Heliborne geophysical acquisition using electromagnetic and magnetic methods
© Alexandre Magnan
The French Ministry for the Ecological Transition and Territorial Cohesion has commissioned BRGM, the national geological survey, to conduct an airborne campaign to acquire geophysical data over the Vosges and Lyonnais mountains during the summer and autumn of 2024. Intended to further geological knowledge of the areas covered, these latest campaigns continue the series of flights begun in 2022 in the western part of the Massif Central.
Two heliborne campaigns will carry three different instruments for surface and subsurface imagery. The helicopters will not fly over built-up areas, and the surveys will have no impact on the environment or public health. The campaigns will make it possible to acquire several homogeneous and coherent data sets simultaneously over a large area, including terrain that is hilly or difficult to access.
Helicopter geophysical survey using magnetic and gamma-spectrometry methods
© BRGM
The purpose of this survey is to study the Vosges and Lyonnais mountains using non-invasive methods (specifically magnetic, gamma spectrometry and electromagnetic methods). The information acquired will provide a better understanding of the specific physico-chemical properties of the soil and rocks, from the near-surface (gamma-spectrometry) to a depth of several hundred metres (electromagnetic method), or even several kilometres (magnetic method).
This data will then be processed to image the nature and structure of the regional subsoil and thus further geological knowledge. Ultimately, this work should help us to better characterise underground resources (hydrological, geothermal or mineral) and to better assess natural hazards such as seismicity, clay shrinkage and swelling, and landslides. The data resulting from these surveys will be public and accessible to all stakeholders for purposes of resource development or exploitation.
Several weeks of surveys
Divided equally between the Vosges and Lyonnais mountains, the campaign totals over 25,000 km of heliborne surveys using the magnetic and gamma-spectrometry methods, and 5,000 km using the electromagnetic method.
For the Lyonnais mountains, the acquisition campaigns will cover an area bounded to the west by Roanne and to the east by the Rhône Valley (from Belleville en Beaujolais to Saint-Rambert-d'Albon).
For the Vosges, campaigns will focus on an area bounded to the east by Strasbourg, Colmar, Belfort and Héricourt and to the west by Epinal.
Operations will begin in July and will last between three and six weeks in each sector.
Areas covered by airborne geophysical campaigns using magnetic/gamma spectrometry methods (black) and electromagnetic/magnetic methods (blue) - in the Vosges (left) and Lyonnais mountains (right).
© BRGM
