| Scalar measurement can not obtain comprehensive magnetic field information because geomagnetic field is vector. Geomagnetic field vector measurement can overcome the disadvantage of scalar measurement. It is significant for geomagnetic navigation, magnetic object detection, earth structure analysis, mine detection and digital earth field modeling. Geomagnetic field vector measurement theory, error analysis of portable geomagnetic field vector measurement instrument, three axis magnetometer calibration, misalignment calibration and vector component of inertial system are researched. The measurement accuracy of the proposed instrument is evaluated, and it is used for magnetic abnormity mapping. The main research is introduced as follows:1. Portable geomagnetic field vector measurement instrument is designed, and the error reasons and influence are analyzed. The portable geomagnetic field vector measurement instrument includes of three axis magnetometer and inertial system. The influence of magnetometer error, misalignment and inertial system distortion field is analyzed. Error reasons are revealed. A comprehensive error model is established and error control is designed, which provides theory guidelines for optimal design and calibration/ compensation of geomagnetic field vector measurement instrument.2. Optimal research of key factors for three axis magnetometer calibration is implemented. L-M algorithm is proposed for magnetometer calibration. Compared with UKF, RLS, DE, Gauss-Newton and GA, L-M algorithm shows comprehensive advantages: sensitivity of initial parameters, calibration performance, robust and calculation time. Symmetrical calibration strategy is proposed, and the generality of calibration parameters is enhanced. Nonlinearity parameter of scale factor is considered, and integrated nonlinearity calibration model is proposed. After calibration, error is further reduced to 1/3 of traditional model. LSSVM temperature compensation method is proposed to overcome the problem that it is difficult to test scale factor and bias temperature characteristic. Then, temperature error is reduced by two orders.3. It is hard to guarantee that inertia system coordinate is the same with magnetometer coordinate; thus, two misalignment calibration methods using the changeless projection of magnetic field/gravity are proposed. A misalignment calibration method using changeless projection of magnetic field/gravity on fixed coordinate is proposed, in which an interim coordinate is established. The misalignment angles between interim coordinate and magnetometer/ inertia system coordinate are calculated respectively, and then, the misalignment angles between magnetometer coordinate and inertia system coordinate are obtained indirectly. In addition, a misalignment calibration method using changeless projection of magnetic field/gravity on vertical direction of plane is proposed to calibrate misalignment error. Different equipments and projection information are used in the two misalignment calibration methods. The two methods are effective for misalignment calibration which is hard to be solved by mechanical methods.4. In order to overcome the problem that scalar compensation method is not effective for component compensation, component compensation methods are proposed. The component compensation performance of scalar component method is researched in theory and experiment. A component compensation method using right angle platform is proposed. Using the designed assistant equipments, true values of magnetic field components are used for component restriction for compensation. A component compensation method using relative change of attitude for component restriction is proposed, in which true values at each attitude are not required. A component compensation method using geomagnetic field information is proposed, in which true values of component are not required, and it is not necessary to solve high dimensions of nonlinear equations. All of the three component components methods are effective for component compensation, and the appropriate method should be chose depending on application situation.5. The portable geomagnetic field measurement instrument is tested in experiment, and it is used for magnetic abnormity mapping, and then, perforamce test and evaluation methods are established. Three dimension static test and small range dynamic test are implemented. After calibration and compensation, north, vertical and east direction geomagnetic field error are reduced to 2.09 %, 2.0 % and 3.4 %. The proposed system is used for local magnetic abnormity mapping to demonstrate that it can overcome the disadvantage of scalar measurement methods. |
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