dGNSS

The LMV has differential GNSS equipment from TopCon (off-line only) and Trimble (very recent and full RTK) brands. The accuracy of these devices can reach the millimeter. They are used for various types of measurements ranging from micro-topography to the positioning of other geophysical devices for field measurements or rock sampling. In this case, the accuracy allows for 2D and 3D tomography and inversions.

Study of the electrical resistivity of volcanic edifices

The electrical resistivity of volcanic rocks can vary by several orders of magnitude depending on their water saturation, temperature, presence of mineralised fluids or clay minerals. The distribution of resistivities at depth can therefore be interpreted in terms of geological structure. This distribution can be studied by different electrical and electromagnetic methods. The LMV has two types of equipment: intruments to carry out direct surveys and 2D tomographiy and a light equipment offering the capacity to carry out electromagnetic drilling with an investigation depth of up to a few hundred metres.

2D direct current tomography

The equipment includes :

• ABEM TERRAMETER SAS4000 Resistivity Meter
• ES1064 addressing box, for 4 channels
• 16 cables, 4 outputs with 40 m distance between each output, on Schill reels, 160 m / cable
• 8 Cables, 8 outputs with 20 m distance between each output, on Schill reels, Lg 160 m / cable
• Cable kit « Standard – 5 m », 16 outlets with a distance of 5 m between them. 4 SCHILL reels,
• 2 Cables, 32 outlets with a distance of 2 m between each outlet, on Schill reels, Lg 64 m / cable
• RES2DINV interpretation software

This equipment is shared with the GeoSciences Reunion Laboratory of the University of Reunion.
Its originality is a unique line of 64 electrodes separated by 40 m. This line of 2560 m allows the acquisition of a 2D image of the resistivity distribution between the surface and 400-500 m depth.

3D direct current tomography

Recently acquired as part of a European CAPRICE programme, the equipment includes:

• An I-FullWeather injector from IRIS instrument and 20 sensors;
• a regulated generator;
• over 8km of cable for the infinite electrode;

Time Domain ElectroMagnetism (TDEM) probes

Our equipment includes :

• « 48 channel TEM-FAST 48HPC system with antennas, calibration unit and acquisition software.
• TEM-RES software for data analysis and inversion.
• iPAQ PC.

TDEM electrical resistivity measurements on Yasur volcano (field acquisition and resistivity section)