Interpretation of controlled-source electromagnetic data from iron ores under rough topography

• We have developed a 2.5D inversion algorithm which rigorously incorporates topography.
• The magnetic effect of an iron ore in our field conditions was investigated.
• We successfully carried out 2.5D EM inversion of the field data.

This paper describes a study of the interpretation of controlled-source electromagnetic (CSEM) data obtained from iron ores under rough topography. For the accurate interpretation of the data, we considered two characteristics that affect the CSEM data; one is rough topography and the other is an iron ore. We have developed the 2.5D inverse modeling algorithm, which rigorously incorporates topography, based on the finite element method (FEM) for excluding erroneous interpretations from rough topography. Before applying the developed algorithm to the field data, we demonstrated that rough topography distorts the resistivity value or distribution of anomalies through numerical experiments. In addition, we investigated the effect of magnetic susceptibility by an iron ore on the data under the field conditions through numerical simulation. Because a magnetic anomaly exerted less influence on the quadrature component of the data in a numerical test, we confirmed that the inversion of the quadrature component of the field data, by considering only conductivity, is reasonable. Based on these results from the consideration of two characteristics of the field, we successfully carried out inversion of the field data. A comparison of the result of the CSEM inversion with a priori information of the field, verified the reliability of our inversion result.