First analyses of the iOSG-type superconducting gravimeter at the low noise underground laboratory (LSBB URL) of Rustrel, France

Abstract

Abstract.In the last few years, the performance of the cryogenic gravity instruments has been further improved by the development of a new generation of superconducting gravimeter (SG): the so-called iOSG which is a superconducting gravimeter designed for observatory purpose with a heavier sphere than previous SGs. The first iOSG (iOSG-024) has been installed in July 2015 at the LSSB low background noise underground research laboratory in Rustrel (France), funded by the EQUIPEX MIGA (Matter wave-laser based Interferometer Gravitation Antenna) project and by the European FEDER 2006-2013 "PFM LSBB -Développement des qualités environnementales du LSBB". This instrument is operational since September 2015. We present the first tidal analyses of the 7-month time-varying gravity records of this newly installed instrument as well as the calibration results performed by parallel FG5 absolute gravity measurements. We also show the performances of iOSG-024 in terms of noise levels in the seismic (in the millihertz frequency range) band using a standardized procedure based on the computation of the residual power spectral densities over a quiet time period. The obtained noise levels are compared with other SG sites and with seismological reference noise models. The combination of the instrumental performance of the iOSG with the LSBB site properties makes this gravimetric station one of the quietest in the world, comparable to the lower sensor of the OSG-56 at BFO, at seismic frequencies.

Exploring gravity with the MIGA large scale atom interferometer

“…Figure 10 -right shows a recent measurement of the noise level at LSBB, compared with the curves obtained in Strasbourg (France) and at the Black Forest Observatory (Germany). The instrument installed at LSBB has a noise performance among the best in a worldwide network of superconducting gravimeters 91 , 92 , with an amplitude spectral density of 1.8 nm·s −2 ·Hz −1/2 at 1 mHz. Notably, superconducting gravimeters have a characteristic noise lower than the Earth’s background noise at frequencies below 1 mHz 93 , and permit thus to study low-frequency seismic and sub-seismic modes.…”

Intercomparing Superconducting Gravimeter Records in a Dense Meter-Scale Network at the J9 Gravimetric Observatory of Strasbourg, France

“…In contrast, the iGrav, which was designed for field use, is easier to move and operate at remote sites (Warburton et al, 2011 ). The iOSG23 was installed at J9 in January 2016 and is the second iOSG installed in France; the first one was iOSG24 installed in July 2015 at the low background noise interdisciplinary ground and underground based research laboratory LSBB of Rustrel, in the south of France (Rosat et al, 2016 ). Only three iOSGs have been manufactured and the third, iOSG22, was installed at Metsähovi Geodetic Fundamental Research Station (ME), Finland in December 2016.…”

“…After operation at J9, iGrav30 was moved to the Strengbach catchment in the Vosges mountains (at 70 km from Strasbourg) end of June 2017 and iGrav31 was moved in May 2019 to the surface station at LSBB ( https://lsbb.cnrs.fr ) in South of France. iGrav30 is used to investigate the water storage changes at the catchment scale (Chaffaut et al, 2020 ), while iGrav31 establishes together with iOSG24 (the twin meter of iOSG23 studied here) a differential gravity experiment that will be very useful to locate the underground water mass changes already detected by iOSG24 alone (Mouyen et al, 2019 ; Rosat et al, 2016 , 2018 ). The eight SGs were installed in different rooms of the J9 bunker as illustrated in Fig.…”

Vestale loop: a robust, versatile, reliable and remote controlled bench for environmental magnetic sensing at hectometric scale

“…The Hypermagneto scientific project consists in the instrumentation of Vestale to make it both a magnetic excitation source and a standalone environmental sensor, by improving the way it can be connected to scientific instruments. In a first approach, the underlying idea is the corellation of the measurements produced by such an unusual device, with different kinds of measurements existing on site as for instance gravimetry [2] or electromagnetic survey [3,4]. The experimental developement of the measurement bench is already done, making it possible to monitor the electrical characteristics of the coil or to use it as a passive giant magnetic antenna.…”