European two-way satellite time transfer experiments using the INTELSAT (VA-F13) satellite at 307°E

A two-way satellite time and frequency transfer (TWSTFT) experiment performed between six European laboratories is reported. Transfers were made on a regular basis over a period of six months. TWSTFT was demonstrated to be a useful method to compare a relatively large number of atomic clocks internationally, as an alternative to the method of common view of global positioning system (GPS) satellites. The GPS common view time transfer method and TWSTFT method were compared over the same link for a period of 150 days. Three TWSTFT´s have been performed simultaneously. Time transfers were performed over periods of up to 8 h, enabling the measurement noise of the TWSTFT system and the stability of the atomic clocks to be examined. Time transfers were made in consecutive successions between clocks at three distant Earth stations. Closing errors of up to approximately 4 ns were observed. The magnitude of these closing errors justified further examination. The uncertainties in the determination of the closing errors have been examined along with their origin, characteristics, and dependence on operating parameters