BIPM calibration scheme for UTC time links — BIPM pilot expermiment to strenghen Asia-Europe very long baselines

The calibration uncertainty (u_B) is the dominant part in the total uncertainty budget of the UTC generation. There are two calibration strategies: (a) Receiver calibration and (b) Time link calibration. The state-of-the-art of the u_B is of order 5 ns for GNSS time transfer based on the strategy (a) and is 1 ns for TWSTFT based on the strategy (b) in which the absolute offset is canceled. In the BIPM Circular T, the uncertainty in UTC-UTC(k) is obtained from the uncertainties in the links. To reduce the uncertainty in UTC-UTC(k), it is optimal to use the calibration strategy (b). Earlier investigations gave theoretical and practical proofs. Based on these studies, we propose the BIPM calibration scheme using a calibration system composed of three GNSS geodesic receivers: one is stationary at BIPM and the other two travel between the laboratories. We describe the set-up of the system, the schedule, the uncertainty u_B and aging of the u_B. The u_B is expected to be better than 2 ns for even very long inter-continental UTC baselines.