Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/iau-comm31/pdf/Leap_sec_RS_Discn_Meeting.pdf Дата изменения: Wed Dec 21 02:58:44 2011 Дата индексирования: Tue Oct 2 06:58:56 2012 Кодировка: Поисковые слова: m 81

UTC for the 21st Century
Discussion meeting held at the Royal Society Kavli International Centre on 3rd and 4th of November 2011 Organizers, Dr Terry Quinn CBE FRS, Emeritus Director of BIPM Among the points discussed1 were the following:
1. Needs for precise timing There exists a broad spectrum of needs for precise timing, extending from the most demanding requirements of satellite navigation systems for a continuous atomic time scale accurate at the level of nanoseconds, through the increasing number of precise time-
stamping or dating systems working at the level of milliseconds, to the far end of this spectrum where space geodesy, space navigation and astronomy require the orientation of the Earth at the level of microseconds. In the middle of these, of course, is the essential need for a common world civil time scale. It is impossible to meet all these needs with just one time scale for the obvious reason that an atomic time scale is uniform while the rotation of the Earth is not. Nevertheless, the atomic time scale UTC and the time scale of the rotating Earth, UT1, must be securely linked together, which they are and will continue to be at the level of microseconds. 2. The proposal to abolish leap seconds in UTC The proposal at the International Telecommunication Union to abolish leap seconds in UTC stems essentially from two reasons: a. The great difficulty of using an atomic time scale that includes occasional but not accurately predictable one-
second steps in satellite navigation systems which has resulted in the use of different continuous atomic time scales such as GPS time and in the future Galileo time and BeiDou time. This may complicate unnecessarily not only their inter-
operability but also their reliability. b. Difficulties foreseen in ensuring the security and reliability of the increasing range of timing systems at all levels of accuracy if they have to operate in the presence of one-
second step changes. The problem of ensuring completely unambiguous time information at the instant of the step change is not easy to solve. A broad range of infrastructural systems, communications, power grids, air traffic control all depend critically on precise and reliable



Dr Felicitas Arias, Director of the BIPM Time Department


1

Among the participants from around the world were invited experts from the International Telecommunication Union and its relevant Study Groups and Working Parties, other international organizations with interests in time and frequency, astronomical organizations and observatories, satellite navigation systems, universities and national metrology institutes.


timing. The public is becoming more and more demanding as regards the safety and reliability of these systems. 3. The continued use of UTC for civil time in the absence of leap seconds Taking all this into account, we are of the opinion, and this reflects the majority view expressed at the Discussion Meeting, that if the proposal to abolish the leap second in UTC is adopted, it will continue to be legitimate in the UK, for example, or in the time zone centred on the Greenwich meridian, to represent civil time by the atomic time provided by the National Physical Laboratory, namely UTC(NPL). The additional small but, nevertheless increasing, offset that will result from the abolition of leap seconds will remain insignificant compared to the already existing annual variations in local solar time on the Greenwich meridian. These variations, which amount to plus and minus about sixteen minutes, are due to the orbit of the Earth around the Sun being an ellipse rather than a circle and to it being inclined with respect to the Equator. In addition, there exists the range of local solar times across the UK from East to West which amount to some thirty minutes. UTC will continue to be securely linked to the rotation of the Earth since difference UT1-
UTC will be available at the level of microseconds from the relevant international service. 4. Further expected improvements foreseeable for UTC Among other topics that were presented and noted by the participants were: · · · Time laboratories being equipped with better clocks; New primary frequency standards, in particular optical clocks; Improved time and frequency comparisons using fibre-
optic links and other possible solutions; Improved algorithms for time scale calculation; More frequent publication of UTC by the BIPM.

· ·

All of these taken together are expected to reduce the uncertainty of UTC from its present level of about 4 parts in 1016 to approaching 1 part in 1017, with all the advantages and possibilities that this will bring.