Transatlantic time and frequency transfer by GPS carrier phase

Over the last years there has been a growing interest in GPS carrier phase as a tool for time and frequency transfer. This technique, also known as Geodetic Time Transfer (GeTT), has been studied intensively in the frame of a collaboration between the Swiss Federal Office of Metrology (OFMET) and the Astronomical Institute of the University of Bern (AIUB). The results obtained over European baselines and presented at previous EFTF meetings have demonstrated the suitability of GeTT as method of frequency comparison between high performance clocks since much shorter averaging times would be required than with GPS Common View. In this study the focus is on a campaign between the Physikalisch Technische Bundesanstalt in Germany (PTB) and the US Naval Observatory, Washington (USNO). Besides the longer baseline the. Choice of these two sites offers also the possibility to compare frequently GeTT and TWSTFT. First results indicate that sub-nanosecond time transfer is possible by this new technique. The PTB-USNO campaign is the longest GeTT campaign carried out to this elate. The long term behaviour of the terminals will, therefore, also be addressed.