Time And Frequency Activities At Lne-Syrte Related To Global Navigation Satellite Systems

In modern navigation systems the distance measurements are based on the time spent by the information along the path between the emitter and the receiver. In all GNSS the user only receives signals broadcast from satellites, and the synchronization between all the clocks is crucial. The need of synchronization can be considered from two different point of view. In case of navigation the user must know in real time the time offset of each satellite with respect to a common time scale, like GPS system time or Galileo system time. In case of geodetic data analysis, made a-posteriori, the user will need a similar information but with a higher precision. One example are the data published by IGS that allow the estimation of the position at the millimeter level.