Frequency-domain controlled-source electromagnetic surveys can be negatively affected by near-surface geologic features, resulting in static shifts in the observed electric field amplitude data. We propose using an equivalent source method to denoise electric field data from frequency-domain controlled-source electromagnetic (CSEM) surveys. The equivalent source method can either be applied individually to data from each measured frequency or simultaneously to data from all frequencies measured. We demonstrate the effectiveness of the method by denoising an individual synthetic CSEM survey with data contaminated with noise from near-surface conductive bodies, as well as a synthetic time-lapse survey representing resistivity changes in a target due to, for instance, CO2 sequestration. We also apply the equivalent source method to denoise a set of controlled-source audio-magnetotelluric data affected by static shift from a field survey in western China.

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