All clock data, and time transfer data are For robustness, the low-noise system measuresĮach maser two ways, with different master clocks as references. Generate comparisons every 20 seconds, with a measurement noise of 2 picoseconds. Picoseconds (ps) RMS, which is less than the variation of a cesium clock overĪbout 5 picoseconds over an hour, we also measure them using a system to Three master clocks once per hour and store the data on multiple computers,Įach of which generates a timescale and is capable of controlling the masterĬlocks. Is based upon switches and counters that compare each clock against each of Outputs are sent to the measurement systems using cables that are phase-stableĪnd of low temperature coefficient and where possible all the connectors are On June 7, 2007, 70 standards were weighted The timescale is based only upon the Washington DC clocks. Within 0.1 degree C and whose relative humidities (for all masers and most Kept in 19 environmental chambers, whose temperatures are kept constant to The clocks used for the USNO timescale are Master Clock (AMC), located at Schriever Air Force Base in Colorado. Maser clocks, which are located in two Washington DC buildings and at the USNO Alternate Hewlett-Packard/Agilent/Symmetricom, 4 cesium CsIII-EP clocks made byĭatum/Symmetricom, and 24 cavity-tuned “Sigma-Tau/Datum/Symmetricom” hydrogen These, the largest group, almost half the staff, is directly involved in timeĭivided between those who service the clocks, those who monitor them, and thoseĬurrently have 69 HP5071 cesium clocks made by The most important part of the USNO Time Service Department is its staff, which This paper describes how time is generated at Systems, the USNO has specialized in real-time, robust timekeeping. Needs of GPS, as well were time and frequency requirements of other users and Well as coherent interferometry applications lead to future timing requirements Increasingly, cm-level positioning goals as Inference of the relevant clocks’ times to this level. Meter in 3 nanoseconds, was used for triangulation. Travel time, when converted to distance at the approximate rate of passing 1 Need for precise time was pushed to the nanosecond level because the light USNO were founded in part to measure the time for seafaring purposes. Many well-known observatories, such as Greenwich, the Observatory of Paris, and the IntroductionĪ crucial factor in navigation for centuries.

This paper describes some of the changes being made to meet the future needs for precision, accuracy, and robustness.

The USNO disseminates time via voice, telephone modem, LORAN, Network Time Protocol (NTP), GPS, and two-way satellite time transfer (TWSTT). The data used to generate UTC(USNO) are based upon 73 cesium and 21 hydrogen maser frequency standards in three buildings at two sites. Its Master Clock (MC) is the source of UTC(USNO), the USNO's realization of Coordinated Universal Time (UTC), which has stayed within 5 nanoseconds RMS of UTC since 1999.

The US Naval Observatory (USNO) has provided timing for the navy since 1830 and, in cooperation with other institutions, has also provided timing for the United States and the international community.

United states naval observatory