Calibration and Alignment of Tri-Axial Magnetometers for Attitude Determination

Ellipsoid fitting method is frequently used to calibrate tri-axial magnetometer in navigation systems, but it cannot ensure the alignment between the sensor triad and the coordinate system of the host platform. This paper presents a novel calibration method to overcome this shortcoming. When the sensor triad is rotated around a selected axis, the projection of geomagnetic vector onto this axis should be constant. On the other hand, the angle between geomagnetic vector and gravity vector is also constant. These two phenomena can be described by inner product mathematically. Either of these two constant inner products can he utilized with the constant norm of geomagnetic vector to form the proposed dual inner product method, in order to solve the 12-parameter error model of tri-axial magnetometer. Simulations and experiments prove the effectiveness and robustness of the proposed method. It can achieve reference-free calibration and alignment of tri-axial magnetometer, and help to enhance the accuracy of attitude determination based on geomagnetism.