Search

At NICT, Japan, research and developments for the time and frequency standards are performed by the Space-Time Standards Group. The objectives of this group are to establish standards and reference of space and time as the fundamental basis for various fields of activities in science, engineering, and social activities, and to provide easy access to these foundations from wide range of communities. The recent activities and achievements of the group are reported in this paper., Presented at the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (41st) held in Santa Ana Pueblo, NM on 16-19 November 2009. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting (41st), 221-230, 2009. The original document contains color images.

We have developed a new Two-Way Satellite Time and Frequency Transfer modem in order to improve measurement precision and reduce operational costs. The new modem is based on software-defined radio technology. Transmission and reception of signals between distinct ground stations are based on a pseudo-random noise code similar to the one used for GALILEO or GPS's modernized ranging signal. Our developed signal is introduced by a pair of pseudo-random noise codes that are separated in the frequency domain. The advantage of this signal is that the operational costs are below those of conventional signals, but yield better precision. We have recently carried out Two-Way Time Transfer experiment using the new signal. For evaluation of time transfer precision, GPS observations have been taken at the same time. Results show that the measurement precision of the new signal is better than 100 ps, and clock behavior of two stations was found to be consistent compared with GPS carrier-phase time transfer., See also ADM002186. Presented at the Precise Time and Time Interval Systems and Applications Meeting (40th Annual) held in Reston, VA on 1-4 December 2008. Published in the Proceedings of the Precise Time and Time Interval Systems and Applications Meeting (40th Annual), p459-466, 2008. The original document contains color images.

ETS-VIII, a Japanese geo-stationary satellite, launched in December 2006, has been developed to obtain the fundamental technologies for satellite positioning systems using two onboard cesium atomic clocks. At NICT, we developed Time Comparison Equipment (TCE) both onboard ETS-VIII and in the Earth station for precise time transfer between the atomic clocks on the satellite and a ground reference clock. Using code and carrier-phase data measured by TCE, the time and frequency difference between the onboard atomic clock and that on the ground is calculated by the Two-Way Satellite Ground Time and Frequency Transfer (TWSGTFT) method. Since February 2007, we have carried out the experiment to confirm the performance of TCE in orbit after the launch. As a result, we confirmed that TCE is able to measure the code phase with subnanosecond precision and measure the carrier phase with a few-picosecond precision., Presented at the Annual Precise Time and Time Interval (PTTI) Meeting (39th) held in Long Beach, CA on 26-29 Nov 2007. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Meeting (39th), p449-458, 2007. The original document contains color images.

Instead of a hydrogen maser, a carefully selected Crystal oscillator which is phase locked to a Cesium (Cs) frequency standard for time range of more than 100 seconds is adopted to the time and frequency standard of a geodetic VLBI experiment. The domestic VLBI experiment with 55km baseline using the Crystal oscillator at one end was made in Japan and the obtained error of the baseline vector components were 4cm, and that of the baseline length was 3cm. This system may be operated after only 2 hours warm up. These results coincides with those of conventional geodetic Laser ranging and VLBI using a hydrogen maser within the formal error. A VLBI experiment with over 1000km baselines were carried out successfully from October 1988, and over 11000km baseline bctween Japan and Antarctica was carried out succcssfully in January 1990., See also ADA239372. Presented at the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd) held in Vienna, VA on 4-6 December 1990. Published in the Proceedings of the Annual Precise Time and Time Interval (PTTI) Applications and Planning Meeting (22nd), p131-143, December 1990.