Mini-SkyTEM:A new airborne transient EM system for near-surface aquifer mapping

The SkyTEM system is being developed for almost ten years in Denmark and has been specially designed for the groundwater mapping. Through the years more and more early gates are becoming interpretable, and for almost two years gates below 10 µs have been used generically. The electronics and processing developments end recently with the new Mini-SkyTEM system which provides a first gate at 5-6 µs. This new system can also be flown up to a speed of 140 km/h, allowing a same coverage at a lower cost compared to the larger systems. The first pilot survey of the new Mini-SkyTEM was flown in June 2011 inside the NiCA project where the purpose is to model the oxydo-reduction of the nitrates in the near-surface aquifers for pollution management. Despite its very low transmitter moment, the Mini-SkyTEM system provides a depth of investigation of 100 m considering a mean resistivity of 50 Ωm. But more importantly, a good correlation between the resistivity boundaries and the geological interfaces defined in the borehole logs is observed in the upper 20 m. This gives us confidence in the future use of this transient airborne EM system for the mapping of the very near-surface aquifers.