Gianna Panfilo

Atomic clock prediction based on stochastic differential equations

In this paper we use a mathematical model based on stochastic differential equations to predict the behaviour of atomic clocks. We consider several different cases with deterministic and random signatures and we obtain the best clock prediction together with its uncertainty. The results given by our mathematical model are compared with the results of the traditional method of extrapolating clock behaviour from the past data.Wyye test our methods using experimental data from caesium and hydrogen masers maintained by the Italian time laboratory (INRIM), showing the good performance of our model.

A new prediction algorithm for the generation of International Atomic Time

In this paper we present a new prediction algorithm for the generation of International Atomic Time (TAI). The new prediction algorithm takes into account the frequency drift which affects most of the participating atomic clocks. In particular, we focus on the effect of the application of the new model on the prediction term for the frequency drift affecting the free atomic time scale (EAL). We also present its effect on TAI performance and on atomic clock weights.

The Ornstein?Uhlenbeck process as a model of a low pass filtered white noise

The Ornstein–Uhlenbeck process is presented with its main mathematical properties and with original results on the first crossing times in the case of two threshold barriers. The interpretation of filtered white noise, its stationary spectrum and Allan variance are also presented for ease of use in the time and frequency metrology field. An improved simulation scheme for the evaluation of first passage times between two barriers is also introduced.

Timescales at the BIPM

This paper reviews the present status of the timescales established at the International Bureau of Weights and Measures (BIPM). We focus our attention on the calculation and the characteristics of Coordinated Universal Time (UTC) and present its applications.

Algorithms for International Atomic Time

This article reviews the creation and technical evolution of atomic time scales. In particular, we focus our attention on the method of calculation and the characteristics of International Atomic Time (TAI), and show how it is disseminated at the ultimate level of precision.

UTCr: a rapid realization of UTC

Considering the evolving needs of time metrology and the convenience of allowing the contributing laboratories access to a realization of UTC more frequently than through the monthly Circular T, the BIPM Time Department started in 2012 to implement the computation of UTCr, a rapid realization of UTC published every week and based on daily data. After 18 months of pilot experiment, this new product has been declared operational and is now an official publication of the BIPM. This paper presents the main characteristics and properties of UTCr.

A theoretical and experimental analysis of frequency transfer uncertainty, including frequency transfer into TAI

Results are presented from a theoretical and experimental investigation of the frequency transfer uncertainty (FTU) in long-distance comparisons of frequency standards. The FTU can be an important component of the total uncertainty in such comparisons. The use of the Allan deviation in characterizing the FTU is analysed theoretically and it is shown that for certain noise types the Allan deviation is biased high. A potentially more accurate first difference statistic that can be used in certain situations is also discussed. In addition, an experimental determination of the noise types and levels in common transfer techniques is presented. It is shown that FTUs approaching 1 part in 1016 at 30 days are possible with current transfer methods. Finally, a method is presented for estimating the FTU in calibrating International Atomic Time (TAI) with a primary frequency standard.

Stochastic and reactive methods for the determination of optimal calibration intervals

The length of calibration intervals or measurement instrumentations can be determined by means of several techniques. In this paper, three different methods are compared for the establishment of optimal calibration interval of atomic clocks. The first one is based on a stochastic model and provides the estimation of the calibration interval also in the transient situation, while the others, attain to the class of the so-called reactive methods, which determine the value of the optimal calibration interval on the basis of the last calibration outcomes. Algorithms have been applied to experimental data and obtained results have been compared in order to determine the most effective technique. Since the analyzed reactive methods presents a presents a large transient time, a new algorithm is proposed and applied to the available data.

Algorithms for TAI

The time laboratories realize a stable local time scale using individual atomic clocks or a clock ensemble. Clock readings are then combined at the Bureau International des Poids et Mesures (BIPM) through an algorithm designed to raise the stability, accuracy and reliability of the time scale above the level of performance that can be realized by any individual clock in the ensemble.

Optimal Calibration Interval in Case of Integrated Brownian Behavior: The Example of a Rubidium Frequency Standard

In this paper, two different techniques are considered in order to determine the optimal calibration interval: the intervals that are obtained using a mathematical model and those that are calculated with an iterative technique referred to as a simple response method. It is shown that both techniques provide useful information for an accurate calibration of a rubidium frequency standard. The authors have chosen this example because the degradation of its calibration condition can be modeled by the use of a quite complex stochastic process called the integrated Brownian motion, which is also of interest in other different contexts. The rubidium frequency standard is diffused in industrial calibration laboratories