Long-term inconsistency between TWSTFT and GPS time transfer results in PTB-TL and NICT-TL time links

In this paper, we compared the TWSTFT and GPSPPP data for the PTB-TL, PTB-NICT, and NICT-TL time transfer links. We investigated the double difference between the time transfer data of TWSTFT and GPSPPP from 2005 to 2010. The results show two time transfer techniques had a conspicuously inconsistency and the patterns of double difference results were similar in PTB-TL and PTB-NICT links. The double difference results of all direct links exhibited the annual varying patterns, whose peak-to-peak phase difference in 1-day moving average are 4.5 ns both for the PTB-TL and PTB-NICT links, and 2 ns for NICT-TL link.