Signal processing approaches to obtain complex resistivity and phase at multiple frequencies for the electrical exploration method

The electrical method is an effective geophysical exploration method. Complex resistivity and phase at multiple frequencies can be obtained simultaneously by transmitting pseudo random signal current (2ⁿ-sequence or m-sequence). However, with the development of industry, electromagnetic (EM) interference has been a challenging problem to the transmitted signal, including noise interference and EM coupling. This article describes the application of several simple and effective signal processing approaches to improve the data quality for the electrical method. For the problem of noise interference, a robust statistical method was studied. In addition, coherence analysis between current data and potential data was applied to extract data with high signal-to-noise ratio. For EM coupling interference, a relative phase spectrum was used to remove coupling interference in the complex resistivity phase and an inverse differential operation was adopted to correct amplitude spectrum. We demonstrated the effectiveness of our processing approach by showing examples of data acquired in a noisy survey area for electrical prospecting. Compared to common methods, these processing methods can suppress EM interference effectively and do not lead to signal distortion. These approaches can be considered for data processing in electrical prospecting.