Abstract: A frequency domain electromagnetic geophysical mapping instrument has a transmitter, a transmitter coil connected to the transmitter, the transmitter generating current pulse waveforms formed by half-sinusoidal output waveform segments of a waveform having a frequency equal to a resonant frequency of the transmitter coil, and a receiver, in which the transmitter generates current pulses including pulses comprising a plurality of immediately successive half-sinusoidal waveform segments of common polarity. The pulses immediately succeed each other and are of alternating polarity. The pulse lengths may in this case be equal, or vary in a manner providing a desired output spectrum, for example according to a pseudo-random sequence.

Abstract: A method is disclosed for discriminating electromagnetic responses of metallic objects in soil to application of an electromagnetic pulse from superposed responses due to magnetic susceptibility of the soil, comprising substantially eliminating, from at least a portion of the response, any component having a power law decay characteristic with an exponent which is characteristic of the soil.

Abstract: In a time domain electromagnetic mapping technique of the type using transmitter pulses of half-sinusoidal waveform, with the half sinusoids being segments of a sinusoidal waveform having a frequency and corresponding to a resonant frequency of the transmitter coil, an improved current fall time at the end of each pulse is obtained by forming each transmitter pulse of plural immediately successive half sinusoids, the transmitter coil being tuned to an appropriately increased resonant frequency relative to the pulse repetition rate. Circuits for generating the improved pulse waveforms are disclosed.