Abstract: Method for inverting, in the frequency domain (42), controlled source electromagnetic survey data (41) acquired using a time-division compound waveform made up of sub-sequences of different base waveforms, for example square waves of different frequencies. A windowed Fourier decomposition method is used, with the window size and shape designed in consideration of the sub-sequences. The window length may be twice the length of the compound waveform, or more. Alternatively the window length may be comparable to the sub-sequence length, or slightly less. Window shapes include cos2, rectangular, and triangular. The method addresses the problem of unknown arrival times for each sub-sequence, and also transition transients that occur between sub-sequences.

Abstract: Method for inverting, in the frequency domain (42), controlled source electromagnetic survey data (41) acquired using a time-division compound waveform made up of sub-sequences of different base waveforms, for example square waves of different frequencies. A windowed Fourier decomposition method is used, with the window size and shape designed in consideration of the sub-sequences. The window length may be twice the length of the compound waveform, or more. Alternatively the window length may be comparable to the sub-sequence length, or slightly less. Window shapes include cos2, rectangular, and triangular. The method addresses the problem of unknown arrival times for each sub-sequence, and also transition transients that occur between sub-sequences.