Magnetic perturbations detection and heading estimation using magnetometers

With the advent of smart phones equipped with Micro-Electro-Mechanical Systems, it has become possible to utilise one's orientation information along with location for Location-Based Services applications. Although gyroscopes are considered to be the primary sensors for orientation estimation, associated errors require periodic updates from other sources to mitigate them. Accelerometers can be used for estimating roll and pitch angles and magnetometers for estimating heading. However, the presence of man-made magnetic anomalies caused by electronic devices, ferrous materials, mechanical and electrical infrastructures contaminates the measurements since only the Earth's magnetic field is useful for estimating magnetically derived heading. Without proper magnetic disturbances detection and mitigation technique, heading estimates become erroneous and can corrupt the entire location estimation process. Because heading is the primary source of error in pedestrian navigation and the magnetic field is available everywhere, an exhaustive analysis of magnetic anomalies and their impact on heading estimation has been conducted using data collected in six different pedestrian environments. Based on the statistical outcomes, a magnitude-and angle-based detector of magnetic disturbances has been developed. This information is also used for estimating the accuracy of the magnetically derived heading, which can further assist sensor fusion algorithms. An experimental assessment of the proposed detector was conducted in a shopping mall. A theoretical analysis and experimental results show that the proposed detector is capable of identifying the effects of perturbations on the Earth's magnetic field, which provides users with a better estimate of magnetic heading in different pedestrian navigation environments.