Localization Of Magnetic Target Using The Array With Total Field Magnetometers

The magnetic anomaly is caused by magnetic target,which can generate the magnetic field and change the geomagnetic field distribution of its surrounding space.The position and magnetic moment of the target can be estimated through the technologies based on the measurement and inversion of magnetic anomaly.Recently,along with the development of the magnetic field detection and navigation of vehicles,the localization of magnetic target based on mobile platform has been applied in many areas,such as unexploded ordnance,submarine pipeline and underwater target,etc.Due to not being affected by the vibration of mobile platform,scalar magnetometer array has an important academic research significance and engineering application for tracking and locating the magnetic target.The thesis focused on the issues of target localization based on scalar magnetometer array.The main research of the thesis was as follows:An algorithm and modified algorithm based on scalar magnetometer array for locating the magnetic target were proposed.Comparing with vector magnetometers,the scalar magnetometer is insensitivity to the rotational vibrations.Therefore,it is an important advantage for measuring the magnetic anomaly on the moving platform.In the thesis,the feasibility of locating the target based on the scalar magnetometers was analyzed and the measurement model of the scalar magnetometer in the localization was built.Then,the measurement error of the model was analyzed in detail.An array with the scalar magnetometers was presented,which can be used to locate the magnetic target.A method for locating the target was proposed.In the method,an optimization problem for estimating the parameters of the target was built,which was based on the position relationship of the magnetometer in the array.Three algorithms(Levenberg-Marquardt algorithm,Genetic Algorithms,Particle Swarm Optimization algorithm)for solving this optimization problem were compared and analyzed.The results were shown that the PSO algorithm was fit for solving this problem.In order to improve the positioning accuracy and computing efficiency,a modified algorithm based on magnetic moment was proposed for locating the target.Meanwhile,a dedicated PSO algorithm was developed for solving the optimization problem.In the simulation,results were shown that the modified algorithm can improve the positioning accuracy in the condition of low signal-to-noise ratio(SNR).The experiment was carried out and the results verified the effectiveness of the proposed methods.A fast linear algorithm base on total magnetic gradients for magnetic target localization was proposed.Due to the iterative process in the optimal algorithms,they are not suitable for fast real-time locating the magnetic targets.The magnetic moment of the target was analyzed in detail.And the fast linear algorithm was proposed for locating the static target with soft magnetic moment.In the algorithm,a cubic equation of any parameter of target position was derived according to the property of the dot product and the cross product.Then,a closed-form formula of the target position was obtained.Therefore,the position and moment of the target can be directly calculated according to the closed-form formula.The proposed algorithm was validated by the simulation and real experiment data.The results were shown that the execution time of the proposed algorithm was far less than that of PSO algorithm.Therefore,the proposed algorithm can be used to locate the target in real-time.An algorithm based on total magnetic gradients for tracking a moving magnetic target was proposed.Firstly,a model of moving target was built,which was equivalent to a first-order Markov process.According to this model,an optimization problem was obtained through the matrix transformation.The parameters of moving target are estimated by solving the optimization.By using the proposed method,we can estimate not only the target's position and the magnitude of the magnetic moment,but also the velocity of the moving target.The proposed algorithm was validated by the simulation and real experiment data.A method for the baseline optimization of the array was proposed.The magnetic anomaly measurement based on the array was analyzed.A measurement model of magnetic gradient was built.According to this model,the formula of SNR was derived,which was an evaluation criterion for baseline optimization in Monte Carlo simulation.The optimal baseline can be obtained using the proposed method according the detection requirements.In the simulation and experiment,the target was located using the array with different baselines.The results were shown that the accuracy of localization was better with the optimal baseline.