Shaping Optimal Transmitter Waveforms For Marine CSEM Surveys

A much used transmitter waveform for marine CSEM surveys is the square wave. The square wave has the advantage that maximum energy is transferred to the subsurface, since the transmitter current is running at it’s peak amplitude at all times. The problem with the square wave is that it has a less than ideal frequency spectrum. The frequency domain current amplitudes are proportional to the inverse of frequency, so the amplitudes are reduced with increased frequency. At the same time the absorption of the electromagnetic field increases with frequency. We propose a waveform where the transmitter operate at its peak current at all times, but where the number of switching times within a period may be larger than two, which is the number of switching times per period for a square wave. The method is based on matching desired frequency spectra with spectra obtained from generalized square waves. This is an optimization problem that is solved with a Monte Carlo method. The end results are waveforms that can be used for an electric dipole transmitter and where the frequency spectra are close to predefined desired spectra.