UTC updates

• Autores: Meynadier, F.; Collini, F.; Harmegnies, A.; Panfilo, G.; Tavella, P.; Tagliaferro, G.; Tisserand, L.
• Año de publicación: 2025
• Idioma: inglés
• Tipo de recurso: documento de conferencia
• Materia: Ciencias Astronómicas; Coordinated Universal Time (UTC); Atomic clocks; Time transfer techniques
• Institución: Universidad Nacional de La Plata

The Bureau International des Poids et Mesures (BIPM) Time department is in charge of the monthly calculation of Coordinated Universal Time (UTC), and its weekly rapid version UTCr. UTC is based on the contribution of about 450 atomic clocks maintained in about 85 time laboratories all over the world compared by means of GNSS, and in some cases by Two-Way Satellite Time and Frequency Transfer. The first step in the computation of UTC is a sort of weighted average of all the clocks to optimize long-term stability. Then the frequency of this average is compared versus the most accurate realization of the second obtained by Primary and Secondary Frequency Standards and a frequency steering is introduced. This process realizes the international atomic time TAI which is a realization of TT as currently defined by IAU in Resolution 4 of its XXIst General Assembly. The last step originated from several discussions taking place in the early ’70s at the IAU (XIVth General Assembly 1970), the Bureau International de l'Heure, the Consultative Committee for the Definition of the Second, and the International Telecommunication Union, which decided to maintain UTC and UT1 in pace within one second with the mechanism of the leap seconds: Since the 1st of January 1972, UTC and TAI differ only by an integer number of seconds, chosen so that it remains within 1 second versus the rotational angle of the Earth UT1. This relies on data communicated by the International Earth Rotation and Reference Systems Service (IERS) through its Bulletin C, and finally enables the publication of UTC. In this presentation, we will summarize the main steps in the computation of UTC, the type of clocks used and the techniques for clock comparisons and the ongoing developments based on the research on new optical frequency standards, as well as new clock comparison techniques. Some recent enhancements on the way UTC is disseminated (i.e. the Circular T, as well as downloadable data available from BIPM’s web server, and the effort towards digitalization) will also be presented.
Facultad de Ciencias Astronómicas y Geofísicas