GNSS time and frequency transfers through national positioning, navigation and timing infrastructure

Thayathip Thongtan; Sivinee Sawatdiaree; Chalermchon Satirapod

doi:10.1515/jag-2021-0061

Article

GNSS time and frequency transfers through national positioning, navigation and timing infrastructure

Thayathip Thongtan , Sivinee Sawatdiaree and Chalermchon Satirapod

Published/Copyright: December 24, 2021

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From the journal Journal of Applied Geodesy Volume 16 Issue 2

Abstract

GNSS signals have been a practical time transfer tool to realise a Coordinated Universal Time (UTC) and set civilian clocks around the world with respect to this atomic time standard. UTC time scale is maintained by the International Bureau of Weights and Measurements (BIPM) adjusted to be close to a time scale based on the Earth’s rotation. In Thailand, the official atomic time clocks are maintained by the National Institute of Metrology Thailand (NIMT) to produce UTC(NIMT) and Thailand standard time which is always 7 hours ahead of UTC(NIMT) because of the time zone differences between Greenwich and Bangkok. National Positioning, Navigation and Timing (PNT) infrastructure comprises of GNSS geodetic receivers uniformly distributed to continually observe GNSS signals, mainly for geodetic survey applications both real-time and post-processing services. NIMT is involved in order to provide time link to UTC and to determine the characteristics of GNSS receiver internal clocks; namely, fractional frequency offset and frequency stabilities by applying the GNSS time transfer techniques of common-view algorithms. Monitored time differences with respect to UTC(NIMT) are achieved from selected 4 ground stations in different parts of the country with observations of 21 days in order to determine the frequency stability at 1-day and 7-day modes. GNSS standard log files; in RINEX format, at these receivers are transformed into a time transfer standard format; CGGTTS, used to compute the time differences between two stations, the fractional frequency offset and the frequency stability. Averaged fractional frequency offsets are 2.8 × 10 − 13 Hertz/Hertz and computed Allan deviation is around 1.5 × 10 − 13 Hertz/Hertz for an averaging time of 1 day. The comparison of the national time scale and receiver clock offsets of every receivers in this national GNSS PNT infrastructure could be accomplished through common-view time transfer using GNSS satellites to maintain the time link of geodetic active control points to UTC as well as to determine receiver internal clock characteristics.

Keywords: GNSS time and frequency transfer; common-view

Acknowledgments

Most of this study results could not have been achieved without kind help of colleagues in the department of geodesy and geophysics, Royal Thai Survey Department (RTSD).

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Received: 2021-10-20

Accepted: 2021-12-07

Published Online: 2021-12-24

Published in Print: 2022-04-26

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https://doi.org/10.1515/jag-2021-0061

Keywords for this article

GNSS time and frequency transfer; common-view