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Session P1: Time Scales and Laboratory Activities

Using the RRS_Rapid Technique for Monitoring/Steering UTC(NIST)
Jian Yao, Judah Levine, and Thomas Parker, Time and Frequency Division, National Institute of Standards and Technology
Location: Regency B

UTC(NIST) is steered based on UTC and UTCr. To monitor the behavior of UTC(NIST) with a high precision and with a short latency, we have recently developed the GPS RRS_rapid technique, based on our earlier Revised RINEX-Shift (RRS) technique [1-2].
The RRS technique aims at eliminating the day-boundary-discontinuity problem in GPS carrier-phase time transfer. RRS runs PPP for a GPS-data batch of 10 days and extracts the PPP result at the middle epoch [1-2]. Considering the delay of IGS rapid products, the latency of RRS can be about 7 days in practice, which is a little too late to provide an up-to-date estimate of the behavior of UTC(NIST). RRS_rapid is the same as RRS, except that it extracts the PPP result at the beginning of the 10th day. Thus, the latency of RRS_rapid becomes about 3 days. Similar to RRS, there are no day-boundary discontinuities in the RRS_rapid result.
As a test, we “paper” steer AT1, the NIST free-running time scale, based on UTC data from BIPM Circular T and RRS_rapid. First, we frequency-steer AT1 to the average of UTC(PTB), UTC(USNO), and UTC(OP), using RRS_rapid. Since Cs/Rb fountains run almost continuously at PTB, USNO, and OP, frequency-steering AT1 to the average of these labs provides a very stable frequency reference. Second, UTC from BIPM Circular T is used for the time steering. The larger the time error is, the stronger the time steering becomes. The steering program runs automatically. The initial test shows that the steered AT1 is within +/- 5 ns with respect to UTC for 180 days, and its frequency stability is slightly worse than that of UTC(PTB/USNO/OP). We plan to run this automatic steering program over a longer period (e.g., 400 days) to provide a better evaluation of its performance. The latest result will be presented at the conference.
[1] Yao J, Levine J (2014) An improvement of RINEX-Shift algorithm for continuous GPS carrier-phase time transfer. In Proceedings of the 27th ION GNSS+ Conference, pp 1253-1260.
[2] Yao J, Skakun I, Jiang Z, Levine J (2015) A detailed comparison of two continuous GPS carrier-phase time transfer techniques. Metrologia 52(5):666-676.



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