An electromagnetic geophysical mapping instrument comprising a transmitter and a transmitter coil connected to the transmitter, the transmitter generating intermittent 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 halfsinusoidal waveforms of common polarity. In a time domain instrument, the pulses will typically comprise spaced bursts of immediately successive half-sinusoidal waveforms of the same polarity, whereas in a frequency domain instrument, the pulses will immediately succeed each other and be 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.
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