift (AC Stark effect); the measurement was done in a buffer gas cell using the dark line technique. This measurement agrees with the result previously obtained with the fountain.
The work on vapor cell frequency standards proceeded with the development of a prototype of Pulsed Optically Pumped Clock, whose short term stability reached 2·10-12, while the long term stability reached the 10-15 range.
During 2005 a new research activity to develop an optical clock based on the highly forbidden optical transition of the Yb atom started. The measurement technique is based on the use of an optical comb generated by a femto-second-width pulsed laser; this comb allows to directly bridge the frequency measurement from microwave to optical frequency. In the figure the frequency spectrum of the ultra-narrow laser pulse is observed after a diffracting prism.


Spectrum of the femto second laser pulse.



Uncertainty budget of IEN-CsF1.


European Satellite Navigation System GALILEO

The Time and Frequency Metrology Department was deeply involved in the development of the Galileo System, for which a Precise Timing Facility is foreseen in order to generate the Galileo System Time. In addition, the support of an external Time Service Provider is expected to maintain Galileo time in agreement with the international standard Universal Coordinated Time (UTC) (see picture).
The main IEN experimental activity was carried out in the framework of the Galileo System Test Bed (GSTB) V1 supported by the European Space Agency (ESA).
In addition, IEN qualified to take part in the subsequent phases of the development started in 2005 and continuing till 2007, namely:

  • Galileo System Test Bed (GSTB) V2, supported by ESA; IEN’s role is the metrological characterization of the on-board clocks;
  • Galileo Phase CDE1, supported by ESA; IEN contributes to the development of the Galileo time laboratory, named Precise Time Facility, by designing the time scale algorithm;
  • Galileo Time Service Provider Prototype, supported by EU; IEN contributes as a UTC(k) laboratory.


    • Galileo timing System.