magnetic calibration of three-axis strapdown magnetometers for applications in mems attitude-heading reference systems

in a strapdown magnetic compass, heading angle is estimated using the earth's magnetic field measured by three-axis magnetometers (tam). however, due to several inevitable errors in the magnetic system, such as sensitivity errors, non-orthogonal and misalignment errors, hard iron and soft iron errors, measurement noises and local magnetic fields, there are large error between the magnetometers' outputs and actual geomagnetic field vector. this is the necessity of magnetic calibration of tam, especially in navigation application to achieve the true heading angle. in this paper, two methodologies, including clustering swinging method and clustering velocity vector method are presented for magnetic compass calibration. several factors for clustering process have been introduced and analyzed. the algorithms can be applied in both low-cost mems magnetometer and high-accuracy magnetic sensors. the proposed calibration algorithms have been evaluated using in-ground and in-flight tests. it can be concluded from the experimental results that, applying the clustering calibration algorithms bring about a considerable enhancement in the accuracy of magnetic heading angle