Measured electromagnetic fields in marine controlled source electromagnetic (CSEM) method always have some uncertainties to some extent. One is the structure in the subsurface and the other is the source signature that could have uncertainties due to the environmental conditions around the source. We hypothesized that the perturbation in the source waveform would be estimated using the backpropagation of anomalous electric fields and tested the hypothesis. We first developed an electromagnetic full waveform inversion that could deal with both the conductivity of the subsurface and the source waveform simultaneously. We compared the simultaneous inversion with a conventional inversion for a synthetic data. The synthetic example shows that even if the amplitude of an initial source waveform is erroneously underestimated with 5 % smaller than true source waveform, we could estimate the source waveform employing this simultaneous inversion algorithm. We also find that the obtained conductivity structure of the subsurface from the simultaneous inversion is appropriate than that from the conventional inversion. From numerical results, we conclude that it is realizable to estimate the unknown perturbation of the source parameters.
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