Local time scale at PTB UTC(PTB) Ali Al-masoudi, Stephan Falke, Sebastian Häfner, Stefan Vogt, Christian Lisdat

Outline Time scales History of atomic clock at PTB Local time scale UTC(PTB) Time transfer International time comparsions Seite 2 von 23

The time scales A number of different time scales are current use, Dynamic time scales Dynamic time scale is derived from a description of a dynamical physical system where the time t is used as a parameter to describe the evolution of the system Universal time (UT) based on the rotation of the Earth around its polar axis, Ephemeris time (ET) based on the rotation of the Earth around the sun, Integrated time scales Integrated time scale is based on a time interval e.g. the second as derived from the frequency of the transition in 133 Cs International Atomic Time (TAI) Coordinated Universal Time (UTC) Atomic clocks an integral number of seconds F. Riehle, Frequency Standards (2004) Seite 3 von 23

T(s) The time scales The starting point of TAI was fixed such that on January 1, 1958, at 0:00 TAI approximately agreed with the corresponding instant of the astronomical time scale UT TAI 0 UT TAI UT 1958-20 -40 1958 1972 2012 Seite 4 von 23

T(s) The time scales The starting point of TAI was fixed such that on January 1, 1958, at 0:00 TAI approximately agreed with the corresponding instant of the astronomical time scale UT 0 10s UT TAI TAI UT+10s 1972-20 -40 1958 1972 2012 Seite 5 von 23

T(s) The time scales The starting point of TAI was fixed such that on January 1, 1958, at 0:00 TAI approximately agreed with the corresponding instant of the astronomical time scale UT 0 TAI 10s UTC UT TAI UT+10s 1972-20 -40 1958 1972 2012 Seite 6 von 23

T(s) The time scales The starting point of TAI was fixed such that on January 1, 1958, at 0:00 TAI approximately agreed with the corresponding instant of the astronomical time scale UT 0 TAI 35s TAI UT+35s 2012 No leap second 2013-20 UTC UT International Earth Rotation and Reference System Service (IERS) -40 1958 1972 2012 Seite 7 von 23

The time scale UTC The time scale UTC (Coordinated Universal Time) serves as a worldwide reference time scale for the determination of time in everyday life and in scientific and technical fields such as astronomy, geodetic surveying, navigation and telecommunication. UTC is realised by the joint effort of more than 70 time institutes based in many countries. These institutes have about 400 atomic clocks. BIPM In Paris coordinates the acitvities of these institutes and the dissemination of UTC. The individual time institutes such as PTB use atomic clocks to realize a local time scale - in our case referred to as UTC(PTB). Which is kept in as good agreement with UTC as possible. In 2012, the difference between UTC and UTC(PTB) has always been less than 10 ns Seite 8 von 23

General scheme of the formation of UTC and TAI Corrections to local UTC (k) Leap seconds Steering of the duration of the scale unit of TAI F. Riehle, Frequency Standards (2004) Seite 9 von 23

Brief history of the atomic clock at PTB January 1959 Official start of the emission of the time signals via the transmitter DCF77 (second defined on an astronomical basis) March 1967 International redefinition of the second 1969 The atomic clock CS1 becomes operational 1978 With the Time Act of July 1978, PTB becomes responsible for legal time 1985 The atomic clock CS2 becomes operational 1988-92 Two more atomic clock (CS3 and CS4) become operational. 1999 Caesium fountain CSF1 becomes operational 2004 Caesium fountain CSF2 becomes operational. today All these atomic clocks except CS4 are still operating. They contribute substantially to the making of International Atomic Time. Seite 12 von 23

Local time scale UTC(PTB) The realization of the atomic time scale UTC(PTB) is done at PTB for several purposes UTC(PTB) serves as the reference for legal time in Germany, It serves as the reference for all internal clocks comparisons, UTC(PTB) clock(i) PTB so that PTB s clocks can contribute to the construction of the free atomic scale (EAL) by BIPM, International time comparisons, most of the time scale comparisons are done between UTC(PTB) and equivalent time scales of other institutes. For example more than ten years PTB has served as the BIPM pivot laboratory for GPS Common View time comparisons and Two-Way Satellite Time and Frequency Transfer (TWSTFT) in Europe and between Europe and the USA. Seite 13 von 23

Local time scale UTC(PTB) 5MHz phase micro-stepper (PMS) 5MHz UTC(PTB) 1PPS The PMS allows the introduction of a fractional frequency offset between the input and the output 5 MHz signals with a resolution of 6 10 17 Seite 14 von 23

Local time scale UTC(PTB) 5MHz phase micro-stepper (PMS) Standard Frequency For almost 20 years UTC(PTB) used to have its physical representation as standard frequency and one pulse per second (1PPS) signals based on is thermal beam primary clock CS2. Since February 2010 UTC(PTB) has instead been realized using an active hydrogen maser (AHM) 5MHz UTC(PTB) 1PPS The PMS allows the introduction of a fractional frequency offset between the input and the output 5 MHz signals with a resolution of 6 10 17 Time institutes usually operate several such clocks to avoid any interruption of the continuous realization of their time scales. Seite 15 von 23

Local time scale UTC(PTB) AHM 5MHz UTC(PTB) 5MHz 1PPS AHM 5MHz UTC(PTB) A. Bauch et al. Metrologia 49 (2012) 180 188 Seite 16 von 23

Local time scale UTC(PTB) A. Bauch et al. Metrologia 49 (2012) 180 188 Seite 17 von 23

Seite 18 von 23 Time Transfer Two-Way Satellite Time and Frequency Transfer (TWSTFT) The TWSTFT technique provides stable and accurate time transfer since nearly all of the propagation delay cancels out due to symmetry A B B A A t t T B A A B B t t T R 2 A t B t T 2 ) ( ) ( down A up B down B up A 2 A B B A 2 ) ( ) ( R B T B R A T A

TWSFTF and GPS sensitivity Type Time stability 24 hours Time accuracy 24 hours Frequency accuracy 24 hours GPS Direct Broadcast 2ns 3 to 10 ns 4 x 10-14 GPS Common View 1ns 1 to 5 ns 2x 10-14 GPS carrier Phase 0.1ns 1 to 3 ns 2x 10-15 TWSTFT 0.1 to 0.2 ns 1ns 2-4 x 10-15 Seite 19 von 23

International Time Comparisons Seite 20 von 23

International Time Comparisons Red INRiM Turin Blue (PTB) Cyan (NPL) Green (METES) Open circles(unso) Full circles (PTB) Crosses (SU) Triangles (NIST) Seite 21 von 23

Uncertainties of [UTC- UTC(k)] values u A Statistical component of the uncertainty u B Systematic component u Combined uncertainty Seite 22 von 23

Thank you for your attention! Physikalisch-Technische Bundesanstalt Braunschweig und Berlin Bundesallee 100 38116 Braunschweig Ali Al-masoudi Arbeitsgruppe 4.32, Optische Gitteruhren Telefon: 0531 592-4315 E-Mail: ali.al-masoudi@ptb.de www.ptb.de Stand: 01/14