Precise continuous time and frequency transfer using GPS carrier phase

The Astronomical Institute of the University of Bern (AIUB) and the Swiss Federal Office of Metrology and Accreditation (METAS) have been collaborating to investigate and apply the use of the GPS carrier phase measurements (GPS CP) for time and frequency transfer. At METAS a dedicated hardware has been developed: the so-called geodetic time transfer terminal (GeTT-terminal) which was already presented to the community [Dudle, 1998]. In parallel the AIUB has implemented the capability for time and frequency transfer into the Bernese GPS software package [Hugentobler, 2001]. Within the last years several improvements of the analysis software for the time and frequency transfer have been implemented. The developments have been focused on overcoming the day boundary discontinuities. These occur in the resulting time series if the data are analyzed independently for each day. The magnitude of these artificial "clock jumps" depends on the mean noise behavior of the code observations and may typically reach a magnitude of up to one nanosecond. An important result of the software developments is the possibility to reconnect the phase ambiguity parameters at the day boundaries which allows to generate a continuous geodetic time and frequency transfer solution for a time interval that is only limited by a loss of lock to all satellites. This allows, in addition, to generate a geodetic frequency transfer solution without using the code measurements at all. Consequences for the geodetic time transfer learned from applying the geodetic phase-only frequency transfer method in several international campaigns are discussed in this paper