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Judah Levine (Fed)

Judah Levine joined the staff of the National Bureau of Standards (NBS) in 1969. The National Bureau of Standards was renamed the National Institute of Standards and Technology (NIST) in the 1980s, and Dr. Levine has worked in the Time and Frequency Division of NBS and NIST since 1972.

Dr. Levine is currently a Fellow of the National Institute of Standards and Technology and is the leader of the Network Synchronization Project in the Time and Frequency Division. He is also a Fellow of JILA, an institute on the campus of the University of Colorado that is operated jointly by the University of Colorado and NIST, and he is an adjoint Professor in the Department of Physics of the University.

Dr. Levine is responsible for the design and implementation of the time scales AT1 and UTC(NIST), which provide the reference signals for all of the NIST time and frequency services. He has also designed and implemented three backup time scales in Boulder: TSC, KGA, and KGC, which improve the reliability and availability of the time services. In addition to the primary time scales in Boulder, satellite time scales at the NIST/Gaithersburg facility and at NIST radio station WWV in Fort Collins, Colorado, provide the reference times for the time services at those locations. Dr. Levine steers these time scales from time to time by adjustments to the ensemble frequencies so as to maintain a close agreement between each of these time scales and the UTC time scale computed by the International Bureau of Weights and Measures (

Dr. Levine designed and built the servers that support the Automated Computer Time Service (ACTS) and the Internet Time Service, which provide time and frequency information to users in a number of different digital formats. He also developed client software for a number of common operating systems.

The ACTS service provides time information by transmissions that use dial-up telephone lines and modems, and is realized using a number of parallel computers that control a telephone rotary. The ACTS service receives about 4,000 requests per day.

The Internet Time Service uses 27 computers that are located at NIST facilities in Boulder, Fort Collins and Gaithersburg. These computers receive about one million requests per second for time stamps in 3 different standard formats. In addition to the standard formats including the Network Time Protocol (NTP), the DAYTIME format and the TIME format, the servers support digitally-signed NTP, which assures the authenticity of the information, and the UT1 data service, which provides UT1 time in NTP format, and is used by astronomers and in astronomical calculations. Dr. Levine is currently working on various techniques to improve the accuracy and availability of time signals that are traceable to national standards. (The details are in the publications list.)

In addition to supporting the time scale operations and the services described above, Dr. Levine work is focused on these areas:

  1. A study of the future of the UTC time scale and developing a consensus for a continuous UTC. This work is joint with the staff of the Time Department at the BIPM and the time services of other National Metrology Institutes.
  2. Studies of various aspects of time distribution as a member of Working Party 7A of the International telecommunications Union (ITU, This work includes the question of the future of UTC, but also includes other questions including the interference between broadcast services and wireless charging systems, the collaboration with other agencies such as the International Earth Rotation and Reference Service ( and representatives from various astronomical organizations.
  3. Work on the integrity and availability of network time services given the increasingly hostile environment of the public Internet. This work includes multi-factor authentication and other authentication techniques and improving the resistance of the time services to denial of service at other attacks.
  4. Studying and implementing methods for transmitting time and frequency information that is independent of signals from global navigation satellites (such as GPS), and which provides timing data with an accuracy of 1 microsecond or better. This work includes collaborations with various third parties to construct and test transmission links between NIST facilities and user locations that are based on optical-fiber circuits. There are currently agreements with two third parties to study this method, and links from the reference time scales both at Boulder and at Gaithersburg are currently being evaluated. There are also preliminary discussions with other users. Finally, preliminary discussions are examining the possibility of a time comparison between the various timing facility in the Washington, D.C. region by using “signals of opportunity,” such as the digital television transmissions by a local TV station.

In addition to his work on questions of time and frequency at NIST, Dr. Levine is an active faculty member in the Department of Physics of the University, and participates in various departmental activities. In addition to teaching various undergraduate classes, Dr. Levine is involved in other departmental activities:

  • Dr. Levine is a member of the committee that administers the Comprehensive Examination (Comps-II) to all second-year graduate students. In addition to the formal oral examinations, Dr. Levine acts as a mentor to women and minority students, who often have inadequate experience in oral presentations and whose performance in the comps-II format often is not an accurate evaluation of their abilities.
  • Dr. Levine is a member of the committee that organizes the “Saturday afternoon” monthly lecture series. This series presents talks by faculty members (and other professionals) on various topics in physics and related areas. It is intended for high-school students, and is widely advertised. A significant number of adult members of the community also attend regularly. The talks are presented in the Duane Physics Building of the University and are typically attended by 50 or 60 people. One of the most important aspects of the talks is the extensive question and answer period both at the end of the talk and during the refreshment period in the lobby.

Postdoctoral positions

  • NATO Postdoctoral appointment, Oxford University, UK, 1966 - 1967
  • ARPA Postdoctoral appointment, JILA, University of Colorado, 1967 - 1969

Professional society memberships

  • Fellow of the American Physical Society
  • Senior Member, Institute of Electrical and Electronic Engineers
  • Member, American Association of Physics Teachers
  • Member, Institute of Navigation


  • 5,274,545, "Device and Method for Providing Accurate Time and/or Frequency," Issued 28 December 1993. With D. W. Allan, M. Weiss and D. Davis.
  • 6,393,566, "A Time-Stamp Service for the National Information Network," issued May 12, 2002.

Selected Publications (most recent first)

  • Judah Levine, Patrizia Tavella, and Martin Milton, Towards a consensus on a continuous coordinated universal time, Metrologia, 60, 014001, 2023. doi: 10.1088/1681-7575/ac9da5.
  • P Defraigne, J Achkar, M J Coleman, M Gertsvolf, R Ichikawa, Judah Levine, P. Uhrich, P Whibberley, M Wouters and A Bauch, Achieving traceability to UTC through GNSS measurements, Metrologia, 59, 064001, 2022. doi: 10.1088/1681-7575/ac98cb.
  • Judah Levine, The Statistics of Computer Clocks and the Design of Synchronization Algorithms, J. Res. of NIST, Vol. 125, pp. 1-33.
  • J. Yao, J. A. Sherman, T. Fortier, H. Leopardi, T. Parker, W. McGrew, X. Zhang, D. Nicolodi, R. Fasano, S. Schaffer, K. Beloy, J. Savory, S. Romisch, C. Oates, S. Diddams, A. Ludlow, and J. Levine, Optical-clock-based time scale, Phys. Rev. Appl. 12 044069/1-10, 2019.
  • Demetrios Matsakis, Judah Levine, Michael A. Lombardi, Metrological and Legal Traceability of Time Signals, Inside GNSS, March/April 2019, pp. 48-58.
  • W. R. Milner, J. M. Robinson, C. J. Kennedy, T. Bothwell, D. Kedar, D. G. Matei, T. Legero, U. Sterr, F. Riehle, H. Leopardi, T. M. Fortier, J. A. Sherman, J. Levine, J. Yao, J. Ye, and E. Oelker, Demonstration of a time scale based on a stable optical carrier, Phys. Rev. Lett. 123, 173201/1-6, 2019.
  • Incorporating an Optical Clock into a time scale, J. Yao, T. Parker, N. Ashby and J. Levine, IEEE Trans. UFFC, Vol. 65, pages 127-134, 2018.
  • The Development of a new Kalman-filter time scale at NIST, Jian Yao, Thomas Parker and Judah Levine, Proc. 48th PTTI Meeting, Monterey, California, January, 2017, pages 18-25.
  • Usage Analysis of the NIST Internet Time Service, Jeff Sherman and Judah Levine, J. Res. of NIST, Vol. 121, pp. 33- 46, 2016.
  • The history of time and frequency from antiquity to the present day, Judah Levine, European Journal of Physics, Section H, Vol 41, pages 1-67, 2016.
  • Complete list of publications


  • Dean's prize in physics, Yeshiva College, June, 1960.
  • Member of Sigma Pi Sigma, Physics Honor Society.
  • Founder's Day Award, New York University, October, 1966.
  • Special Achievement Award, NBS, July, 1972.
  • Award for Special Service, (Time Scale Algorithm), NBS, August, 1978.
  • Department of Commerce Bronze Medal, 8/80. Outstanding Achievement in Precision Geophysical Measurements.
  • Award for Outstanding Achievement in Service to the Public, Denver Federal Executive Board, 6/81.
  • Department of Commerce Gold Medal, August, 1983. Outstanding achievement in the development of time-scale algorithms.
  • Allen V. Astin Measurement Science Award, December, 1998. Award for time transfer methods.
  • Elected as Fellow of NIST, March, 2004
  • Department of Commerce Gold Medal, November, 2007. Outstanding achievement in operating the NIST time scale and in providing time services. The award was shared with Tom Parker.
  • Colorado Governor’s award for research impact in information technology, February, 2009.
  • Presidential Rank Award, Distinguished Senior Professional, December, 2011.
  • Precise Time and Time Interval, Distinguished Service Medal, Presented at PTTI conference, 2012
  • I.I. Rabi Award, IEEE Ultrasonics, Ferroelectrics and Frequency Control Society, 2013.
  • Department of Commerce Silver Medal, November 2018. Outstanding achievement in new time services.
  • Department of Commerce Silver Medal, February, 2023. Providing Time services that do not depend on signals from Global Navigation Satellites, responding to Executive Order 13905. Shared with multiple recipients.


A Resilient Architecture for the Realization and Distribution of Coordinated Universal Time to Critical Infrastructure Systems in the United States: Methodologies and Recommendations from the National Institute of Standards and Technology (NIST)

Jeffrey Sherman, Ladan Arissian, Roger Brown, Matthew J. Deutch, Elizabeth Donley, Vladislav Gerginov, Judah Levine, Glenn Nelson, Andrew Novick, Bijunath Patla, Tom Parker, Benjamin Stuhl, Jian Yao, William Yates, Michael A. Lombardi, Victor Zhang, Douglas Sutton
The Time and Frequency Division of the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce (DOC), was

Distributing Time and Frequency Information

Judah Levine
This chapter discusses the statistics that are used to characterize the performance of clocks, oscillators, and the networks that are used to calibrate and

Optical-Clock-Based Time Scale

Jian Yao, Jeffrey A. Sherman, Tara M. Fortier, Andrew D. Ludlow, Holly Leopardi, Thomas E. Parker, William F. McGrew, Scott A. Diddams, Judah Levine
A time scale is a procedure for accurately and continuously marking the passage of time. It is exemplified by coordinated universal time (UTC), and provides the

Metrological and legal traceability of time signals

Michael A. Lombardi, Demetrios Matsakis, Judah Levine
Metrological traceability requires an unbroken chain of calibrations that relate to a reference, with each calibration having a documented measurement
Created February 20, 2019, Updated April 10, 2023