Improving knowledge of the subsurface for better water management
Faced with the effects of climate change, changing uses and increasing demands, it is essential to develop our knowledge of groundwater resources. With this in mind, several heliborne geophysical campaigns are currently being carried out in various regions of France.
Using measurements taken from a helicopter fitted with an antenna, scientists can obtain a 3D image of geological layers down to a depth of around 300 metres without coming into direct contact with the ground. This data, combined with geological and hydrogeological observations, provides a better understanding of how groundwater circulates.
Whether for studying the hydrogeology of the major valleys in the Pyrenees, anticipating the effects of climate change on a Normandy catchment area, learning more about water circulation in the Vosges mountains, or assessing the salinisation of coastal aquifers on the Hauts-de-France coast, these campaigns all have the same objective of improving our knowledge of groundwater so that we can better manage the resource.
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Start of a heli-borne geophysics campaign in the Pyrenees
In these three major Pyrenean valleys, vast sedimentary layers up to several hundred metres thick were formed as a result of intense erosion following the major warming of the climate some twelve thousand years ago. Still poorly understood, these layers of post-glacial sediment could contain significant water resources, the mechanisms of which have yet to be studied. To characterise the quantities involved and improve knowledge of their hydrogeological characteristics, the Haute-Garonne departmental Council, together with the Adour-Garonne water agency, the Occitanie region, the Ariège and Hautes-Pyrénées departmental Councils and BRGM, are launching a research programme scheduled to last four years.
The aim of this project is to develop a geological model of the deposition of sediments that have filled the Garonne valley since the last ice age. The model will help determine the locations of the most likely targets to be explored and it should be possible to extrapolate the data to other valleys in the Pyrenees. Moreover, the nature of these aquifers and the conditions under which they are recharged with water will be studied, in particular by drilling exploratory boreholes.
A helicopter will be flying over the valleys during a two-week period
The first stage of the project will involve aerial investigation of the subsurface. From 7 October, for a planned two-week period, a helicopter chartered by the Danish service provider SkyTEM will be flying over several Pyrenean valleys in the départements of Haute-Garonne, Ariège and Hautes-Pyrénées. It will carry a 20 m diameter transmitter loop for remote sensing of the subsurface.
Airborne surveys do not fly over built-up areas, have no impact on the environment or health and quickly provide a continuous view of the subsurface, as a map or in a 3D format, regardless of land use. The helicopter-borne survey will detect differences in electrical resistivity in the subsurface. The data acquired will undergo specific processing with a view to its interpretation. Ultimately, the measurements, coupled with geological and hydrogeological observations, will enable scientists to image the geometry and structure of the geological layers to a depth of around 300 metres, providing key information for understanding water flows.
This helicopter geophysical survey campaign will total 800 km of flight lines and will focus on the Garonne, Nestes (Aure and Louron), Gave de Pau and Ariège valleys.
Hauts-de-France: a heliborne geophysics campaign along the coast
Map showing airborne survey routes over the study site.
© BRGM
Intensive exploitation of coastal groundwater, combined with a rise in mean sea level and disturbance caused by erosion of the coastline, can lead to an increase in groundwater salinity. However, there is currently no basin-wide monitoring network for the salinisation of coastal water bodies in the Artois-Picardy basin. This is why the Agence de l'eau Artois-Picardie (Artois-Picardy Water Agency), the project owner, and BRGM are working together on a scientific project, AquaSEL, to describe, monitor and understand changes in the salinisation of coastal aquifers in the Hauts-de-France region.
More specifically, the aim of the 4-year project is to create or refine existing geological models of the coastal subsurface, in order to set up a hydrogeological aquifer-monitoring network to understand how they work, as well as the origins and evolution of the salinisation of this water, so as to be able to propose the most appropriate measures to limit groundwater being affected by it. The final report on the project should be available by the end of 2026.
Improving knowledge of coastal aquifers
Within this framework, significant efforts are being made to compile existing data on coastal geology and hydrogeology.
In order to acquire new data where information is scarce or scattered, the project scientists are carrying out numerous investigations throughout the coastal zone. In addition to the fieldwork of hydrogeologists locating boreholes or wells to measure salinity, and the field work of geologists observing cliffs and the sides of quarries, geophysicists are adding acquisition campaigns, on the ground with a towed vehicle and in the air with a helicopter. In particular, at the end of October 2025, a week-long airborne geophysical campaign will be conducted along the coastline. A helicopter, chartered by the Danish airborne-geophysics company, SkyTEM, will be flying over several communes in the Hauts-de-France region. It will carry a 20 m diameter transmitter loop for remote sensing of the subsurface. This type of investigation is both rare and innovative.
Heliborne geophysical surveys quickly provide a continuous view of the subsurface. The aim of these heliborne surveys is to identify electrical resistivity contrasts in rock formations. Ground-based geophysical acquisitions will then provide complementary data, and all the new data will be cross-referenced with geological, hydrogeological and hydrogeochemical observations. Thanks to this information, scientists will be able to image the geometry of geological layers and the faults that affect them, down to 300 metres in depth. They will also be able to characterise how seawater mixes with freshwater in aquifers. These multidisciplinary interpretations will provide significant information to further geological knowledge and improve groundwater management.
This heliborne geophysical survey campaign will cover a total of 150 km of flight lines along the coast between Le Report and Calais. It will not fly over built-up areas and will have no impact on the environment or public health.
In Normandy, a campaign to find out more about groundwater resources in the Iton basin
BRGM and the Syndicat Mixte d'Aménagement du Bassin de l'Iton (SMABI) are launching a heliborne geophysics campaign over part of Normandy. This operation is part of a study to determine the "volumes that can be abstracted" aimed at preserving water resources and anticipating user conflicts. The Iton basin, recognised as a strategic resource for the supply of drinking water, is the subject of an ambitious four-year scientific programme.
Between 23 and 29 October 2025, a helicopter chartered by the Danish airborne-geophysics company, SkyTEM, will fly over several communes in Normandy. It will carry a 20 m diameter transmitter loop for remote sensing of the subsurface.
Airborne surveys do not fly over built-up areas, have no impact on the environment or public health and quickly provide a continuous view of the subsurface, as a map or in a 3D format, regardless of land use. The heliborne survey will detect differences in electrical resistivity in the subsurface. The data acquired will undergo specific processing with a view to their interpretation. Ultimately, the measurements, cross-matched with geological and hydrogeological observations, will enable scientists to visualise the geometry and structure of the geological layers to a depth of around 300 metres, providing key information for understanding groundwater flows.
Better anticipating the effects of climate change
This helicopter geophysical survey campaign will cover a total of 300 km of flight lines and will focus on the Iton catchment area as well as a long stretch between Évreux and Le Tréport. It should determine more precisely the volumes of groundwater available, including the direction and velocity of flow, and enable development of a 3D mathematical model to facilitate future management according to different climate scenarios.
In addition to this heliborne geophysical operation, quantitative and flow measurement campaigns will supplement the BRGM hydrogeological model for the MORITO project and the study to determine the "volumes that can be abstracted". All in all, the project should provide a better understanding of the exchanges between the aquifer and the river and improve water management for future generations.
Vittel-Contrexéville: an unprecedented airborne campaign in the Vosges
Location of the study area around Vittel and Contrexéville (88) and provisional flight plan.
© BRGM
The Research and Development (R&D) agreement signed in April 2023 between the Vosges Département (CD88) and BRGM, with funding from the Rhine-Meuse Water Agency, aims to implement a Water Resources Observatory of the area covered by the Schéma d'Aménagement et de Gestion des Eaux des Grès du Trias Inférieur, named SAGE GTI (Master plan for development and management of the Lower Triassic sandstone aquifer), within 4 years (2023 to 2027).
The scientific programme includes a number of actions, all designed to improve our understanding of how groundwater flows and its links with surface water, to create a multi-aquifer model based on the pre-existing model for the Lower Triassic sandstone aquifer (GTI) and to design a platform for disseminating information and sharing tools to help manage water resources for current and future needs.
Against this backdrop, and in order to improve the knowledge of the subsurface needed to design a hydrogeological model, the GTI SAGE Observatory is launching a helicopter geophysics campaign in the Vittel and Contrexéville area. This study will focus in particular on already known fault zones and will cover a total 400 km of flight lines.
A helicopter will be flying over the Vosges for a week
Starting in October 2025, a helicopter chartered by the Danish airborne geophysics company, SkyTEM, will fly over a number of communes around Vittel and Contrexéville for an estimated period of one week. It will carry a 20 m diameter transmitter loop for remote sensing of the subsurface.
The helicopters will not fly over built-up areas, and the surveys will have no impact on the environment or public health. They will quickly provide a continuous view of the subsurface, in map or 3D format, regardless of land use. The airborne survey will detect differences in electrical resistivity in the subsurface. The data acquired will undergo specific processing with a view to its interpretation. Ultimately, the measurements, combined with geological and hydrogeological observations, will enable scientists to visualise the geometry and structure of the geological layers to a depth of around 300 metres, providing key information for understanding groundwater flows.
frequently asked questions
Why is this airborne survey being undertaken?
To improve knowledge of the subsurface around Vittel and Contrexéville, gain a better understanding of groundwater circulation and help with sustainable management of the resource as part of the SAGE GTI Hydrogeological Observatory.
What does the helicopter measure?
Physical signals: transient electromagnetic fields, the Earth's magnetic field and/or natural gamma radiation. These measurements are said to be non-invasive and allow the subsurface to be imaged; they do not produce photographs.
Will photos or private data be taken?
No, airborne acquisition is carried out over non-built-up areas. The sensors do not acquire images or personal data. The results are published as geophysical maps (showing physical properties of the subsurface).
Is there an impact on public health?
No, the transmitter loops emit low frequency, non-ionising fields, following strict protocols. There is no overflight of built-up areas, and the flight is short.
Will the noise be a nuisance?
The rotor noise is temporary: the helicopter only passes overhead on each flight line (for a few seconds). The campaign is scheduled to last 2 to 3 days, subject to weather conditions.
Will the helicopter fly over towns?
No, the helicopter will not fly over built-up areas. Trajectories and altitudes are clearly laid out in the flight authorisations.
What permits are required for the operation?
Flights are carried out with authorisation from the civil aviation authorities and prefectures, for a precisely defined period, aircraft and routes.
Where can I consult the results?
The geophysical data will be processed and turned into maps. They will be made available via the BRGM, SAGE GTI and Département des Vosges websites as the project progresses.
