| The vehicles sailing in the ocean environment mainly use the Inertial Navigation System(INS) for navigation, especially the vehicle of underwater. INS has the following characteristics that the short-term accuracy is so higher, but the error will accumulate over time. So the vehicle need regular surface the water to correct the error using the satellite positioning or other methods.However, the process can reduce its safety and concealment. In recent years, geomagnetic navigation method become one of the important aided navigation method for INS. But the precondition of realizing geomagnetic aided navigation is to measure the geomagnetic field.The measurement in the ocean environment almost depends on the ship, underwater robots and other underwater vehicle, and these vehicles are mostly made of ferromagnetic material. When the ferromagnetic material is magnetized by the geomagnetic field, it can produce some additional magnetic field around the vehicle and the complex magnetic field will influence the measurement of the geomagnetic field. This paper is supported by the national "twelfth five-year" plan, which mainly researches the separation method between the complex interference magnetic field and the geomagnetic field, based on the traditional detection method to establish the new vector difference measurement model and the vector difference calculate model. Two kinds of geomagnetic detection methods are proposed and the process of calculating the related parameters are researched. Through the simulation and experiment verify the feasibility of the two detection methods.The research of the paper provides important basis for the measurement of the geomagnetic field vector datas in the ocean environment. The main research contents and achievements of this paper are as follows:(1)The spatial distribution characteristics of the main magnetic field around the ferromagnetic vehicle were studied. Firstly, the elements and spatial distribution characteristics of the geomagnetic field were analyzed and the spherical cap harmonic model theory calculation method and the basic principle of the geomagnetic field were illustrated.Then the magnetic field type and mechanism around the vehicle were studied, mainly including the induced magnetic field and the permanent magnetic field. The mathematic law between the induced magnetic field and geomagnetic field were summarized and the amplitude attenuation curve of the induced magnetic field changing with distance was studied.Finally,the magnetic characteristics of other magnetic field interference source, such as the shore magnetic source, eddy current magnetic field and surface ships had been carried out detailed researched and simulated.(2)The theory of geomagnetic field vector difference detection method on the ferromagnetic vehicle was researched. The detection principle and the measurement process of the traditional shipborne three-component measurement(STCM) system were analyzed,and the shortages based on the STCM measurement model were introduced.We proposed two geomagnetic field detection methods which are the time difference measurement method(TDD) and the spatial difference measurement method(SDD), and introduced the calculating method of the induced magnetic field relation matrix, the induced magnetic field differential coefficient matrix and permanent magnetic field.The difference calculating method of the related parameters can get a better estimation results, which reduces the demand for the background uniform magnetic field environment.We analyzed the sensor calibration method and the error which may caused in the TDD and SDD method. The spatial layout optimization design of the sensors in SDD method was researched, and we proved the spatial displacement installation method that can get better results.Finally, the applicable condition and ideal application environment of the both difference detection method was analyzed.(3)Ferromagnetic vehicle magnetic vector detection method was simulated by the computer on the strong interference environment.According to the spatial distribution characteristics of geomagnetic field and detection requirements,the geomagnetic field vector detection simulation system was developed combined the finite element simulation software and Matlab.The spatial distribution rule of different size vehicle and magnetic field isosurface were researched.The optimum proposal was put forward about different size vehicle sensor layout.The STCM TDD and SDD were compared research.Geomagnetic field vector testing simulation system used the relative coordinates rotating technology between the vehicle and the geomagnetic field to solve the problem of the magnetic survey data can't been read because of the inconsistent between the vehicle coordinate system and the geographic coordinates system.The simulation system was convenient to complete the basic modeling, subdivision of ferromagnetic vehiche, magnetic field calculation and data saving through internal data flow control, and the realization of dot, line, surface mapping and analysis of simulation data. Finally it will realize data processing depending on different detection algorithm and graphic display of the simulation results.(4)Ferromagnetic vehicle geomagnetic field vector difference detection method was tested by the experiment research.Any one new detection method need experiment to find problems and gradually improved.Because there are not parallel multi-channel magnetic vector and simultaneously provide multiplex acquisition of data acquisition system can be used, this paper developed a set of geomagnetic field vector testing experiment system, based on FPGA as control core and sensors using the Bartiongton-Mag03 three-component flux-gate whose measurement accuracy is 0.1 n T and the PC using Lab View as human-computer interaction interface. The space layout and not orthogonal of the vector sensor were studied and the experimental vehicle model and the experiment platform were design to form a complete testing system.This paper designed the indoor shielding experiment, outdoor ground experiment and water surface experiment. In order to remove the high frequency noise and detect complex collinearity equations appear, experimental data preprocessing method is proposed, At the same time,a software of magnetic vector difference detection method based on Matlab-GUI was developed,which was used to process the experiment data and realize the verification and evaluation of geomagnetic field test results. |
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