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ITU continues debate on future of “leap second”

ITU continues debate on future of “leap second”

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By eeNews Europe



Although apparently an arcane subject, this debate has implications for many electronic systems that use a variety of broadcast standards to maintain their timebases – not least, worldwide communications systems, and the operating systems in connected portable devices. And, familiar names in the test & measurement industry supply many of the clocks that act as references for those standards.

At issue is the future of UTC. To date, UTC has been periodically re-sychronised to the rotation of the Earth by adding “leap seconds”. This is essentially a random process as the Earth’s rotation is unpredictably slowed by weather systems, tidal and geological forces. GPS time (to cite one contrasting standard) has counted continuously from a baseline and is not so corrected, and is therefore “out of step” with UTC. A proposal has been extensively debated that UTC should no longer be corrected; this would make it a continuous time standard but at the cost of having it slowly drift out of synchronisation with astronomical time. In 2012 the ITU decided, in effect, not to decide, and deferred making any changes; this past week has seen the latest step in the process, and the ITU’s statement on the subject says;

“The future of the International Time Scale has been the subject of intense discussion this week at a workshop held jointly by ITU and the International Bureau of Weights and Measures (Bureau International des Poids et Mesures – BIPM). At the heart of the matter is the proposal to abolish the so-called ‘leap second’ to adjust to the earth’s rotation in relation to Coordinated Universal Time (UTC), the current standard for measuring time. The suppression of the leap second would make continuous time scale available for all the modern electronic navigation and computerised systems to operate with and eliminate the need for specialised ad hoc time systems.

“ITU membership along with other organizations has been studying the consequences of eliminating the leap second for several years.

“In January 2012, the ITU Radiocommunication Assembly deferred the decision to develop a continuous time standard that would entail the elimination of the ‘leap second’ in order to ensure that all technical options have been fully addressed before the matter is referred to the next World Radiocommunication Conference in 2015.

“During the workshop held this week in Geneva, information sessions on the definition of the time scale along with the maintenance of UTC (or ‘clock time’) in relation to the Earth Rotation Angle (UT1) were followed by discussions on the elimination of the leap second and opting for a continuous time scale. Representatives of the world’s major global navigations satellite systems (GNSS), such as the U.S. GPS, the Russian GLONASS, the European Galileo and the Chinese Beidou, participated in the discussions.”

“Timekeeping is critical to the functioning of modern society,” said ITU Secretary-General Hamadoun I. Touré. “International coordination is crucial and we need to address all options and opinions ahead of the World Radiocommunication Conference in 2015 when Member States will consider the feasibility of achieving a continuous reference time scale.”

“Defining, maintaining and realizing the reference time scale is the result of continuous coordination between groups of international organizations,” said Elisa Felicitas Arias, Director of Time Department, BIPM. “In the event that ITU Member States approve a continuous reference time scale, IERS will continue to guarantee the predicted values of UT1-UTC, ITU would make specific recommendations for the dissemination of those values, and BIPM would remain responsible for the maintenance of the reference time scale as part of coordinated international efforts.”

The International Bureau of Weights and Measures (BIPM) maintains UTC in cooperation with the International Earth Rotation and Reference Systems Service (IERS) along with some 70 national institutes worldwide.

The Director of ITU’s Radiocommunication Bureau François Rancy said, “A variety of systems using UTC have been developed over the past 40 years since the introduction of the leap second and proponents argue that UTC should be maintained. Strong arguments are also made to abolish the leap second in favour of a continuous reference time scale as a measure to increase the reliability of systems that depend on time to reduce costs and avoid unnecessary disruptions. This workshop, organized by ITU and BIPM, provides a very important platform for exchanging information and views on the different perspectives in an effort to prepare for the World Radiocommunication Conference in 2015 which will consider the possible suppression of the leap second.”

ITU; www.itu.int

[Salvador Dali’s The persistence of memory is in the collection of the Museum of Modern Art, New York]

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