We report on a new test of the gravitational redshift and thus of local position invariance, an integral part of the Einstein equivalence principle, which is the foundation of general relativity and ...all metric theories of gravitation. We use data spanning 1008 days from two satellites of Galileo, Europe's global satellite navigation system, which were launched in 2014, but accidentally delivered on elliptic rather than circular orbits. The resulting modulation of the gravitational redshift of the onboard atomic clocks allows the redshift determination with high accuracy. Additionally, specific laser ranging campaigns to the two satellites have enabled a good estimation of systematic effects related to orbit uncertainties. Together with a careful conservative modeling and control of other systematic effects we measure the fractional deviation of the gravitational redshift from the prediction by general relativity to be (0.19±2.48)×10^{-5} at 1 sigma, improving the best previous test by a factor 5.6. To our knowledge, this represents the first reported improvement on one of the longest standing results in experimental gravitation, the Gravity Probe A hydrogen maser rocket experiment back in 1976.
For many years, lunar laser ranging (LLR) observations using a green wavelength have suffered an inhomogeneity problem both temporally and spatially. This paper reports on the implementation of a new ...infrared detection at the Grasse LLR station and describes how infrared telemetry improves this situation. Our first results show that infrared detection permits us to densify the observations and allows measurements during the new and the full Moon periods. The link budget improvement leads to homogeneous telemetric measurements on each lunar retro-reflector. Finally, a surprising result is obtained on the Lunokhod 2 array which attains the same efficiency as Lunokhod 1 with an infrared laser link, although those two targets exhibit a differential efficiency of six with a green laser link.
The Time Transfer by Laser Link (T2L2) is a very high resolution time transfer technique based on the recording of arrival times of laser pulses at the satellite. T2L2 was designed to achieve time ...stability in the range of 1ps over 1000s and an accuracy better than 100ps. The project is in operation onboard the Jason-2 satellite since June 2008. The principle is based on the Satellite Laser Ranging (SLR) technology; it uses the input of 20–25 SLR stations of the international laser network which participate in the tracking. This paper focuses on the data reduction process which was developed specifically to transform the raw information given by both space instrument and ground network: first to identify the triplets (ground and onboard epochs and time of flight of the laser pulse), second to estimate a usable product in terms of ground-to-space time transfer (including instrumental corrections), and thirdly to produce synchronization between any pair of remote ground clocks. In describing the validation of time synchronizations, the paper opens a way for monitoring the time difference between ultra-stable clocks thanks to a laser link at a few ps level for Common View passes. It highlights however that without accurately characterizing the onboard oscillator of Jason-2 and knowing the unavailability of time calibrations of SLR stations generally, time transfer over intercontinental distances remain difficult to be accurately estimated.
The Time Transfer by Laser Link (T2L2) experiment on-board the Jason-2 satellite was launched in June 2008 at 1335km altitude. It has been designed to use the Satellite Laser Ranging (SLR) space ...technique as an optical link between ground and space clocks. T2L2, as all the instruments aboard Jason-2, is referenced to the Ultra Stable Oscillator (USO) provided by the Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) system. A complex data processing has been developed in order to extract time & frequency products as the relative frequency bias of the USO from ground-to-space time transfer passages. The precision of these products was estimated of a few parts in 10−13 given the very good in-flight performance of T2L2 with a ground-to-space time stability of a few picoseconds (ps) over 100s. Frequency bias from T2L2 were compared with results from operational orbit computation, notably with the DIODE (Détermination Immédiate d’Orbite par Doris Embarqué) outputs (see Jayles et al. (2016) same issue) at the level of 1·10−12.
The present paper is focusing on the main physical effects which drive the frequency variations of the Jason-2 USO during its flight, notably over the South Atlantic Anomaly (SAA) area. In addition to the effects of radiation we studied the effect of the residual temperature variations, in the range 8–11°C (measured on-board). A model was established to represent these effects on the short term with empirical coefficients (sensitivities of the USO) to be adjusted. The results of fitting the model over ∼200 10-day periods, from 2008 to 2014, show the sensitivities of the Jason-2 USO to temperature and radiation. The analysis of the 6-year output series of empirical coefficients allows us to conclude that: (i) the temperature to frequency dependence is very stable along time at the level of around −1.2·10−12per°C, (ii) the radiation effects are much lower than those previously detected on the Jason-1 USO with a factor>10. The swept material used by manufacturers for the Jason-2 quartz oscillator has such properties to avoid non-linear effects >1–2·10−12, (iii) the model is available at 1min or less over the Jason-2 mission, with a level of consistency of 5·10−13, which is the average RMS of the post-fit residuals.
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).
In this work, we report recent progress on the design of all-fibered ultra-high repetition-rate pulse sources for telecommunication applications around 1550
nm. The sources are based on the ...non-linear compression of an initial beat-signal through a multiple four-wave mixing process taking place into an optical fiber. We experimentally demonstrate real-time monitoring of a 20
GHz pulse source having an integrated phase noise 0.01 radian by phase locking the initial beat note against a reference RF oscillator. Based on this technique, we also experimentally demonstrate a well-separated high-quality 110
fs pulse source having a repetition rate of 2
THz. Finally, we show that with only 1.4
m of standard single mode fiber, we can achieve a twofold increase of the repetition rate, up to 3.4
THz, through the self-imaging Talbot effect. Experimental results are supported by numerical simulations based on the generalized non-linear Schrödinger equation.
We present a direct comparison between two satellite time transfer techniques on independently calibrated links: Time Transfer by Laser Link (T2L2) and Common-Views (CV) of satellites from the Global ...Positioning System (GPS) constellation. The GPS CV and T2L2 links between three European laboratories where independently calibrated against the same reference point of the local timescales. For all the links the mean values of the differences between GPS CV and T2L2 are equal or below 240 ps, with standard deviations below 500 ps, mostly due to GPS CV. Almost all deviations from 0 ns are within the combined uncertainty estimates. Despite the weak number of common points obtained, due to the fact that T2L2 is weather dependent, these results are providing an unprecedented sub-ns consistency between two independently calibrated microwave and optical satellite time transfer techniques.
Tahiti is a unique geodetic site located in the south Pacific Ocean where few observatories exist nearby. The American mobile station MOBLAS-8 was installed in Tahiti in 1998, and GPS and DORIS ...systems were also deployed in its vicinity in order to develop this site into one of the fundamental colocated sites of the International Terrestrial Reference Frame. In order to make a new estimate of the colocation differences between the different techniques, a campaign of the French Transportable Laser Ranging System (FTLRS) was conducted in Tahiti between April and October 2011. The FTLRS was deployed close to the existing equipment. Observations for LAGEOS 1, LAGEOS 2 and Starlette were studied, and the solutions to the local ties between FTLRS, MOBLAS-8, DORIS and GPS were evaluated. Our results of the geodetic local-ties between laser stations and GPS agree well with the measurements made by the Institut National de l’Information Géographique et Forestière (IGN) during the campaign, with differences less than 2 mm in the vertical direction. The laser station range biases as a function of satellites are also presented,
-
3
(
±
2) mm for MOBLAS-8 and 3 (
±
3) mm for FTLRS, respectively. In addition, we investigated the role of time bias (ranging from a few hundreds of nanoseconds to one microsecond) given by the Time Transfer by Laser Link experiment, which shows a limited impact on the present SLR analysis. We also compared the coordinates of the three available techniques at Tahiti, i.e., laser, GPS and DORIS. We found the accuracy of laser solutions still needs to be improved, so that the SLR at Tahiti could contribute more effectively to the tracking of satellites and thus to the international reference frame. This study is useful in evaluating the SLR and other space techniques in order to prepare the deployment of new equipment in Tahiti in the near future.
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