| Aeromagnetic survey,also known as aeromagnetic detection,is the earliest and most widely used magnetic survey method in the field of aerogeophysical exploration.Loading magnetic sensors and their supporting auxiliary equipment on aircrafts and detecting magnetic anomalies generated by magnetic differences of underground ore bodies,aeromagnetic survey can achieve rapid survey of oil,natural gas and other mineral resources,which plays important roles in resource exploration and geoscience research.With the development of magnetic exploration theory and the improvement of magnetic survey equipment performance,aeromagnetic survey has undergone stages from traditional single survey of total field to later gradient survey of total field and the currently magnetic vector survey.Its overall development trend has changed from single scalar magnetic survey object to multi-information vector field or multi-parameter survey,among which three-component magnetic survey is one of the major development directions in aeromagnetic survey at present.Compared with aeromagnetic total field survey and aeromagnetic total field gradient survey,aeromagnetic three-component magnetic survey covers all elements of magnetic anomalies including sizes and directions,which effectively reduces multiple solutions in inversion and has obvious advantages in magnetic anomaly interpretation.Actually,magnetic survey of high quality is the foundation for the application of aeromagnetic three-component magnetic survey.However,factors like errors from magnetic survey system and magnetic interference will inevitably affect the magnetic survey accuracy,thus making it quite challenging to guarantee high quality magnetic survey.Therefore,it is in urgent need to explore effective methods to eliminate errors in magnetic survey so as to ensure the accuracy of aeromagnetic three-component magnetic survey.This thesis makes a comprehensive review of the error sources in aeromagnetic three-component magnetic survey and conducts further research to explore feasible as well as effective methods for magnetic survey system error calibration and magnetic interference compensation.The main content and results of the present research are as follows:(1)A comprehensive analysis of error sources in aeromagnetic three-component magnetic survey is presented,after which the procedure of magnetic survey system error calibration and interference compensation is introduced in details.According to different error sources,error sources in aeromagnetic three-component magnetic survey are mainly divided into magnetic survey system errors and external magnetic interference.Magnetic survey system errors are manifested as errors from tri-axial magnetic sensor and misalignment errors of magnetic survey system.External magnetic interference originates from the interference magnetic field generated by UAV body as well as the magnetic diurnal variation interference.On the basis of internal correlation between the above-mentioned error factors in magnetic survey,the thesis proposes the procedure of magnetic survey system error calibration and interference compensation,that is,first to calibrate errors from the tri-axial magnetic sensor,then to calibrate the misalignment errors in the magnetic survey system,next to compensate interference magnetic field generated by UAV body,and finally to compensate the magnetic diurnal variation interference.(2)A novel method of tri-axial magnetic sensor errors calibration is proposed in the thesis.Prior to the aeromagnetic three-component magnetic survey,it is required to calibrate tri-axis magnetic sensor errors.However,due to the limitation of field experimental conditions,tri-axial magnetic sensor errors can hardly be calibrated using auxiliary equipment such as Helmholtz coils.Therefore,it is quite necessary to research an effective method for tri-axial magnetic sensor errors calibration in the field environment,especially in the absence of precise auxiliary equipment.In this thesis,mechanism of tri-axial magnetic sensor errors is analyzed firstly,based on which a comprehensive calibration model of tri-axial magnetic sensor errors is constructed according to the specific manifestations of different errors.Then,the scalar calibration method based on the ellipsoid hypothesis is studied.To solve the problem of sensitivity to magnetic survey noise during magnetic survey trajectory fitting,a noise suppression scheme is proposed for magnetic survey which combines robust fitting with scalar calibration method.Finally,the simulation experiment and field experiment is carried out,results of which show that the proposed scheme can not only make spot calibration of tri-axial magnetic sensor errors in the field environment,but also effectively suppress the magnetic survey noise,thus ensuring the calibration accuracy of tri-axial magnetic sensor errors.(3)A novel calibration method of misalignment errors in the magnetic survey system is proposed in the thesis.Due to the invisibility of the three axes of magnetic sensor and inertial navigation system when assembling the strapdown three-component magnetic survey system,the magnetic survey accuracy is affected seriously by misalignment errors generated from the axial misalignment.In this thesis,an in-depth analysis of misalignment errors of magnetic survey system is presented explicitly at first,base on which,a misalignment error calibration model is constructed by introducing a rotation matrix according to the spatial rotation principles of three-dimensional coordinate system.Subsequently,a plane rotation calibration method is proposed based on the invariance of normal vector of plane rotation,after which the simulation experiment and field experiment is carried out.The simulation results show that the present method achieves excellent calibration effect under different noise levels.The field experiment results show that the calibration accuracy of the method is better than that of DPI method.Meanwhile,with the obvious advantage in operability,the proposed method overcomes the disadvantage of DPI method being sensitive to auxiliary vectors.(4)A novel compensation method of the UAV body magnetic interference is proposed in the thesis.Originated from the magnetized ferromagnetic materials in the UAV's airframe by the geomagnetic field,the interference magnetic field is inevitably superimposed on magnetic survey results of each component during the operation of magnetic survey,thus reducing the magnetic survey accuracy to a large extent.In this thesis,an intensive study on characteristics and spatial distribution of the interference magnetic field is conducted primarily,based on which,several physical strategies are presented to reduce the magnetic interference of the airframe during the integration of UAV and magnetic survey system.Then,a comprehensive compensation model for magnetic interference is constructed aiming at the main components of the interference magnetic field,namely the induced magnetic field and the fixed magnetic field.Subsequently,a parameter estimation compensation method based on CS algorithm is proposed according to the component constraint principles.Finally,the simulation experiment and field flight experiment are carried out,results of which show that the proposed method has higher compensation accuracy than that of the methods based on UKF and GA and it also overcomes the shortcomings that UKF method is sensitive to iterative initial value and GA method is easily to get stuck at local optimal value.In addition,the proposed method has strong global optimization search capability and good robustness,thus ensuring convergence to the optimal solution when solving the iterative operation of magnetic compensation parameters.(5)A novel compensation method of three-component magnetic diurnal variation interference is proposed in the thesis.Influenced by periodic activities of the sun,the intensity and direction of geomagnetic field show a periodic variation,taking a cycle of 24 hours with daily-varied amplitude,which is called geomagnetic diurnal variation(hereinafter also called magnetic diurnal variation).For high precision aeromagnetic three-component magnetic survey,magnetic diurnal variation is an influencing factor that cannot be ignored in the process of magnetic survey.This thesis proposes a mobile ground observation method for three-component magnetic diurnal variation,which can effectively observe the three-component magnetic diurnal variation information in spatial geographic coordinate system so as to make effective compensation of it.Results of the field experiment show that observation accuracy of the proposed method can meet requirements of high-precision compensation of three-component magnetic diurnal variation.In addition,with the advantage of simple operation and portability of equipment used,the proposed method makes it possible to set up diurnal variation observation station in areas with complex topography to assist aeromagnetic three-component magnetic survey. |
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