Investigation of Magnetic Compass Accuracy at Ground Level

In this thesis the possible heading accuracy of a magnetic compass and the distortions to the earth’s magnetic field present in different environments at ground level is investigated. A three axial magnetometer is used to measure the magnetic field and derive the heading. Magnetometer readings are corrected for distortions generated by the measurement equipment and the derived heading is compared to that of an inertial navigation system. The magnetometer is maintained near horizontal at all times meaning that the z-component of the field has very little impact on the heading. The magnetic field is investigated in three different situations: Along a countryside road with no man made distortions present, around buildings in an urban environment and around a typical car. Results from measuring along the countryside road indicate that this environment may be suited for magnetic compassing as the heading error remained within 1 degree. In the urban environment, the level of distortion was high. Heading error could in the measurement here be kept to within 5 degrees when measuring in the middle of roads in between buildings but the error quickly increased when approaching buildings. When larger open areas are present and the distance to buildings was over 10 m, the error reduced to within 2 degrees for some locations. These results suggest that heading in an urban environment may be very unreliable. The distortion caused by the car may influence heading by 1 degree out to a distance of 6-7 m depending on its orientation relative to the earth’s field. The cars field appears to be mainly generated by the car itself independently of the earth’s field.Validerat; 20110607 (anonymous