GeoAzur Observatoire de la Cote dAzur

La Côte-Saint-André, France

GeoAzur Observatoire de la Cote dAzur

La Côte-Saint-André, France
SEARCH FILTERS
Time filter
Source Type

Samain E.,GeoAzur Observatoire de la Cote dAzur | Vrancken P.,German Aerospace Center | Guillemot P.,French National Center for Space Studies | Fridelance P.,Phusipus Inte;gration | Exertier P.,GeoAzur Observatoire de la Cote dAzur
Metrologia | Year: 2014

The T2L2 project (time transfer by laser link) allows for the synchronization of remote ultra-stable clocks over intercontinental distances (Fridelance et al 1997 Exp. Astron. 7, Samain and Fridelance 1998 Metrologia 35 151-9). The principle is derived from satellite laser ranging technology with dedicated space equipment designed to record arrival times of laser pulses at the satellite. The space segment has been launched in June 2008 as a passenger experiment on the ocean altimetry satellite Jason 2. T2L2 had been specified to yield a time stability of better than 1ps over 1000s integration time and an accuracy of better than 100ps. This level of performance requires a rigorous data processing which can be performed only with a comprehensive calibration model of the whole instrumentation. For this purpose, several experimental measurements have been performed before and during the integration phase of the T2L2 space instrument. This instrument model is one of the cornerstones of the data reduction process which is carried out to translate the raw information to a usable picosecond time transfer. After providing a global synopsis of the T2L2 space instrument, the paper gives a description of the experimental setup for the instrument characterization. It then details the different contributions within the calibration model and concludes with an applied example of a space to ground time transfer. © 2014 BIPM & IOP Publishing Ltd.


Guillemot P.,French National Center for Space Studies | Exertier P.,GeoAzur Observatoire de la Cote dAzur | Samain E.,GeoAzur Observatoire de la Cote dAzur | Pierron F.,GeoAzur Observatoire de la Cote dAzur | And 6 more authors.
42nd Annual Precise Time and Time Interval (PTTI) Systems and Applications Meeting 2010 | Year: 2010

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. © 2010 by Precise Time and Time Interval (PTTI) - Time Service Department.


Samain E.,GeoAzur Observatoire de la Cote dAzur | Exertier P.,GeoAzur Observatoire de la Cote dAzur | Courde C.,GeoAzur Observatoire de la Cote dAzur | Fridelance P.,Phusipus Integration | And 3 more authors.
Metrologia | Year: 2015

The Time Transfer by Laser Experiment (T2L2) on the Jason 2 satellite is a mission allowing remote clocks synchronization at the picosecond level. It is based on laser ranging technologies, with a laser station network on the ground and a dedicated instrument on board the satellite. It was launched in June 2008 and has been working continuously since then. T2L2 performances are very promising for time and frequency metrology and also for fundamental physics. The scientific objectives of the whole experiment rely on a rigorous uncertainty budget. This is governed by the characteristics of the space instrument and the laser stations network, the post treatment done on the ground, and also the process used to calibrate the laser stations. The uncertainty budget demonstrates that T2L2 is able to perform common-view time transfers between remote sites with an expanded uncertainty better than 140 ps (coverage factor = 2). © 2015 BIPM & IOP Publishing Ltd.


Bonnefond P.,Geoazur Observatoire de la Cote dAzur | Exertier P.,Geoazur Observatoire de la Cote dAzur | Laurain O.,Geoazur Observatoire de la Cote dAzur | Thibaut P.,Collecte Localisation Satellites | Mercier F.,French National Center for Space Studies
Advances in Space Research | Year: 2013

The Corsica site has been established in 1996 to perform altimeter calibration on TOPEX/Poseidon and then on its successors Jason-1 and Jason-2. The first chosen location was under the #85 ground track that overflight the Senetosa Cape. In 2005, it was decided to develop another location close to Ajaccio, to be able to perform the calibration of Envisat and in a next future of SARAL/AltiKa that will flight over the same ground tracks. Equipped with various instruments (tide gauges, permanent GPS, GPS buoy, weather station...) the Corsica calibration site is able to quantify the altimeter Sea Surface Height bias but also to give an input on the origin of this bias (range, corrections, orbits, ...). Due to the size of Corsica (not a tiny island), the altimeter measurement system (range and corrections) can be contaminated by land. The aim of this paper is to evaluate this land contamination by using GPS measurements from a fixed receiver on land and from another receiver onboard a life buoy. Concerning the altimeter land contamination, we have quantify that this effect can reach 8 mm/km and then affects the Sea Surface Height bias values already published in the framework of the Corsica calibration site by 5-8 mm for TOPEX and Jason missions. On the other hand, the radiometer measurements (wet troposphere correction) are also sensitive to land and we have been able to quantify the level of improvement of a dedicated coastal algorithm that reconciles our results with those coming from other calibration sites. Finally, we have also shown that the standard deviation of the GPS buoy sea level measurements is highly correlated (∼87%) with the Significant Wave Height derived from the altimeters and can be used to validate such parameter. © 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.


Guillemot P.,French National Center for Space Studies | Exertier P.,GeoAzur Observatoire de la Cote dAzur | Samain E.,GeoAzur Observatoire de la Cote dAzur | Pierron F.,GeoAzur Observatoire de la Cote dAzur | And 7 more authors.
43rd Annual Precise Time and Time Interval Systems and Applications Meeting 2011 | Year: 2011

The Time Transfer by Laser Link (T2L2) experiment, developed by both CNES and OCA, is aimed at performing ground to ground time transfer over intercontinental distances. The principle is derived from laser telemetry technology with dedicated space equipment designed to record arrival time of laser pulses at the satellite. Using laser pulses instead of radio frequency signals, T2L2 permits the realization of links between distant clocks with time stability of a few picoseconds and accuracy better than 100ps. The T2L2 space instrument on board the satellite Jason 2 has been in operation since June 2008. Several campaigns were done to estimate both the ultimate time accuracy and time stability capabilities. It includes mainly two kinds of experiments: the first involves two SLR stations on the same site and using the same clock, the second involves two remote SLR stations (Grasse and Paris) in common view. These experiments allowed the demonstration of both a time stability lower than a few tens of picoseconds for integration times from 10 s to 100 s and an accuracy lower than 100 ps for the T2L2 time transfer. Some important work has also been done to accurately compare T2L2 with microwave time transfer GPS and TWSTFT. These comparisons are based on laser station calibrations with a dedicated T2L2 event timer designed to accurately set the optical reference of the laser station within the PPS reference of the microwave systems. This paper presents ground to ground time transfer both in common view and non common view configuration, and comparisons between T2L2, GPS and Two-Way systems. Results of the 2010 campaigns are described as well as an insight into the future working plan.

Loading GeoAzur Observatoire de la Cote dAzur collaborators
Loading GeoAzur Observatoire de la Cote dAzur collaborators