Measuring the waveform of time domain AEM systems using a ground loop

SUMMARY Measurement of the current waveform of time domain AEM systems which possess coincident-loop receivers can be problematic due to the high moment of the transmitter loop during the on-time. We present a simple method of measuring the transmitter current waveform by measuring the current induced in a closed, accurately laid out and surveyed multi-turn, insulated ground loop of known inductance L and resistance R. The current induced in the ground loop, measured by a 24-bit A/D converter capable of sampling at 96 kHz, is the convolution of the time derivative of the transmitter current waveform with an exponential decay of time constant equal to the L/R ratio of the wire loop. With an understanding of the A/D converter measuring the ground loop response, the transmitter waveform can be deconvolved from the ground loop decay.