![]() ; ; et al Scientific Conference (2016) Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole ... [more ▼] Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole. Among these techniques, gravimetry has been increasingly used in the last decade to characterize the hydrological behavior of complex systems, e.g. karst environments or volcanoes. We present a continuous microgravimetric monitoring of 3 years in the karstic area of Rochefort (Belgium), that shows multiple occurrences of caves and karstic features. The gravity record includes measurements of a GWR superconducting gravimeter, a Micro-g LaCoste gPhone and an absolute FG5 gravimeter. Together with meteorological measurements and a surface/in-cave hydrogeological monitoring, we were able to improve the knowledge of hydrological processes. On the one hand, the data allowed identifying seasonal groundwater content changes in the unsaturated zone of the karst area, most likely to be linked to temporary groundwater storage occurring in the most karstified layers closed to the surface. Combined with additional geological information, modelling of the gravity signal based on the vertical potential of the gravitational attraction was then particularly useful to estimate the seasonal recharge leading to the temporary subsurface groundwater storage. On the other hand, the gravity monitoring of flash floods occurring in deeper layers after intense rainfall events informed on the effective porosity gradient of the limestones. Modelling was then helpful to identify the hydrogeological role played by the cave galleries with respect to the hosting limestones during flash floods. These results are also compared with measurements of an in-cave gravimetric monitoring performed with a gPhone spring gravimeter. An Electrical Resistivity Tomography monitoring is also conducted at site and brings additional information useful to verify the interpretation made with the gravimetric monitoring [less ▲] Detailed reference viewed: 61 (2 UL)![]() ; ; Francis, Olivier ![]() Poster (2015, September 06) Detailed reference viewed: 192 (12 UL)![]() Francis, Olivier ![]() Report (2015) Detailed reference viewed: 125 (11 UL)![]() Francis, Olivier ![]() Report (2015) Detailed reference viewed: 114 (16 UL)![]() Francis, Olivier ![]() Report (2015) Detailed reference viewed: 174 (24 UL)![]() Francis, Olivier ![]() in Marées Terrestres Bulletin d'Informations (2015), 149 Detailed reference viewed: 185 (18 UL)![]() Francis, Olivier ![]() in Metrologia (2015), 52(1A), 07009 In November 2013 an International Key Comparison, CCM.G-K2, was organized in the Underground Laboratory for Geodynamics in Walferdange. The comparison has assembled 25 participants coming from 19 ... [more ▼] In November 2013 an International Key Comparison, CCM.G-K2, was organized in the Underground Laboratory for Geodynamics in Walferdange. The comparison has assembled 25 participants coming from 19 countries and four different continents. The comparison was divided into two parts: the key comparison that included 10 NMIs or DIs, and the pilot study including all participants. The global result given by the pilot study confirms that all instruments are absolutely coherent to each other. The results obtained for the key comparison confirm a good agreement between the NMI instruments. Main text. To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/M/G-K2/CCM.G-K2.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA). [less ▲] Detailed reference viewed: 489 (44 UL)![]() ; ; et al Poster (2014, September 14) Detailed reference viewed: 134 (5 UL)![]() ; ; et al in Rizos, C.; Willis, Pascal (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014) Detailed reference viewed: 159 (1 UL)![]() ; ; et al in Geophysical Journal International (2014), 197 Detailed reference viewed: 168 (16 UL)![]() Rothleitner, Christian ![]() ![]() 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: 93 (7 UL)![]() Rothleitner, Christian ![]() ![]() in Review of Scientific Instruments (2014), 85 Detailed reference viewed: 160 (12 UL)![]() ; ; 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: 208 (2 UL)![]() ; ; Francis, Olivier ![]() in Journal of Geodesy (2014), 88(6), 617-622 Detailed reference viewed: 275 (8 UL)![]() ; ; Francis, Olivier ![]() in Rizos, C.; Willis, P. (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014) Detailed reference viewed: 145 (9 UL)![]() Francis, Olivier ![]() ![]() in Rizos, C.; Willis, P. (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014) Detailed reference viewed: 167 (14 UL)![]() Francis, Olivier ![]() ![]() in Sun, Heping (Ed.) Progress on Geodesy and Geodynamics (2014) Detailed reference viewed: 201 (25 UL)![]() Francis, Olivier ![]() Article for general public (2014) Detailed reference viewed: 162 (12 UL)![]() ; ; et al in Geophysical Journal International (2014), 199(3), 1818-1822 Detailed reference viewed: 258 (4 UL)![]() ; Francis, Olivier ![]() in Metrologia (2014), 51(5), 15-17 We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter (CAG) and FG5X#216 of the Université du Luxembourg ... [more ▼] We report the direct comparison between the stabilities of two mobile absolute gravimeters of different technology: the LNE-SYRTE Cold Atom Gravimeter (CAG) and FG5X#216 of the Université du Luxembourg. These instruments rely on two different principles of operation: atomic and optical interferometry. The comparison took place in the Walferdange Underground Laboratory for Geodynamics in Luxembourg, at the beginning of the last International Comparison of Absolute Gravimeters, ICAG-2013. We analyse a 2h10 duration common measurement, and find that the CAG shows better immunity with respect to changes in the level of vibration noise, as well as a slightly better short term stability. [less ▲] Detailed reference viewed: 126 (7 UL) |
||