Regional comparison of absolute gravimeters SIM.M.G-K1 key comparison

in Metrologia (2017), 54(1A), 07019

Twelve absolute gravimeters were compared during the regional Key Comparison SIM.M.G-K1 of absolute gravimeters. The four gravimeters were from different NMIs and DIs. The comparison was linked to the CCM ... [more ▼]

Twelve absolute gravimeters were compared during the regional Key Comparison SIM.M.G-K1 of absolute gravimeters. The four gravimeters were from different NMIs and DIs. The comparison was linked to the CCM.G-K2 through EURAMET.M.G-K2 via the DI gravimeter FG5X-216. Overall, the results and uncertainties indicate an excellent agreement among the gravimeters, with a standard deviation of the gravimeters' DoEs better than 1.3 μGal. In the case of the official solution, all the gravimeters are in equivalence well within the declared uncertainties. == 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-K1/SIM.M.G-K1.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 the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA). [less ▲]

Study of space weather impact on Antarctica ionosphere from GNNS data

Poster (2016, April 29)

The impact of solar activity on the ionosphere at polar latitudes is not well known compare to low and mid-latitudes due to lack of experimental observations, especially over Antarctica. Consequently, one ... [more ▼]

The impact of solar activity on the ionosphere at polar latitudes is not well known compare to low and mid-latitudes due to lack of experimental observations, especially over Antarctica. Consequently, one of the present challenges of the Space Weather community is to better characterize (1) the climatological behavior of the polar ionosphere in response to variations of the solar activity and (2) the different response of the ionosphere at high latitudes during extreme solar events and geomagnetic storms. For that, the combination of GNSS measurements (e.g. GPS, GLONASS and Galileo) on two separate frequencies allows determining the ionospheric delay between a ground receiver and a satellite. This delay is function of the integrated number of electrons encountered in the ionosphere along the signal ray path, called the Total Electron Content (TEC). It is thus possible to study the behavior of ionospheric TEC at different time and spatial scales from the observations of a network of permanent GNSS stations. In the frame of GIANT-LISSA and IceCon projects we installed since 2009 five GNSS stations around the Princess Elisabeth station. We used these stations additionally to other stations from the IGS global network to estimate the ionospheric TEC at different locations over Antarctica. This study presents this regional data set during different solar activity levels and discusses the different climatological behaviors identified in the ionosphere at these high latitudes. Finally, we will show few examples of typical TEC disturbances observed during extreme solar events. [less ▲]

Single station monitoring of volcanoes using seismic ambient noise

in Geophysical Research Letters (2016)

Seismic ambient noise cross correlation is increasingly used to monitor volcanic activity. However, this method is usually limited to volcanoes equipped with large and dense networks of broadband stations ... [more ▼]

Seismic ambient noise cross correlation is increasingly used to monitor volcanic activity. However, this method is usually limited to volcanoes equipped with large and dense networks of broadband stations. The single station approach may provide a powerful and reliable alternative to the classical “cross-stations” approach when measuring variation of seismic velocities. We implemented it on the Piton de la Fournaise in Reunion Island, a very active volcano with a remarkable multi-disciplinary continuous monitoring. Over the past decade, this volcano was increasingly studied using the traditional cross-correlation technique and therefore represents a unique laboratory to validate our approach. Our results, tested on stations located up to 3.5 km from the eruptive site, performed as well as the classical approach to detect the volcanic eruption in the 1-2 Hz frequency band. This opens new perspectives to successfully forecast volcanic activity at volcanoes equipped with a single 3-component seismometer. [less ▲]

Continuous gravimetric monitoring as an integrative tool for exploring hydrological processes in the Lomme Karst System (Belgium)

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 ▲]

Bilateral comparison between the FG5X-216 and FG5-242

Report (2015)

Relative gravity measurements in Kellyville and Kangerlussuaq in July 2013

Report (2015)

CCM.G-K2 key comparison

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 ▲]

Measurement of the speed-of-light perturbation of free-fall absolute gravimeters

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 ▲]

Accurate Gravimetry at the BIPM Watt Balance Site

in Rizos, C.; Willis, P. (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014)

Future and development of the European Combined Geodetic Network ECGN

in Rizos, C.; Willis, Pascal (Eds.) Earth on the Edge: Science for a Sustanaible Planet (2014)