Use of the Global Navigation Satellite Systems for the Construction of the International Time Reference UTC

Abstract

The International Bureau of Weights and Measures (BIPM) has the mandate to generate and distribute the international time scales Coordinated Universal Time (UTC) and International Atomic Time (TAI). About 400 atomic clocks belonging to national timing laboratories world-wide are used to generate UTC/TAI at the BIPM. Clock comparison is the key issue in the generation of any international time scale based on individual clock readings. Considering that in the case of UTC the clocks are located in remote laboratories, the use of time and frequency transfer techniques is necessary. Time transfer by Global Navigation Satellite System (GNSS), at present consisting mainly of the American GPS and the Russian GLONASS, constitutes the major technique used in the computation of UTC/TAI. To enable higher accuracy and robustness, a multi-system strategy is indispensable. Combined GPS and GLONASS time transfer has already been implemented at the BIPM with excellent results. In the near future it will be desirable to incorporate the Chinese BeiDou and the European Galileo systems in the computation of UTC/TAI. The GNSS time and frequency transfer is completed with another spatial technique, the Two-Way Satellite Time and Frequency Transfer (TWSTFT), that is completely independent of GNSS. In this paper, we present the applications of GNSS to accurate time and frequency transfer; we describe new data processing techniques such All in View (AV), Precise Point Positioning (PPP) and combined multi-system solutions; we analyze the corresponding uncertainties and introduce the BIPM’s new projects.