Changes in the long-term stability of GPS, GLONASS and Galileo clocks based on the IGS repro3 campaign

Abstract Time is the basis of satellite navigation systems. In precision studies, it is additionally important to ensure accuracy at the highest possible level, up to sub-millimetres. For this purpose, corrections of the clocks of satellites and GNSS reference stations are made available. This type of data is made available in real time in a navigation dispatch with an interval of 10 min–2 h depending on the GNSS system, or in a precision orbit file (interval of 15 min) or in the form of clock correction files (30 s or 300 s). This paper analyses the long-term stability of the clocks of satellites of four GNSS systems. For this purpose, IGS reprocessing data from 1994 to 2020 were used and ADEV (Allan deviation) and three related variances were adopted. The study showed the different nature of the satellite correction for each GNSS system and the increase of the stability over time.