Recent Calibrations of UTC(NIST) - UTC(USNO)

摘要

The National Institute of Standards and Technology (NIST) and the United States Naval Observatory (USNO) use GPS common-view, carrier-phase time transfer and Two Way Satellite Time and Frequency Transfer (TWSTFT, also known as TWSTT) techniques in our time and frequency transfer applications and to compare our timescales. We have made five time transfer calibration measurements via TWSTFT since August 2010. In addition, one "hybrid" calibration was made via a cesium clock trip and TWSTFT, and another was made with a traveling GPS receiver. The TWSTFT calibrations agree with the TWSTFT differences within 1.6 ns peak to peak after the USNO TWSTFT station was rebuilt at the end of 2010. With the traveling GPS receiver, we used the carrier-phase Precise Point Positioning (PPP) technique to obtain the calibration result. If we use the TWSTFT calibration results to calibrate the operational PPP data, then the TWSTFT calibrations are also consistent with operational PPP to within 1.6 ns peak to peak. The calibration via PPP differs by 7 ns from that of the TWSTFT. The difference is most likely from the error in delay calibration of the PPP link. The hybrid calibration is consistent with the others, if its larger estimated uncertainties are taken into account. The possibility of reducing the uncertainties assigned by the BIPM is discussed.