Estimation of the Scale Unit Duration of Time Scales

Abstract

Primary cesium frequency standards provide physical realizations of the second of the International System of Units, and these are compared with the scale unit of time scales. A method of combining the data from several standards is presented. As an example, this method is applied to the International Atomic Time scale using all the available data from primary standards.

International atomic time: Status and future challenges

“…In step 2, the frequency of EAL is computed by comparison to all available primary and secondary frequency standards using an estimation algorithm [9,10], and a frequency shift (frequency steering correction) is applied to EAL to ensure that the frequency of TAI conforms to its definition. Changes to the steering correction are expected to ensure accuracy without degrading the long-term (several months) stability of TAI, and these changes are announced in advance in the BIPM Circular T. The accuracy of TAI therefore depends on PFS and SFS measurements and on their regular report to the BIPM.…”

“…• the frequency of EAL with respect to the PFS is estimated for each month since 1993 following the algorithm in [9],…”

Studies and possible improvements on the EAL algorithm

“…TT(BIPM) is a time scale optimized for frequency accuracy. It is evaluated annually by making use of all available primary frequency standard data reported to the BIPM by national laboratories[7]-[9].Fig. 3plots the relative frequency of Eal with respect to TT(BIPM08) (black line), and shows that there is a drift of about −1.3 × 10 −17 /day.…”

The Hyperfine Transition for the Definition of the Second

“…The monthly d value and its uncertainty as well as TT(BIPM) and its estimated accuracy are computed with a specific algorithm described in ref. [35] and the computed uncertainties directly depend on the uncertainties reported for the PSFS.…”