9:00 a.m. - 10:00 a.m.	Reference Time Scales and Traceability Concepts	Dr. Elisa Felicitas Arias and Dr. Demetrios Matsakis
10:00 a.m. - 11:00 a.m.	Measuring Electronic and Vibration-Induced Phase Noise in Oscillators	Dr. Archita Hati
11:15 a.m. - 12:15 p.m.	Introduction to Atomic Frequency Standards	Dr. Robert Tjoelker
1:30 p.m. - 2:30 p.m.	Global Navigation Satellite Systems (GNSS)	Dr. Pascale Defraigne
2:30 p.m. - 3:30 p.m.	Fiber Based Time and Frequency Transfer	Dr. Sven-Christian Ebenhag
3:45 p.m. - 4:45 p.m.	Earth's Time Varying Rotation	Dr. Richard Gross

Reference Time Scales and Traceability Concepts

Time: Monday, January 30, 9:00 a.m. - 10:00 a.m.
Room: Spyglass

Reference time scales are maintained based on international cooperation coordinated by the International Bureau of Weights and Measures (BIPM). Algorithms for achieving the required frequency stability and accuracy are developed for supporting their construction. Time and frequency time transfer methods are used for the integration of the data into the algorithms.

National laboratories maintaining local representations of the reference time scale must fulfill the criteria of traceability to the reference. Similarly, the provision of time and frequency services needs to demonstrate that they are traceable to the time references.

This tutorial will present the concepts underlying the construction of a time scale in general, and in particular those for the computation of the reference time scale Coordinated Universal Time (UTC). Time services are been developed for disseminating time to users. For claiming that they provide reference time, they must prove that they are traceable to UTC. The concepts of traceability will be introduced and the different ways of obtaining traceability will be described.

Dr. Felicitas Arias was born in Argentina. She received the master’s degree in astronomy from the University of La Plata (Argentina) and the PhD in astrometry, celestial mechanics and geodesy from Paris Observatory. She was director of the Buenos Aires Naval Observatory and is Professor at the University of La Plata. Since 1999 she is the Director of the Time Department at the International Bureau of Weights and Measures (BIPM), where she is responsible for the maintenance of the Coordinated Universal Time (UTC). Her fields of activity are the space and time references. She is an active member of scientific organizations and unions such as the International Astronomical Union, the International Association for Geodesy, the International Earth Rotation and Reference Systems Service. She is the BIPM representative at the International Telecommunication Union. In France, she is a corresponding member at the Bureau of Longitudes. She is author of about 130 publications in scientific journals and proceedings.

Dr. Demetrios Matsakis holds a PhD from U.C. Berkeley. Initially a radio astronomer, he is now chief scientist for Time Services at the U.S. Naval Observatory. He has published over 100 papers and for almost thirty years been active in most aspects of timekeeping, including clock development, timekeeping statistics, timescale theory, time transfer, and eighteen years managing the USNO's Time Service Department. In the course of this time he has served on many international bodies and working groups, such as serving as president of the IAU's Time Commission and vice president of the U.S. delegation of the ITU's WPA.

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Measuring Electronic and Vibration-Induced Phase Noise in Oscillators

Time: Monday, January 30, 10:00 a.m. - 11:00 a.m.
Room: Spyglass

Noise, present everywhere, causes a signal source to deviate from its ideal performance. This noise introduces time dependent phase and amplitude fluctuations on the signal. The spectral purity of a frequency source can be characterized in terms of amplitude modulation (AM) and phase modulation (PM) noise. This tutorial will cover the basic theory of modulation noise, the origin of different noise types, and the effects of signal manipulation such as amplification, frequency translation, and multiplication on the spectral purity of a signal. Various phase noise measurement techniques will be discussed, in particular, the advantages and problems of the cross-spectrum technique. In addition, in this tutorial we will discuss vibration-induced phase noise. An oscillator can often provide sufficiently low intrinsic phase noise to satisfy a particular system’s requirements in a quiet environment. However, field environments are often far more strenuous than a laboratory setting; the mechanical vibration and acceleration onboard a vehicle or aircraft can introduce mechanical deformations that deteriorate the oscillator’s otherwise low PM noise. We will discuss various sources of vibration-induced phase noise, the vibration sensitivity of different classes of oscillator, and a few techniques to improve the vibration-sensitivity of an oscillator.

Archita Hati is an electronics engineer at the Time and Frequency Division of the National Institute of Standards and Technology. She received her M.Sc and Ph.D degrees in Physics from University of Burdwan, W.B., India, in 1992 and 2001 respectively. Her current field of research includes phase noise metrology, ultra-low noise frequency synthesis, development of low noise microwave and opto-electronic oscillators, and vibration analysis. She is the calibration service leader for the Time and Frequency Metrology Group at NIST. In 2015 she was awarded the Allen V. Astin Measurement Science Award for developing a world-leading program of research and measurement services in phase noise.

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Introduction to Atomic Frequency Standards

Time: Monday, January 30, 11:15 a.m. - 12:15 p.m.
Room: Spyglass

Atomic frequency standards form the basis of the definition of the second, enable ultra-stable timekeeping and timescales, and provide frequency metrology and references for a multitude of earth and space based applications that include fundamental physics, telecommunication, navigation, and radio science. There are many types of atomic frequency standards and clocks to address a wide range of application specific performance and operability requirements. Depending on the approach, achievable frequency standard accuracy, stability, size/mass/power, and cost can vary by many orders of magnitude. This course will present the fundamentals behind atomic frequency standards and survey the range of approaches.

Dr. Robert Tjoelker received degrees in architecture, mathematics, and physics from the University of Washington and the PhD degree in physics from Harvard University for the confinement and cooling of antiprotons in an ion trap and a precision comparison of the antiproton and proton mass. He currently leads the Frequency and Timing Advanced Development Group at the NASA Jet Propulsion Laboratory with responsibility for atomic frequency standard and timing developments for ground and spaceflight applications, the NASA Deep Space Network (DSN) Frequency and Timing System, and the JPL Frequency Standards Test Laboratory. He has published more than 100 journal and conference papers in the areas of atomic physics, fundamental constants, precision trapped ion mass spectrometry, atomic frequency standards, and frequency and timing technologies and systems. Dr. Tjoelker is a member of the IEEE UFFC, the American Physical Society, the Institute of Navigation, and the International Telecommunication Union USWP-7A.

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Global Navigation Satellite Systems (GNSS)

Time: Monday, January 30, 1:30 p.m. - 2:30 p.m.
Room: Spyglass

GNSS and Time have a bi-directional relationship. On the one hand, GNSS also relies on time: everything is based on the measurements of the signal travel time between the satellite and the receiver. GNSS therefore needs a reference timescale maintained by the operators and broadcast by the satellites. On the other hand, the satellite navigation systems offer a wonderful tool for time and frequency metrology, as these flying atomic clocks on board the satellites can be used as a reference for the comparison of ground time and frequency standards.

The tutorial will raise both aspects of the link between GNSS and TIME. After showing concretely the need for accurate time scales for the GNSS, the "GNSS time transfer" technique will be detailed. Code and carrier phase measurements will be presented and the procedure to get a precise and accurate clock comparison will be explained, both from the instrumental point of view and in terms of data analysis. GNSS Common View (or All in View) as well as Precise Point Positioning will be detailed in the presentation. The different error sources on the measurements will be studied and hence an ideal station setup will be presented.

Dr. Pascale Defraigne obtained her PhD in Geophysics in 1995 at the Université Catholique de Louvain. Since 1997 she manages the time and frequency activities at the Royal Observatory of Belgium, where the Belgian reference UTC (ORB) is maintained. Her research activities mainly concern the use of satellite navigation systems for time and frequency transfer. Dr. Defraigne presently chairs the CCTF working group on GNSS time transfer, and contributes to the validation of Galileo timing signals.

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Fiber Based Time and Frequency Transfer

Time: Monday, January 30, 2:30 p.m. - 3:30 p.m.
Room: Spyglass

The ability to utilize optical fibers for high performance time and frequency transfer has reached a high level of interest in recent years. The techniques are in discussion in a Bureau International des Poids et Mesures (BIPM) working group on Advanced Time and Frequency Transfer Techniques, and several research groups work actively on the topic, improving the performance. The fiber enables a connection between timing users that unlike GNSS signals, cannot easily be jammed or spoofed, and it has low enough uncertainties to compare the frequency of optical clocks.

Even though the techniques at a first glance may appear straightforward and simple, the fibers have imperfections and limitations. The best case is when a dedicated fiber is used, since the full flexibility of the fiber can be utilized, but there are still crucial parameters to take into account. Furthermore, when only a wavelength channel in an active communication network is available for time-transfer, an additional concern is that these networks are not designed for stable time transfer, which means that novel techniques must be implemented in the existing structure, for better accuracy and stability than common time transfer protocols such as NTP and PTP.

The tutorial will focus on the practical issues of optical telecommunication fibers, covering attenuation, scattering, propagation modes, dispersion, temperature dependence, amplification and detection, with the addition of typical network designs, and how these parameters influence the achievable quality of the time transfer. Finally, a review of the development of time transfer over fiber up to the present date will be given.

Dr. Sven-Christian Ebenhag received his PhD from Chalmers University of Technology in Sweden, with a thesis on frequency transfer techniques and applications in fiber optic communication systems. He has a past as hardware and software consultant for electronics. Since 2002 has he worked at the SP Technical Research Institute of Sweden, where he is one of the senior scientists in the implementations of time and frequency transfer over a national fiber communication network. He is also group leader for Time, Frequency, Photometry and Radiometry at SP Technical Research Institute of Sweden.

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Earth's Time Varying Rotation

Time: Monday, January 30, 3:45 p.m. - 4:45 p.m.
Room: Spyglass

The Earth's rotation is highly irregular. It varies on all observable time scales, from subdaily to decadal and longer. The gravitational attraction of the Sun, Moon, and planets causes the Earth to precess and nutate in space and, by periodically deforming the solid and fluid parts of the Earth, causes periodic changes in the Earth’s rate of rotation and wobble. Torques acting on the solid Earth associated with the transport of mass within the Earth’s atmosphere, hydrosphere, oceans, and core also change the Earth’s rotation as does mass displacement occurring within the solid Earth caused by earthquakes and other tectonic and non-tectonic motions like glacial isostatic adjustment. Measurements of the Earth’s rotation can therefore be used to gain greater understanding of a wide variety of geophysical and geodynamical processes. This tutorial will review the techniques used to measure variations in the Earth's rotation and the mechanisms that are causing it to vary.

Dr. Richard Gross received a Ph.D. degree in Geophysics from the University of Colorado at Boulder. Since 1988 he has worked at NASA's Jet Propulsion Laboratory were he is a Senior Research Scientist and Supervisor of the Geodynamics and Space Geodesy Group. His research interests include Earth rotation, time variable gravity and terrestrial reference frame determination. He is President of the International Astronomical Union's (IAU's) Commission A2 on Rotation of the Earth, Chair of the Science Panel of the International Association Geodesy's (IAG's) Global Geodetic Observing System, and Co-Chair of the IAU/IAG Joint Working Group on Theory of Earth Rotation and Validation.

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