Time Transfer by Laser Link T2L2: First Results of the 2010 Campaign

Abstract : The Time Transfer by Laser Link (T2L2) experiment has to perform ground-to-ground time transfer using time tagged laser pulses propagating back and forth between the ground and the Jason-2 satellite. The expected time stability is 1 ps over 1000 s and 10 ps over 1 day and a time accuracy in the 100 ps range. The T2L2 experiment is a joint CNES and OCA space mission. A payload has been installed inside the Jason-2 satellite, which was launched in June 2008. This payload includes some corner cubes (LRA, provided by the JPL), the T2L2 instrument itself, and an ultra-stable quartz oscillator to date the events. The ground network relies on existing laser stations (ILRS network), among them the two stations of the OCA: a fixed one at Grasse and a transportable one currently installed at Observatoire de Paris. Both stations include laser pulses emitter and receptor synchronized on a clock. First ground-to-space time transfers have demonstrated noise levels of some tens of picoseconds 0 and a preliminary time stability of a few picoseconds over integration times of some tens of seconds, clearly limited by the on-board clock [4]. The current campaign began in June 2010 and involved eight laser stations in Europe and Asia. As some laser stations are also equipped by GPS and TWSTFT devices, this campaign should allow the performance comparisons between these systems operating with different wavelengths and, consequently, different atmosphere delays. With the installation of the SYRTE Mobile Atomic Fountain at OCA (Grasse) and the transportable laser station at SYRTE (Paris), we will perform a time and frequency transfer by laser link between the cold atomic fountains 0 with a frequency accuracy in the 10-16 range. The paper will present the first results of the ground-to-ground time transfer, in common clock and non-common-clock configuration, and a first comparison with GPS.