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Showing results 41 to 60 of 172
   Reply to Comment on: ‘The quest for a consistent signal in ground and GRACE gravity time series’; ; et al in Geophysical Journal International (2014), 199(3), 1818-1822 Detailed reference viewed: 248 (4 UL)Future and development of the European Combined Geodetic Network ECGN; ; et al in Rizos, C.; Willis, Pascal (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014) Detailed reference viewed: 147 (1 UL) The quest for a consistent signal in ground and GRACE gravity time series; ; et al in Geophysical Journal International (2014), 197 Detailed reference viewed: 161 (15 UL)Accurate Determination of the Earth Tidal Parameters at the BIPM to Support the Watt Balance ProjectFrancis, Olivier  ; Rothleitner, Christian ; in Rizos, C.; Willis, P. (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014) Detailed reference viewed: 157 (14 UL)Tidal gravity measurements in Southeast Asia revisitedFrancis, Olivier ; van Dam, Tonie in Sun, Heping (Ed.) Progress on Geodesy and Geodynamics (2014) Detailed reference viewed: 194 (25 UL)Détermination de l'accélération de la pesanteur pour la balance du watt du LNE; ; et al in Revue Française de Métrologie (2014), 36(2014-4), 11-27 The “watt balance” project aims at linking the kilogram definition to the Planck constant. The weighing of the mass involved requires a determination of the acceleration g with an uncertainty better than ... [more ▼] The “watt balance” project aims at linking the kilogram definition to the Planck constant. The weighing of the mass involved requires a determination of the acceleration g with an uncertainty better than 10-8. This work aims at determining g with an atomic gravimeter and a dedicated gravimetric site. [less ▲] Detailed reference viewed: 194 (2 UL)Absolute gravity measurements at the Conrad Observatory by the University of LuxembourgFrancis, Olivier Article for general public (2014) Detailed reference viewed: 152 (12 UL)Measurement of the speed-of-light perturbation of free-fall absolute gravimetersRothleitner, Christian ; ; Francis, Olivier in Metrologia (2014), 51(3), 9 We report on a direct measurement of the relativistic Doppler shift with a commercial free-fall absolute gravimeter of the type FG5X. The observed Doppler shift, which is commonly called speed-of-light ... [more ▼] We report on a direct measurement of the relativistic Doppler shift with a commercial free-fall absolute gravimeter of the type FG5X. The observed Doppler shift, which is commonly called speed-of-light perturbation, can be well described by the relativistic Doppler formula, where the constant object velocity is replaced by a time-dependent velocity with constant acceleration. The observed speed-of-light perturbation stands in contrast to other publications, which predict a higher frequency shift. It has been measured with a relative uncertainty of 1.1 × 10 −3 . [less ▲] Detailed reference viewed: 88 (6 UL)Measuring the Newtonian Constant of Gravitation with a differential free-fall gradiometer - a feasibility studyRothleitner, Christian ; Francis, Olivier in Review of Scientific Instruments (2014), 85 Detailed reference viewed: 149 (12 UL)The Decade of the Geopotential - techniques to observe the gravity field from spaceWeigelt, Matthias ; van Dam, Tonie ; Francis, Olivier Scientific Conference (2013, October) Detailed reference viewed: 81 (3 UL)ECAG-2011: European Compariosn of Absolute Gravimeters 2011, Walferdange, LuxembourgFrancis, Olivier Report (2013) Detailed reference viewed: 82 (10 UL)Constraints on the upper crustal magma reservoir beneath Yellowstone Caldera inferred from lake-seiche induced strain observations; ; Francis, Olivier et alin Geophysical Research Letters (2013), 40(3), 501--506 Detailed reference viewed: 126 (14 UL)Comparison of recent ocean tide models with gravimetric and GPS observationsvan Dam, Tonie ; Weigelt, Matthias ; Francis, Olivier et alScientific Conference (2013) Detailed reference viewed: 188 (21 UL)The European Comparison of Absolute Gravimeters 2011 (ECAG-2011) in Walferdange, Luxembourg: results and recommendationsFrancis, Olivier ; ; et alin Metrologia (2013), 50(3), 257 We present the results of the third European Comparison of Absolute Gravimeters held in Walferdange, Grand Duchy of Luxembourg, in November 2011. Twenty-two gravimeters from both metrological and non ... [more ▼] We present the results of the third European Comparison of Absolute Gravimeters held in Walferdange, Grand Duchy of Luxembourg, in November 2011. Twenty-two gravimeters from both metrological and non-metrological institutes are compared. For the first time, corrections for the laser beam diffraction and the self-attraction of the gravimeters are implemented. The gravity observations are also corrected for geophysical gravity changes that occurred during the comparison using the observations of a superconducting gravimeter. We show that these corrections improve the degree of equivalence between the gravimeters. We present the results for two different combinations of data. In the first one, we use only the observations from the metrological institutes. In the second solution, we include all the data from both metrological and non-metrological institutes. Those solutions are then compared with the official result of the comparison published previously and based on the observations of the metrological institutes and the gravity differences at the different sites as measured by non-metrological institutes. Overall, the absolute gravity meters agree with one another with a standard deviation of3.1 µ Gal. Finally, the results of this comparison are linked to previous ones. We conclude with some important recommendations for future comparisons. [less ▲] Detailed reference viewed: 210 (18 UL)On the gravimetric contribution to watt balance experiments; ; Francis, Olivier et alin Metrologia (2013), 50(5), 452 It has been recommended that the relative standard uncertainty of the numerical value of the Planck constant required for the redefinition of the kilogram should not exceed 2 × 10 −8 . To reach this goal ... [more ▼] It has been recommended that the relative standard uncertainty of the numerical value of the Planck constant required for the redefinition of the kilogram should not exceed 2 × 10 −8 . To reach this goal using experiments based on a watt balance, the free-fall acceleration ( g ) traceable to the SI, at a given point and a given time, needs to be known with a sufficiently small uncertainty well below 2 × 10 −8 . Reducing the uncertainty in g allows the other uncertainties related to the watt balance to be increased. Instead of a simultaneous operation of an absolute gravimeter with a watt balance, we propose an alternative approach and demonstrate that a standard uncertainty below 5 µGal (relative uncertainty of 5 × 10 −9 ) is reachable under the conditions at BIPM. Further decreasing the uncertainty could significantly increase commitments in terms of personnel and equipment and would not significantly improve the uncertainty targeted for the BIPM watt balance experiment. A 5 µGal uncertainty might also satisfy the needs of other watt balance experiments underway or planned. In our approach we combine the following information: (1) the Key Comparison Reference Values obtained from the CCM.G-K1, a key comparison carried out in the frame of the International Comparison of Absolute Gravimeters in 2009 (ICAG2009); (2) the accurate gravity network established using the qualified absolute and relative gravimeters; (3) temporal gravity variations based on observed Earth-tide parameters and modelled effects of polar motion and atmospheric mass redistribution; (4) uncertainty estimates that account for non-modelled effects; (5) the option to carry out absolute gravity measurements once every one or two years with two or more gravimeters for monitoring the stability of the gravity field at the BIPM. [less ▲] Detailed reference viewed: 129 (1 UL)Absolute Gravity Measurements at the Conrad Observatorium in Austria in June 2012Francis, Olivier Report (2012) Detailed reference viewed: 54 (4 UL)Absolute Gravity Measurements ath the Geodynamics Observatory in Moxa (Germany)Francis, Olivier Report (2012) Detailed reference viewed: 51 (2 UL)Updating the Precise Gravity Network at the BIPM; ; et al in Geodesy for Planet Earth (2012) Detailed reference viewed: 175 (12 UL)ECAG-2011 期间 FG5/232 绝对重力仪观测及结果分析; ; et al in 大地测量与地球动力学 (2012), 32(4), Detailed reference viewed: 3461 (17 UL)Results of the first North American comparison of absolute gravimeters, NACAG-2010; Francis, Olivier ; et alin Journal of Geodesy (2012), 86 Detailed reference viewed: 115 (2 UL) |
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