Robust Attitude Estimation Method For Underwater Vehicles with External and Internal Magnetic Noise Rejection using Adaptive Indirect Kalman Filter

This paper considers the question of measuring attitude using magnetometer-equipped Inertial Measurement Units (IMUs) when in the presence of magnetic disturbance. Specifically, for use in micro-observational class underwater vehicles. Such vehicles' small size and mobility suit activities in coral reefs but often face significant magnetic interference due to high metal debris content, especially in artificial reefs. Their small size also means motor thrusters are situated closer to the magnetometers, producing additional interference. An Adaptive Indirect Kalman Filter is proposed that uses IMU and motor speed measurements to deal with two main sources of disturbances: magnetic fields from foreign objects, and from the vehicle's own motors rotating in slow speed. The method has been evaluated using a custom underwater vehicle made in HKUST, and results show that the proposed method is able to obtain accurate orientation representations even when approaching objects with strong magnetic fields or when the motors are producing interference by rotating in slow speeds.