geophysical imaging

The bulk of the activity is to provide the technical support needed for the scientific projects carried out within the Geophysical Imaging group in the DIMENV team.

Electrical impedance tomography (EIT) device between boreholes

Research topics

Several focal areas have been developed in the laboratory and directly involve the technical department. Two main approaches are followed:

  • methodological developments and measurements in an acoustic tank on complex interfaces (granular media, rough interfaces, etc.).
  • the design and production of instrumental devices in the laboratory for implementation in the field (Mont Terri underground laboratory, Soufrière volcano in Guadeloupe, bed load transport in rivers, Guidel hydrogeological site, etc.).

Major technical developments were necessary to carry out these projects, so as to be able to meet the conditions of in situ applications:

  • in the Mont Terri laboratory, implementation of a seismic endoscope(this project resulted in the drafting of a scientific and technical report).
  • manufacture of a network of acoustic (64 pre-amplified channels) and electrical antennae (64 electrodes).
  • manufacture of an antenna to measure the spontaneous electrical potential (80 non-polarizable electrodes).
  • adaptation of an acoustic source for measurements in horizontal boreholes.
  • adaptation of a low frequency seismic source.
  • development of a multi-frequency measuring system for complex electrical impedance.
  • monitoring of seismic signals over several years in one of the tunnels of the Mont Terri laboratory
  • on the Soufrière volcano: ANR Domoscan and then Diaphane, technical developments of devices to take acoustic measurements in acid/high temperature environments -adaptation of geophones for seismic acquisitions in hostile environments-temperature measurements- manufacture of muon telescopes (collaboration with The Institute of Nuclear physics of Lyon (IPNL)).
  • construction of a device to automatically measure complex electrical impedance in boreholes to continually monitor the water saturation of the soil.
  • experimental characterization of the physical properties of air bubbles in an underwater environment, adaptation of a compressed air source to generate bubbles.
  • production of a device for heat transfer measurements in a granular medium.

To complete these technical achievements, and in order to control the measurement devices via computer it was necessary to write acquisition codes, especially for the transmission/reception of acoustic signals in tanks with motor movements and for tomography and acoustic transmission measurements at Mont Terri.
Through these projects, several complementary pieces of equipment were acquired with, among other things, the acquisition of sensors and hydrophones (directional/omnidirectional, several frequency ranges, etc.), a broadband power amplifier, several acquisition cards dedicated to the various measurement configurations. The work initiated during the ANR Stabingram project was used for the technical development of an acoustic backscatter measurement requiring the implementation of a transmission/reception system on a track combined with an angular motorized device.
A waterproof linear table was acquired for the acoustic characterization of submerged complex interfaces (destabilization of granular media, turbulent interfaces).
Furthermore, this equipment has enabled a collaboration with Ifremer for the Vp/Vs measurement tests in controlled granular media and the experimental characterization of the physical properties of air bubbles in underwater environments.

Detection of avalanche precursors - © Geophysical imaging