Defraigne, Pascale

Seminar presented at Tutorial of the EFTF on 2018-04-09

Abstract: Global Navigation Satellite Systems (GNSS) has been growing in the last years. After long standing GPS and GLONASS constellations, some new global and regional systems are now providing positioning and timing systems: Galileo, BeiDou, QZSS, INRSS, and other augmentation systems. GNSS and Time have a bi-directional relationship. On the one hand, GNSS relies on time: everything is based on the measurements of the signal travel time between the satellite and the receiver. GNSS therefore needs a reference timescale maintained by the operators and broadcast by the satellites. On the other hand, the satellite navigation systems offer a wonderful tool for time and frequency metrology, as these flying atomic clocks onboard the satellites can be used as a reference for the comparison of ground time and frequency standards. This tutorial will raise both aspects of the link between GNSS and TIME. After a presentation of the different constellations and principles of the GNSS, the needs of these systems for accurate time scales will be explained. In a second part of the tutorial, the 'GNSS time transfer' technique will be detailed. Code and carrier phase measurements will be presented and the procedure to get a precise and accurate clock comparison will be explained, both from the instrumental point of view and in terms of data analysis. GNSS Common View (or All in View) as well as Precise Point Positioning will be detailed in the presentation. The different error sources on the measurements will be studied and hence an ideal station set-up for timing applications will be presented.