NIST TIME AND FREQUENCY BULLETIN NISTIR 6604-1 NO. 518 JANUARY 2001 1. GENERAL BACKGROUND INFORMATION 2 2. TIME SCALE INFORMATION 2 3. PHASE DEVIATIONS FOR WWVB AND LORAN-C 4 4. BROADCAST OUTAGES OVER FIVE MINUTES AND WWVB PHASE PERTURBATIONS 5 5. NOTES ON NIST TIME SCALES AND PRIMARY STANDARDS 5 6. BIBLIOGRAPHY 5 7. SPECIAL ANNOUNCEMENTS 7 This bulletin is published monthly. Address correspondence to: Gwen E. Bennett, Editor Time and Frequency Division National Institute of Standards and Technology 325 Broadway Boulder, CO 80303-3328 (303) 497-3295 Email: bennett(5)boulder.nist.gov NOTE TO SUBSCRIBERS: Please include your address label (or a copy) with any correspondence regarding this bulletin. U.S. DEPARTMENT OF COMMERCE, Norman Y. Mineta, Secretary TECHNOLOGY ADMINISTRATION, Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, Karen H. Brown, Acting Director -1- . 1. GENERAL BACKGROUND INFORMATION ABBREVIATIONS AND ACRONYMS USED IN THIS BULLETIN BIPM - Bureau International des Poids et Mesures CCIR - International Radio Consultative Committee Cs - Cesium standard GOES - Geostationary Operational Environmental Satellite GPS - Global Positioning System lERS - International Earth Rotation Service LORAN - Long Range Navigation MC - Master Clock MJD - Modified Julian Date NVLAP - National Voluntary Laboratory Accreditation Program NIST - National institute of Standards and Technology NOAA - National Oceanic and Atmospheric Administration ns - nanosecond SI - International System of Units JJS - microsecond TA - Atomic Time ms - millisecond TA! - International Atomic Time s - second USNO - United States Naval Observatory min - minute UTC - Coordinated Universal Time VLF - very low frequency 2. TIME SCALE INFORMATION The values listed below are based on data from the lERS, the USNO, and NIST. The UTC(USNO,MC) - UTC(NIST) values are averaged measurements from up to 10 GPS satellites (see bibliography on page 5). UTC-UTC(NIST) data are on page 3. 0000 HOURS COORDINATED UNIVERSAL TIME DEC 2000 MJD UTI-UTC(NIST) UTC(USNO,MC)-UTC(NIST) ±5 ms) ±20 ns) ( ( 7 51885 ±111 ms -4 ns 14 51892 +"^04 ms 4 ns 21 51899 ± 98 ms 9 ns 28 51906 ± 95 ms 3 ns The master clock pulses used by the WWV, WWVH, WWVB, and GOES time code transmissions are referenced to the UTC(NIST) time scale. Occasionally, 1 s is added to the UTC time scale. This second is called a leap second. Its purpose is to keep the UTC time scale within ±0.9 s of the UT1 astronomical time scale, which changes slightly due to variations in the rotation of the Earth. NOTE: No positive leap second will be inserted at the end of December 2000. Positive leap seconds, beginning at 23 h 59 min 60 s UTC and ending at O h O min 0 s UTC, were inserted in the UTC timescale on 30 June 1972, 1981-1983, 1985, 1992, 1993, 1994, and 1997, and on 31 December 1972-1979, 1987, 1989, 1990,1 995, and 1998. There have been 22 leap seconds in total. The use of leap seconds ensures that UT1 - UTC will always be held within ±0.9 s. The current value of UT1 - UTC is called the DUT1 correction. DUT1 corrections are broadcast by WWV, WWVH, WWVB, and GOES and are printed below. These corrections may be added to received UTC time signals in order to obtain UT1 ±0.3s beginning 0000 UTC 06 January 1999 DUT1 = UT1 - UTC = ±0.2s beginning 0000 UTC 13 April 2000 +0.1s beginning 0000 UTC 19 October 2000 -2- j ThedeviationofUTC(NIST) fromUTChasbeenwithin +/-100 ns sinceJuly 6, 1994. The tablebelow shows values ofUTC UTC(NIST) assuppliedby theBIPM intheirCircularTpublicationforthemostrecent 350dayperiod inwhichdataareavailable Data are givenat tenday intervals. Five day interval dataare available inCircular T. 0000 Hours Coordinated Universal Time DATE MJD UTC-UTC(NIST) ns Dec 17, 1999 51529 -5 Dec 27, 1999 51539 -3 , Jan 6, 2000 51549 0 Jan 16, 2000 51559 2 Jan 26, 2000 51569 0 Feb 5, 2000 51579 6 Feb 15, 2000 51589 5 Feb 25, 2000 51599 7 Mar 6, 2000 51609 8 Mar 16, 2000 51619 15 Mar 26, 2000 51629 15 Apr 5, 2000 51639 20 Apr 15, 2000 51649 20 Apr 25, 2000 51659 17 May 5, 2000 51669 ~ 17 r May 15, 2000 , ( 1 51679- ; 17 May 25, 2000 51689 18 June 4, 2000 51699 18 June 14, 2000 51709 -p. 20 , June 24, 2000 51719 23 July 4, 2000 51729 24 July 14, 2000 51739 24 July 24, 2000 51749 24 Aug 3, 2000 51759 26 Aug 13, 2000 51769 25 Aug 23, 2000 51779 22 Sep 2, 2000 51789 12 Sep 12, 2000 51799 6 Sep 22, 2000 51809 0 Oct. 2, 2000 51819 -8 Oct. 12, 2000 51829 -13 Oct. 22, 2000 51839 -19 Nov. 1, 2000 51849 -25 Nov. 11, 2000 51859 -22 Nov. 21, 2000 51869 -21 -3- 3. PHASE DEVIATIONS FOR WWVB AND LORAN-C WWVB - The values shown for WWVB are the time differences between the time markers of the UTC(NIST) time scale and the first positive-going zero voltage crossover measured at the transmitting antenna. The uncertainty of the individual measurements is +0.5/js. The values listed are for 1300 UTC. LORAN-C - The values shown for Loran-C represent the daily accumulated phase shift (in ns). The phase shif^ measured by comparing the output of a Loran receiver to the UTC(NIST) time scale for a period of 24 h. If data were not recorded on a particular day, the symbol (-) is printed. The master stations monitored are Dana, IN (8970) and Fallon, NV (9940). The monitoring is done from the NIST laboratories in Boulder, Colorado. Note: The values shown for Loran-C are in nanoseconds. UTC(NIST)-WWVB (60 kHz) UTC(NIST) - LORAN PHASE (ns) ANTENNA PHASE LORAN-C (DANA) LORAN-C (FALLON) DATE MJD (as) (8970) (9940) 12/01/00 51879 5.61 (-) (-) 12/02/00 51880 5.61 (-) (-) 12/03/00 51881 5.60 -42 -238 12/04/00 51882 5.59 -1 -258 12/05/00 51883 5.61 -594 -260 12/06/00 51884 5.58 -181 -167 12/07/00 51885 5.58 +273 -244 12/08/00 51886 5.58 +419 -36 12/09/00 51887 5.58 +452 +500 12/10/00 51888 ,5,58 -450 -222 12/11/00 51889 5.58 +572 -616 12/12/00 51890 5.57 +416 +292 12/13/00 51891 5.56 -18 -496 12/14/00 51892 5.55 -6 -83 12/15/00 51893 5.55 -177 -233 12/16/00 51894 5.56 +316 -624 12/17/00 51895 5.56 -274 -177 12/18/00 51896 5.56 -244 +33 12/19/00 51897 5.56 +463 -443 12/20/00 51898 5.55 -242 -427 12/21/00 51899 5.55 -393 -287 12/22/00 51900 5.57 +49 +2 12/23/00 51901 5.57 +345 +105 12/24/00 51902 5.57 +419 -291 12/25/00 51903 5.57 +85 -123 12/26/00 51904 5.56 +125 +156 12/27/00 51905 5.55 -533 +444 12/28/00 51906 5.55 +509 (-) 12/29/00 51907 5.55 +365 +152 12/30/00 51908 5.55 +29 +157 12/31/00 51909 5.55 +89 -29 -4- 1 4. BROADCAST OUTAGES AND WWVB PHASE PERTURBATIONS OUTAGES OF 5 MINUTES OR MORE PHASE PERTURBATIONS WWVB 60 kHz Station DEC MJD Began Ended Freq. DEC MJD Began End 2000 UTC UTC 2000 UTC UTC WWVB WWV WWVH 5. NOTES ON NISTTIME SCALE AND PRIMARY STANDARDS Primaryfrequency standardsdeveloped and maintained by NISTare used to provide accuracy (rate) inputto the BIPM. NIST-7, which has served asthe U.S. primary standard since 1994 is being replaced by NIST-F1, a cesium fountain frequency standard. The uncertainty ofthe new standard is currently 1.7 parts in 10^^. TheAT1 scale is run in real time using datafrom an ensemble ofcesium standards and hydrogen masers. It is a free-running scalewhose frequency is maintained as constant as possible by choosing the optimum weightforeach clock thatcontributesto the computation. UTC(NIST) is generated as an offsetfrom ourreal-time scale ATI. It is steered in frequencytowards UTC using data published by the BIPM in its CircularT. Changes in the steering frequencywill be made, ifnecessary, at0000 UTC on thefirst day ofthe month, and very occasionally at mid-month. A change in frequency is limited to no more than ± 2ns/day. The frequency of UTC(NIST) is kept as stable as possible atothertimes. UTC is generated atthe BIPM using a post-processedtime-scale algorithm and is notavailable in real-time. The parametersthat we useto generate UTC(NIST) in real-time aretherefore based on an extrapolation of UTC fromthe most recent data available. BIBLIOGRAPHY 6. Allan, D.W.; Hellwig, H.; and Glaze, D.J., "An accuracy algorithm foran atomictime scale," Metrologia, Vol.11, No.3, pp.133-138 (September 1975). Allan, D.W. and Weiss, M.A., "Accurate time and frequencytransferduring common view ofa GPS satellite," Proc. 34th Annual Symposium on Frequency Control, p.334 (1980). Allan, D.W. and Barnes, J.A., "Optimal time and frequency using GPS signals," Proc. 36th Annual Symposium on Frequency Control, p.378 (1982). Drullinger, R.E.; Glaze, D.J.; Lowe, J.P.; and Shirley, J.H., "The NIST optically pumped cesium frequency standard," IEEE Trans. Instrum. Meas., IM-40, 162-164 (1991). Glaze, D.J.; Hellwig, H.; Allan, D.W.; and Jarvis, S., "NBS-4 and NBS-6; The NIST primaryfrequency standards," Metrologia, Vol.13, pp.17-28 (1977). Wineland, D.J.; Allan, D.W.; Glaze, D.J.; Hellwig, H.; and Jarvis, S., "Results on limitations in primary cesium standard operation," IEEE Trans. Instrum. Meas., IM-25, pp.453-458 (December 1976). -5- . Table 7.1 is a list of the parameters that are used to define UTC(NIST) with respect to our real-time scale ATI To find the . value of UTC(NIST) - ATI at any time T (expressed as a Modified Julian Day, including a fraction if needed), the appropriate equation to use is the one for which the desired T is greater than or equal to the entry in the Tq column and less than the entry in the last column. The values of Xi^, x, and y for that month are then used in the equation below to find the desired value. The parameters x and y represent the offset in time and in frequency, respectively, between UTC(NIST) and ATI; the parameter Xi^ is the number of leap seconds applied to both UTC(NIST) and UTC as specified by the lERS. Leap seconds are not applied to ATI Table 7.1 UTC(NIST) - ATI = x,3 4- X + y(T - To) Month X|s X y To Valid until 0000 on: (S) (ns) (ns/day) (MJD) (MJD) May 99 -32 -190383 -41.0 51299 51330 Jun 99 -32 -191654 -41.0 51330 51360 Jul 99 -32 -192884 -41 .0 51360 51391 Aug 99 -32 -194155 -41.0 51391 51422 Sep 99 -32 -195426 -40.5 51422 51452 Oct 99 -32 -196641 -40.5 51452 51483 Nov 99 -32 -197896.5 -40.0 51483 51513 Dec 99t -32 -199096.5 -40.0 51513 51533 Dec 99 -32 -199896.5 -41 .0 51533 51544 Jan 00 -32 -200347.5 -40.5 51544 51575 Feb 00 -32 -201603 -40.5 51575 51604 Mar 00 -32 -202777.5 -40.5 51604 51635 Apr 00 -32 -204033 -40.5 51635 51665 May 00 -32 -205248 -40.25 51665 51696 Jun 00 -32 -206495.75 -40.25 51696 51725'' Jul 00 -32 -207663 -40.0 51725'^ 51757 Aug 00 -32 -208943 -39.5 51757 51788 Sep 00 -32 -210167.5 -39.0 51788 51818 Oct 00 -32 -211337.5 -39.0 51818 51849 Nov 00 -32 -212546.5 -40.0 51849 51879 Dec 00 -32 -213746.5 -40.0 51879 51910 Jan 01 -32 -214986.5 -40.0 51910 51941 Feb 01 -32 -216226.5 -40.0* 51941 51969 t Rate change in mid-month Rate change one day early *Provisional rate -6- 7. SPECIAL ANNOUNCEMENTS TRACEABLE FREQUENCY CALIBRATIONS (Now NVLAP Certified) Laboratories needing traceable frequency calibrations can get them by subscribing to the NIST Frequency Measurement and Analysis Service. This service is offered on a lease basis by NIST to provide an easy and inexpensive means to obtain traceability of a laboratory frequency standard and, in addition, to calibrate other devices in the lab. This service has been designed for ease of operation and as a practical calibration tool. All necessary hardware and software is provided by NIST. Users must provide their own oscillator(s) and an ordinary telephone line so that NIST can access the system by modem. A total of five oscillators can be calibrated at the same time. Radio signals from GPS satellites are used and the measurement uncertainty is ±2 X 10'^^ per day. Any frequency from 1 Hz to 120 MHz can be measured in 1 Hz increments. The calibration data are displayed in color and a graph is plotted daily for each oscillator. Data are also stored on disk. The user can call up any of the data and view them onscreen or in the form of plots. Up to 5 months of data can be plotted on one graph. The system plots are easy to read and understand. The system manual is written clearly and the NIST staff is available by telephone to assist. The modem connection allows NIST to access the data and to prepare a monthly traceability report, which is mailed to the user. Frequency sources of any accuracy can be calibrated. The FMAS is particularly useful at the highest levels of performance. This is because each user ofthe system contributes information and calibration data forthe others. If an uncertainty arises, it is possible for NIST to call by modem to another user nearby. In this way problems in data interpretation can be resolved. NVLAP certification requirements for frequency measurement are met by following the NIST-FMAS operating manual. This service does not eliminate the NVLAP audits but, when installed and operated per the NIST guidelines, audit requirements are easily met. NIST retains title to the equipment and supplies. All necessary replacement parts are replaced by overnight shipment. Training for use of the system is available if requested by the user. The NIST Frequency Measurement and Analysis Service provides a complete solution to nearly all frequency measurement and calibration problems. For a free information package, please contact Michael Lombardi at (303) 497-3212, E-mail at lombardi(3lboulder.nist.gov, or write to; Michael Lombardi, NIST, Division 847, 325 Broadway, Boulder, CO 80303. IMPORTANT NOTICE! The Time and Frequency Bulletin data are now online at www.boulder.nist gov/timefreq/ . -7- 1 AN EQUAL OPPORTUNITY EMPLOYER NIST TIME AND FREQUENCY BULLETIN NISTIR 6604-1 NO. 518 JANUARY 2001 U.S. Department ofCommerce Technology Administration National Institute ofStandards and Technology FIRST-CLASS MAIL Time and Frequency Division POSTAGE & FEES PAID Boulder, Colorado 80303-3328 NIST Permit No. G195 OFFICIAL BUSINESS Penalty for Private Use, $300 GWENBENNETT DIVISION847 COPY 1 NIST 325BROADWAY BOULDER,CO80303