Real-Time Localization of Magnetic Target Using Second-Order Scalar Magnetic Gradients

Magnetic anomaly generated by magnetic target is widely used in many areas. In this paper, a real-time magnetic target localization method based on second-order scalar magnetic gradients at the closest point of approach (CPA) is proposed. By exploiting the geometric symmetry of the magnetic anomaly field at the CPA point, closed-form expressions of the target position and magnetic moment are derived directly from the second-order spatial derivatives of scalar magnetic anomaly under the induced-magnetization assumption, thereby avoiding iterative global optimization. Furthermore, a residual-based error index is constructed to evaluate the consistency between measured and reconstructed second-order scalar magnetic gradients, enabling automatic determination of the CPA point during platform motion. The proposed method is validated by the experiment. The results show that the CPA point on the trajectory can be accurately identified using the proposed error index, and the localization accuracy is significantly improved near the CPA point. At the CPA point, the relative errors of the estimated distances and angles between the target and the two sensors are 0.89% and 0.38%, and 1.0% and 0.52%, respectively, while the relative error of the estimated magnetic moment magnitude is 4.85%. Therefore, the proposed method has great value in target localization based on a mobile magnetic anomaly detection system.