Direction identification of a moving ferromagnetic object by magnetic anomaly

•Identify heading direction only using a single sensor node not sensor network.•The signal phase enables heading directions classification.•A kind of small size, low power and low-frequency search coil magnetometer is developed.•The indicator correctly identifies heading direction at SNR of 9 dB or more against 1/fα noises.•Available saturated data can be utilized for heading direction identification.

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 1 Hz. 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 9 dB 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.