The HydroGeophysics Group has performed a large SkyTEM survey on Mayotte; a volcanic island between the African mainland and Madagascar. The survey was a part of an extensive investigation carried out by a close collaboration between the French Geological Survey, BRGM, the Mayotte Prefecture and the Aarhus University.

The purpose of the survey was to:

1. Create a geological map of the entire island. The airborne survey provided a full three dimensional picture of the subsurface and therefore it was an efficient tool for guiding the subsequent geological sampling and creation of the geological model.
2. At several locations there was a risk of landslides occurring when the soil gets very wet. It was possible to locate these areas using the survey results.
3. Most of Mayotte’s population is located along its extensive coastline. When the ground water resources are exploited, there is a severe risk that aquifers will be destroyed due to salt water intrusion. Airborne EM is an efficient tool for mapping the salt/fresh water interface.

The technology
The SkyTEM system used in the survey had a transmitter moment of about 100 000 Am2. With this moment the maximum depth of investigation is up to 250m, while different geological layers are mapped right from the surface. The average line separation was 200m but some areas were flown with just a 100m separation. Data were processed while they were flown and the results were then used to optimize the location of the subsequent lines. 

3D image of the island
The field work finished mid-November 2010 and afterwards geophysicists  from the HydroGeophysics Group processed and inverted the data to produce a 3D image of the entire island.

Links
Mayotte island on Wikipedia