Research Of Key Technologies In Geomagnetic Navigation

As a new technology the geomagnetic navigation system has several obvious advantages. The most important one is that its effectiveness is not affected by external factors such as weather, location and topographical factors, thus it is an ideal complement to traditional navigation systems and has a broad research and application prospects. The branches of this technology include the following research fields: geomagnetic survey and mapping, disturbance separation, geomagnetic matching algorithms and filtering technologies. This thesis covers several important techniques in the branches above, and its research results are summarized as follows:The traditional aeromagnetic compensation method is improved and a new method for underwater geomagnetic mapping and correction is developed. Focusing on the movement coupling problems in the traditional aeromagnetic compensation method, the compensation model is rebuilt based on rotation matrices and angular velocities, which is much simpler than the old model and can work in all attitudes. Filtering method is applied to substitute equation solving method, which guarantees the new algorithm to have stronger anti-interference ability. Underwater vehicles can't float frequently to receive GPS signals, so mapping errors are often caused by their inertial navigation systems. Focusing on this problem, a new algorithm for GPS independent geomagnetic mapping method is developed. The algorithm is divided into three steps: Firstly, an inaccurate map is created with magnetic measurement data and position output from inertial navigation systems. Secondly, the map is analyzed and processed to extract shape information. Thirdly, another survey is conducted along the same route, and an extended Kalman filter is constructed with the shape information of the original map, the status of the inertial navigation system as well as the new measurement data, which helps to form a much more accurate map. The effectiveness of the new method is verified by both theoretical analysis and simulation results.The low-frequency electromagnetic interference is one of the major obstacles for geomagnetic navigation systems because it is hard to isolate, model or filter. A new method based on independent components analysis is developed to solve the problem. The features of magnetic field produced by different types of circuits are analyzed, and then the branches of a circuit are divided into several independent interference sources, the attitude of the carrier is also regulated. A linear superposition model of all magnetic compositions is built based on all efforts above, which guarantees the application prerequisites of ICA are fulfilled. A map matching method based on correlation coefficient is proposed to conquer the ambiguity drawbacks of ICA.Focusing on the deficiencies of traditional geomagnetic matching methods, two new algorithms are proposed. One is based on intersected contour lines of geomagnetic field and gravitational field, which doesn't need the trajectory shape constraint, thus has better real-time performance. The other one is based on linear fitting of multi-level sub maps. This algorithm builds up location estimation areas and utilizes sub maps to perform coarse to fine locating strategy that works efficiently in areas with smooth geomagnetic surfaces. The application conditions of this algorithm are also given.A series of improvements for the traditional integrated geomagnetic navigation system based on EKF are made. To solve the divergence problem caused by flat geomagnetic terrain shapes, vector decomposition is implemented to improve the system's local observability; To solve the performance degradation caused by big linearization errors, unscented transformation is utilized to replace linearization methods in areas with severe undulating geomagnetic terrains; An adaptive filtering method is carried out to detect and track the switches of disturbance variance, which helps to overcome the uncertainty of sensor noise in complex environment; The new map-matching algorithm 3proposed in this thesis is also used to improve the integrated navigation system's performance.