Towed, active electromagnetic sensor array for on-line terrain mapping of metallic subsurface objects

The safe and effective detection of unexploded ordnance, including mines is a precondition for clean-up and renaturalization of large areas exposed to military training action overlong periods, active combat or other military action. The pulse remanence principle is used for the detection array. A DC current is fed to the transmitter coil via an electronic switch. By this current a magnetic field is built up around the transmitter coil. When the current has reached the steady state, the switch is opened, and the magnetic field decays. By the decaying magnetic field eddy currents are induced in metallic bodies inside the field. These magnetic fields generate secondary magnetic fields decaying slower than the original magnetic field. The secondary fields are detected by a number of receiving coils. Their time dependent output voltages contain information on the the volume, the resistivity and to some extent the shape of the metallic objects.