Preliminary views on the future of UTC Chunhao Han Beijing Satellite Navigation Center Information Session, APG4, Thailand, Feb.9-13, 2015

1. Definition and Realization of UTC Definition of UTC UTC was originally approved by the International Radio Consultative Committee (CCIR) in Recommendation 374 of 1963 as the basis for the coordinated broadcast of standard frequency and time signals on allocated frequencies. At that time, frequency offsets and time steps in UTC were announced to be inserted as needed to closely match UTC with the observed rotational speed of the Earth.

1. Definition and Realization of UTC Definition of UTC CCIR Study Group 7 approved in January 1970 a proposal introducing one-second adjustments in UTC, which provides the basis for its current definition. The new system began on 1 January1972. Recommendation ITU-R TF which is incorporated by reference in the Radio Regulations provides the official definition of UTC.

1. Definition and Realization of UTC Realization of UTC UTC is maintained by the International Bureau of Weights and Measures (BIPM) by the contribution from timing laboratories throughout the world and data from the International Earth Rotation and Reference Systems Service (IERS) that determines the rotation angle of the Earth. It is based on the second of the International System of Units (SI). UTC is a critical part of the international infrastructure that requires accurate timing information. As a precise time scale it is essentially an “atomic time” and is also approximately a “mean solar time” in 1 second level.

2. Roles and Functions of UTC UTC is a critical part of the international infrastructure - UTC is the international standard time-scale for all practical timekeeping in the modern world. - UTC provides an approximation value of UT1 for users who need the earth orientation parameters(EOP) UT1-UTC ≤0.9s

The Differences between UTC,UT1 and TAI

3. Deficiencies of UTC The shortcomings or deficiencies of UTC is precisely because it plays two roles. -as the standard time, it is not continuous and uniform; -as the Earth Orientation Parameter UT1, it is not accurate enough. Then it is time to give up that UTC plays two roles!

4. The Impact of Stopping Leap Seconds Used as time in science and technology A continuous standard time scale is very useful and convenient. Stopping the insertion of leap seconds in UTC is the best way to realize a continues time scale. TT=TAI s = UTC+?? TDB=TT+∆T( relativistic period term)

5. The Impact of Stopping Leap Seconds Used as time in civil daily life The civil standard time should has some relations with the mean solar time or the Universal Time (UT1). The impact of time offset between UTC and UT1 is negligible even without leap seconds.  The equation of time is about 16 minutes.  The time difference between the local time and the regional time is much bigger. The offset of the local time to the national standard time is even several hours.

4. The Impact of Stopping Leap Seconds Used as EOP As an approximation of UT1,UTC has wide applications in astronomy,geodesy and space science. Stopping the insertion of leap seconds means that the difference between UTC and UT1 will be no longer a limited value. Then  some hardware and software need some adaptive modifications,  this work will take time and money,  also, there must be EOP services.

5. Preliminary Views A continuous and uniform time scale is the basic goal of the eternal pursuit of science and technology. The irregular insertion of leap seconds in UTC is very inconvenient or troublesome for users that require continuous time scales. The dissemination of two “standard” time-scales might bring significant risks of confusion.

6. Preliminary Views The definition of international standard time must keep some relation with the mean solar time or UT1, the base of civil time is always the sunrise and sunset. A continuous international reference time-scale can be achieved by stopping the insertion of leap seconds in UTC. And as the de facto international standard time, UTC should give up the role of the approximate EOP.

6. Preliminary Views As an approximation of UT1, UTC has wide applications in astronomy, geodesy and space science. If stop the leap seconds, hardware and software in some systems need some adaptive modifications. And this work will take time and money. Taking into account the long history and wide application of UTC, the name and continuity of UTC should keep unchanged. GNSS should provide EOP service.

Thank you for your attention