23ème Conférence générale des poids et mesures Rapport du Comité Consultatif

23ème Conférence générale des poids et mesuresParis, 12-16 novembre 2007

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23ème Conférence générale des poids et mesures

Rapport du Comité Consultatif du Temps et des Fréquences

Luc ERARDPrésident du CCTF


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Sommaire

• TAI/UTC• Comparaisons d’horloges• Comparaisons clés (KC) • Groupes de travail (WG)• Développements futurs


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International time scales TAI and UTC• The BIPM is responsible for realizing, maintaining and disseminating the

international reference time scales;

• International time keeping is the result of the cooperation of many laboratories distributed worldwide;

• The efforts of the community dealing with time metrology are focused towards the construction of time scales adapted to the most demanding applications and requiring:– Continuity– Reliability– Accessibility– Frequency stability of order 10-15

– Frequency accuracy of order 10-15 (traceability to the SI second)


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International time scales TAI and UTCTAI

Atomic scale (14th CGPM,1971), ContinuousCalculated in post-real time (~10 days after the last

date of data), Frequency stability (0.5 x 10-15 @40 days)

Unit: SI second, Frequency accuracy (~10-15) It has no representations through clocks, not

disseminated It has scientific applications and provides a

frequency reference


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International time scales TAI and UTCUTC (coordinated universal-time)

Atomic time scale (ITU-R, Rec. 460, 1970; 460-1, 1974) Continuous with one-second steps at irregular intervals

(leap second) Differs from TAI in an integer number of seconds (33 s at

present) Post-processed (~10 days after last date of data) Unit: SI second, Frequency stability and accuracy (idem

TAI) Represented by clocks

Local approximations UTC(k), [UTC-UTC(k)] < 100 ns (recomm.)

Disseminated Circular T, CCTF-K001.UTC (delayed time), Time signals (real

time approximations) Legal applications

Basis of legal times


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TAI/UTC ALGOS (algorithm for calculation)

Time and frequency differences

Clock data Time transferdata

EAL •Optimized frequency stability

•No constrained to be accurate in frequency

PFS data Frequency corrections

+

TAI + (-n x s) UTC

•Optimized frequency stability

•Accurate in frequencyIERS leap second announcements


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PRIMARY FREQUENCY STANDARDS (PFS)

• 11 regularly reporting measurements to BIPM – from 6 time National metrology

laboratories• 7 are Caesium fountains

– frequency accuracy 0.5 to 4 × 10-15

• improve the accuracy of the TAI


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Typical characteristics of the calibrations of the TAI frequency provided by the different primary

standards in 2006 Primary Standard

Type /selection

Type B std. Uncertainty

Operation Comparison with

Number/typical duration of comp.

IT-CSF1 Fountain (0.5 to 0.8)x10-15

Discontinuous H maser 3 / 20 to 35 d

NICT-O1 Beam /Opt.

6x10-15 Discontinuous UTC(NICT) 2 / 20 to 30 d

NIST-F1 Fountain

0.3x10-15 Discontinuous H maser 3 / 30 to 40 d

NMIJ-F1 Fountain

4x10-15 Discontinuous H maser 3 / 10 to 15 d

PTB-CS1 Beam /Mag.

8x10-15 Continuous TAI 12 / 30 d

PTB-CS2 Beam /Mag.

12x10-15 Continuous TAI 12 / 30 d

PTB-CSF1 Fountain


SYRTE-FO1 Fountain

0.4x10-15 Discontinuous H maser 2 / 15 d

SYRTE-FO2 Fountain


SYRTE-FOM Fountain

1.2x10-15 Discontinuous H maser 1 / 15 d

SYRTE-JPO Beam /Opt.

6x10-15 Discontinuous H maser 11 / 20 to 30 d

Reports of operation of PFS are regularly published in the BIPM Annual Report


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Improvements in the algorithm• Model of instability of EAL

– is used to include PFS calibrations in a month of calculation of Circular T

– normalized filter coefficients (“weights”) that depend on

• uncertainty of the PFS evaluation• distance between the intervals of evaluation and

calculation• instability of EAL

• Need of a refined model (Arias&Petit, 2005)– negative filter coefficients– stability of PFS better than that of EAL

• New model adopted since 2005.7


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Improvements in the algorithmEAL stability models

1.E-16

1.E-15

1.E-14

10 100 1000t / day

sy(t

)

Until 2005.7 Since 2005.7


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Comparaisons clés (KC)• CCTF-K001.UTC

– Published since January 2005– Reference value is UTC– Updated monthly

• CCTF-K002.FREQ– Under construction – Coordination between CCTF WG on the MRA

and the BIPM


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CCTF-K001.UTC Calculation of UTCDegrees of equivalence: [UTC - UTC (k )] and its expanded uncertainty (U k = 2u k )

Computed values for 26 September 2007 at 0h UTC, MJD = 54369

-140

-120

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

140

NM

IAB

EV

BIM

Bel

GIM

ME

TAS

CE

NA

MC

EN

AM

EP

EIM

INR

IM JVK

RIS

SV

MT/

PFI

LNM

CM

IKE

SM

KE

HM

SL

NIC

TN

IMIN

M(R

O)

NIM

TN

ISN

IST

NM

IJN

ML-

SIR

IMN

PL

NP

LIN

RC

OP

GU

MP

TBR

OA

SC

LS

PR

ING

Sin

gapo

reM

IRS

/SIQ

SM

US

PV

NIIF

TRI

UD

EC TL IPE

UM

EN

Mi-V

SL

DM

DM

[UTC

- U

TC(k

)] (m

odul

o 10

0 ns

) /

ns


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Groupes de travail (WG)

• WG on TAI– Symposium on time scales algorithms

in 2008 (San Fernando)– GPS CV to AV (with a pivot laboratory)

• WG on Global navigation satellite system: means of implementing the use of carrier phase for time and frequency transfer in TAI


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• WG on TWSTFT:– Negociation of links with Intelsat

• WG on Coordination of the Development of Advanced Time and Frequency Transfer Techniques

• WG on Primary frequency standard: – Workshop in Geneva, 2007


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• CCL/CCTF WG on frequency standards:– Proposal for radiations suitable for

secondary representations of the second;

– Proposal for radiations for the practical realization of the meter;

> Single list of radiations• WG on CIPM MRA: still missing

representatives of RMOs


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Développements futurs

Improvement of the time scales

– Better clocks: commercial and PFS, frequency prediction, clock weighing procedure,…

– Clock comparison: less noisy techniques, accurate frequency transfer techniques GPS, TWTSTF, Galileo, ...


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Gill & Riehle 2006

Développements futursOptical clocks


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Développements futurs

• Comb technology for frequency comparisons (microwave to optical);

• Optical fiber links for comparison;• Use of secondary representation of

the second for TAI;• Redefinition of the second??

Documents

23ème Conférence générale des poids et mesures Rapport du Comité Consultatif