Magnetic Inversion under Remanent Conditions Using Equivalent Layer Direction Estimation and VOXI Earth Modelling

Abstract

Remanent magnetisation is a critical challenge in magnetic interpretation, often leading to mispositioned anomalies and unreliable inversion results when neglected. This study applies and validates a practical, sequential two‑step workflow that integrates existing techniques to improve magnetic modelling in scenarios where remanent components significantly influence the anomaly geometry. In the first stage, the total magnetisation direction is estimated using the Equivalent Layer technique, which reconstructs the effective magnetisation vector from the observed anomaly without decomposing it into induced and remanent components. The magnetisation direction estimated via the equivalent layer technique was used to perform the reduction to the pole (RTP), and the inversion was subsequently carried out assuming a vertical inducing field (D = 0°, I = 90°). The methodology was tested on synthetic models with varying remanent contributions to evaluate its performance in controlled conditions. Results demonstrate that incorrect directional assumptions lead to distorted source geometries and underestimated susceptibilities, whereas using the Equivalent Layer estimated direction significantly improves inversion accuracy. The approach was also applied to a real airborne magnetic dataset from Espírito Santo State, Brazil, where it successfully recovered a westward‑dipping magnetic body with coherent susceptibility structure. Residual analysis confirmed strong agreement between predicted and observed fields, reinforcing the method’s robustness. While the current implementation assumes a constant magnetisation direction within the target volume, making it less suitable for geologically complex bodies, it offers a stable and interpretable solution for cases where remanence is spatially coherent. This study provides a practical, reproducible workflow for the integrated application of EL‑based direction estimation, RTP, and VOXI susceptibility inversion to remanence‑affected datasets. This workflow is compatible with standard modelling platforms and provides a practical reference for remanence‑affected magnetic interpretation.