The international time scales TAI and UTC are computed each month, and the results are published in Circular T, which serves as the monthly update of key comparison CCTF-K001.UTC (new name given for CCTF-K2001.UTC). The stability of TAI, expressed in terms of an Allan deviation, is estimated to be at, or below, 0.4 x 10–15 for averaging times of one month. Twelve primary frequency standards contributed during the period of this report to improving the accuracy of TAI, including eight caesium fountains (IT CSF1, LNE-SYRTE FO1, LNE-SYRTE FO2, LNE-SYRTE FOM, NICT CSF1, NIST-F1, NMIJ F1 and NPL CSF1). A total correction of –3.6 x 10–15 has been applied throughout the year to [ƒ(EAL) – ƒ(TAI)]. Since July 2007, the scale unit of TAI has been estimated to match the SI second to about 1 x 10-15.
Studies on the use of phase measurements along with the code measurements of geodetic-type GPS receivers have concluded, and solutions based on this method (TAI PPP) have been computed in the Section since October 2007 to complete the analysis. In April 2008, a pilot experiment started with the participation of 25 laboratories for studying the introduction of PPP links in TAI. Extensive comparisons of the different techniques and methods for clock comparisons are computed regularly and published on the internet.
Calibration programmes of different types of GPS receivers have been organized and run by the Section. The implementation of a method for the calibration of GLONASS equipment in cooperation with a national laboratory has been concluded, and routine calibrations are under preparation for the second half of 2008.
Support has been provided to the Joint CCL/CCTF Frequency Standards Working Group, in which some members of the staff have responsibilities.
Research work in the Section is dedicated to space-time reference systems. The cooperation with the USNO (United States) for the provision of the Conventions Product Centre of the International Earth Rotation and Reference Systems Service (IERS) is continuing; a workshop on the IERS Conventions took place at the BIPM in September 2007.
Based on the new protocol elaborated by staff of the Section, the key comparison of stabilized lasers renamed CCL-K11 took place in the MIKES (Finland) with the BEV (Austria) acting as pilot laboratory. A member of staff attended the first run of this comparison to provide expertise. The Section has also provided calibration and measurement service of lasers for both internal and external users.
An important number of requests of iodine cells have been satisfied in the year covered by this report. Many of the demands concern specially designed cells with particular geometries.
The work on the gravimeter FG5-108 being made in cooperation with the VNIIM (Russian Fed.) is progressing. In particular, the system for delivering the laser light to the interferometer is under development, and the dropping chamber has been repaired and tested.
Members of the staff participate in activities linked to the special projects at the BIPM. Preliminary studies on the gravimetric equipment and environmental effects on gravity for the watt balance have begun. Work on the construction of the interferometer for the length measurement in the calculable capacitor has progressed during the period of this report.
The Section's staff remained very active in the field of international coordination needed to accomplish the tasks conferred by the Member States. As part of this activity, the physicists of the Section have been widely invited to give lectures at conferences and invited to visit national laboratories. A significant number of articles have been written within the period of this report, and 19 have recently been published with another nine in press at the moment of writing of this report.
Special attention has been provided to training activities for physicists and technicians with the aim of broadening their capacities for the work for which they are responsible.
Summary
