Direction identification of a moving ferromagnetic object by magnetic anomaly

Abstract

We propose a novel method for identifying heading direction of a ferromagnetic target by processing magnetic measurements of two directions. The proposed method relies on the phase of the complex signal composed of two dimensions (2-D) magnetic anomaly signals accessed by two perpendicularly placed sensing units. Theoretical analysis based on a magnetic dipole model shows the derivative of phase of the composed complex signal can indicate the heading direction of a moving ferromagnetic object, no matter what the target magnetic moment magnitude and orientation are. Given flexibility and power savings of the measurement systems, a kind of small size, low power and low-frequency search coil magnetometer is developed as sensing units with the equivalent noise level of approximate 12 pT/Hz at about 1Hz. Computer simulation and real-word experiments have been conducted to test the performance of the method. The results show that the algorithm can identify the heading direction correctly at SNR of 9dB or more against 1/fα noises. Furthermore, the method can classify the direction with available saturated data. The simple implementation and low-computational complexity make the proposed method a potential candidate for real-time underwater area passive surveillance.