Controlled source electromagnetic (CSEM) methods are sensitive to the subsurface conductivity structure and thus had led to its use in resource exploration. Since the frequency for peak sensitivity and the exact location of an exploration target is normally unknown prior exploration, it is desirable to acquire the received source signal for a broad range of frequencies and in a wide area. Investigations in both directions have been driven by optimising properties of the Fourier transform in order to enhance the frequency range and the detection of the signal for larger source - receiver separations, even though typical issues are intrinsically non stationary such as a floating EM source transmitter on a moving vessel.

We demonstrate on a complete synthetic example that processing of chirped waveform (CWF) signals delivers reliable results and offers improvements like the possibility of longer transmission durations for moving transmitters. With this particular feat CWF can provide longer periods (for more depth penetration) and more data points per period (for more accuracy/robustness in the transfer function estimation) compared to e.g. a squared wave or a broad band ternary waveform.


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