TIME TRANSFER BETWEEN USNO AND PTB: OPERATION AND CALIBRATION RESULTS

摘要

Two-way satellite time and frequency transfer (TWSTFT) is routinely executed between USNO and PTB via two links, using a connection at Ku-band and X-band. The Ku-band measurements are performed five times per week (in collaboration with several European and American time laboratories). The X-band link is unique: measurements are carried out nominally 24 times per day. By this means, hydrogen masers of both laboratories are compared during 15 minutes each hour. Since June 2003, the X-band results have been evaluated by the BIPM for future use in the production of TAI. Thus, a periodic calibration of the link is strongly desirable. Up to now, three calibration experiments were carried out with a transportable TWSTFT station provided by USNO: in June 2002, January 2003, and July 2003. Because only a few TWSTFT calibrations of civil time laboratories were performed up to now, this first "semiannual" schedule provides a good opportunity to characterize the stability of TWSTFT links. For example, the January 2003 exercise confirmed that the internal delays of the Ku-band as well as of the X-band link were stable within 1 nanosecond. During autumn 2003, the satellite used in the Ku-band link had to be exchanged, which caused a gap in the data of about 3 weeks. Using other time transfer techniques, the gap was bridged with an uncertainty of 1 ns.