Extraction of targeted source information from superimposed magnetic anomalies
Authors: Zhu Dan , Hu Xiangyun , Liu Shuang 
Published: February 2023

&#160; &#160; Magnetic anomalies commonly contain anomalies generated by crustal rocks that have variable mineral compositions and natural remanent magnetizations. Understanding the magnetic susceptibility, remanent magnetization, magnetization direction, and distribution is important for studying the spatial location, formation, and evolution of underground rocks. However, superposition of magnetic anomalies leads to nonnegligible errors of inversion and interpretation. To overcome the interpretation problems caused by source interference, it is necessary for the target magnetic anomaly to be extracted from the observed magnetic anomaly data. Different methods have been developed to separate the magnetic anomalies of different sources using the spectral differences of regional and residual anomalies. Such methods, which include matched filtering, Wiener filtering, and wavelet analysis, have been successfully applied to solve many geological problems. However, these methods cannot extract the anomalies caused by the interference of sources at similar depths because the spectra of the target and residual magnetic anomalies are similar. Effective techniques to obtain additional magnetic information regarding the distribution of rocks at different layers and with different magnetization directions remain lacking.&#160; &#160; Unlike existing regional-residual separation methods used for separating superimposed magnetic anomalies caused by sources with a large depth separation, this study focuses on magnetic anomalies generated by variability of the magnetic parameters and source interference with and without depth differences. We propose a new and useful method for extracting a target magnetic anomaly from an observed magnetic anomaly field. An optimization scheme is proposed for approximating the low-rank component of an observed magnetic anomaly field on the basis of low-rank theory. The magnetic dipole layout is added as a constraint based on the assumed source location. The optimal magnetizations of the magnetic dipoles are then obtained to minimize the objective function. The sum of the magnetic anomalies generated by the magnetic dipoles is calculated as the target magnetic anomaly. The synthetic and field data experiments indicate that the proposed method can accurately and robustly recover target magnetic anomalies. In the field data experiments, the magnetization information of the various isolated sources is derived via 3D fuzzy C-means inversion using the extracted magnetic anomalies. The results show that the proposed method can extract the geometric and physical information of each target magnetic source, even when the observed magnetic anomaly field is generated by various superimposed sources with target source interference at similar depths. The proposed method has the potential for dealing with the separation problems of potential field data with different scales, including the separation of the geomagnetic core field and the lithospheric magnetic field as well as the extraction of target magnetic anomalies from satellite magnetic measurements. Therefore, this approach could be of great importance for geological investigations and mineral exploration.