43rd CGSIC - Timing subcommittee 1

43rd CGSIC Meeting - Timing Session Thursday, 11 March 2004, 13:00

Chair: Włodzimierz Lewandowski, BIPM Co-Chair: Victor Zhang, NIST

13:00 Introduction _________________________ W. Lewandowski, BIPM 13:15 Report from NIST ____________________ V. Zhang, NIST 13:30 Report from USNO ___________________ D. Matsakis, F. Vannicola, USNO 13:45 Timing interoperability between GPS and Galileo ______________________________ E. Powers, USNO 14:00 Report from APL _____________________ M. Miranian, APL 14:15 Time transfer research at USNO ________ J. Brad, B. Fonville, D. Matsakis, USNO 14:30 Precise time synchronization throughout Robert A. Nelson, Satellite the solar system _______________________ Engineering Research Corporation, Bethesda, MD 14:45 Disussion 15:00 Session End

43rd CGSIC - Timing subcommittee 2

AREAS BEING SERVED

International Atomic Time (TAI) and UTC

International Timing Centers

Primary Frequency Standards

Telecommunications Industries

NASA/JPL Deep Space Network

NIST Global Time Service

Power Grids and other Industries

As Research and Comparison Tool

Other

43rd CGSIC - Timing subcommittee 3

What future for UTC ?

Włodzimierz Lewandowski Bureau International des Poids et Mesures

Sèvres

43rd CGSIC - Timing subcommittee 4

Unification of time

• October 1884 - adoption of a prime meridian and of an associated time– Greenwich meridian (origin of longitudes)– universal time, based on the rotation of the Earth

• International Astronomical Union, 1948– recommends the use of universal time (UT)

• International Astronomical Union, 1971; International Telecommunications Union; Conférence Générale des Poids et Mesures– recommend the use of coordinated universal time (UTC)

43rd CGSIC - Timing subcommittee 5

Atomic time (1971)

• Based on an atomic transition.

• Unit is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.

• The second of atomic time (SI second) is shorter in 1.4 x 10-8 s than the second of ET (averaged for year 1960).

• Clocks have no more the solely role of time keepers, they also produce the frequency that realises the second of the SI.

43rd CGSIC - Timing subcommittee 6

Coordinated Universal Time (UTC)

• UTC is the reference time scale for world wide time

coordination.

• It serves as the basis of legal times in the different countries.

• UTC is calculated at the BIPM on the basis of readings of

clocks in the national laboratories.

• Local realizations of UTC named UTC(k) are broadcast by

time signals.

43rd CGSIC - Timing subcommittee 7

Coordinated Universal Time (UTC)

• Defined to fulfil mainly the need of a time scale

somehow related to the rotation of the earth.

– The validity of this need is under discussion at present (ITU,

IAU, URSI)

• Conceptually identical to TAI but suffering from 1

second time steps (TAI - UTC = 32s today).

– The definition of UTC is under revision.

43rd CGSIC - Timing subcommittee 8

International Atomic Time (TAI)

• Uniform time scale.

• High stability in the long term(0.6 x 10-15, ~ 40 days).

• Accuracy conferred by using the reported measurements of the PFS.

• Calculated in differed time on the basis of monthly blocks of data.

43rd CGSIC - Timing subcommittee 9

[TAI - Time scale (i )]

-5

5

15

25

35

1970 1980 1990 2000 2010

Year

Tim

e di

ffere

nce

/sec

onds

UTC

GLONASS time

GPS time

TAI GALILEO time

43rd CGSIC - Timing subcommittee 10

Colloquium on the UTC Time Scale

28 - 29 May 2003

IEN Galileo Ferraris, Torino, Italy

43rd CGSIC - Timing subcommittee 11

Conclusions

1. Any change should slowly evolve from the current UTC by transition to a uniform time scale.

2. The final time scale should have a new name to distinguish it from Universal Time, since Universal Time is generally understood to be linked to Solar Time, and the earth rotation. A new name suggested was International Time, Temps International (TI).

3. A suggested date inaugurating any change would be 2022, the 50th anniversary of the UTC time scale. The date suggested was influenced by the beyond the lifetime of currently existing systems that would expensive to change.

43rd CGSIC - Timing subcommittee 12

Conclusions (cont.)

4. TI should be a continuous atomic time scale without Leap Seconds that is synchronized with UTC at the time of transition.

5. UT1 information would continue to be made available under the sole responsibility of the IERS.

43rd CGSIC - Timing subcommittee 13

MEETING ANNOUNCEMENT

_____________________________________

TAI time laboratories meeting, 31 March 2004, BIPM

CCTF, 1-2 April 2004, BIPM

EFTF, 5-8 April 2004, NPL, Teddington, UK

43rd CGSIC - Timing subcommittee 14

43rd CGSIC - Timing subcommittee 15

43rd CGSIC Meeting - Timing Session Thursday, 11 March 2004, 13:00

Chair: Włodzimierz Lewandowski, BIPM Co-Chair: Victor Zhang, NIST

13:00 Introduction _________________________ W. Lewandowski, BIPM 13:15 Report from NIST ____________________ V. Zhang, NIST 13:30 Report from USNO ___________________ D. Matsakis, F. Vannicola, USNO 13:45 Timing interoperability between GPS and Galileo ______________________________ E. Powers, USNO 14:00 Report from APL _____________________ M. Miranian, APL 14:15 Time transfer research at USNO ________ J. Brad, B. Fonville, D. Matsakis, USNO 14:30 Precise time synchronization throughout Robert A. Nelson, Satellite the solar system _______________________ Engineering Research Corporation, Bethesda, MD 14:45 Disussion 15:00 Session End