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The study of the abilities of an elm apparatus for shallow depth prospecting necessitates that we analyse the experimental data through theoretical modelling. A 3-D model for a magnetic and a conductivity contrast is presented here. Applied to the Slingram type SH3 case (intercoil spacing equal to 1.5 m and frequency to 8 kHz) it shows that this apparatus is roughly equivalent to the classical Wenner 1 m array and is more sensitive than magnetic prospection to susceptibility changes occurring in the soil above 6 0 cm depth. The 3-D model will also be very valuable for the conception of improvements in the apparatus.
Alain Tabbagh (Mon,) studied this question.