The cooperation with the INRIM and the USNO for the calculation of uncertainties of [UTC – UTC(k)] continues; the method was refined and the uncertainties have been published in the Circular T and in the monthly updates of key comparison CCTF-K2001.UTC. The stability of TAI, expressed in terms of an Allan deviation, is estimated to be about 0.4 x 10–15 for averaging times of one month. Eight primary frequency standards contributed during the period to improve the accuracy of TAI, including four caesium fountains (IT CSF1, LNE-SYRTE FO2, NIST-F1, and NMIJ F1). A total correction of –6 x 10–15 has been applied throughout the year to [f(EAL) – f(TAI)]. Since July 2005, the scale unit of TAI has been estimated to match the SI second to within (1 to 2) x 10–15. To improve the accuracy of TAI arising from the contributions of primary frequency standards, the Time Section is working closely with the new CCTF Working Group on Primary Frequency Standards.
New methods of clock comparison based on GPS observations have been studied for a future application in the calculation of TAI. Extensive comparisons of the different techniques and methods for clock comparison are computed regularly and published on the internet. Two ad hoc study groups have been established by the CCTF Working Group on TAI to investigate the optimization of time links for TAI. Calibration programmes of existing GPS receivers have been organized and run by the Time Section, and calibration of new types of GPS receivers and of GLONASS receivers have been investigated.
Support was provided to the Joint CCL/CCTF Working Group on Secondary Representations of the Second, in which some members of the staff have responsibilities. The section has been involved in discussions with experts from NMIs concerning the need for improvement in the performance of remote comparison techniques in order to take advantage of the performance of optical clocks for the international time scale.
Research work is also dedicated to space-time reference systems, particularly to the relativistic framework for defining and realizing coordinate times. Within 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), a user discussion forum has been set up. Updates of the IERS Conventions (2003) have been published on the Conventions website, which is maintained at the BIPM.
An external audit of the quality procedures of the Time Section took place in April 2006. As a result, the auditor qualified the work as well organized, and suggested only some minor changes in procedures and technical instructions.
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