Research On Aeromagnetic Three-component Detection System

Aeromagnetic survey is an important way of resource investigation and prospecting targets screening.The magnetic measuring instruments equipped on aircraft can measure slight magnetic changes which caused by the magnetic mineral resources.In order to assess the magnetic mineral resource types and distribution, information processing technology is used to achieve the spatial distribution of underground ore body imaging. With the continuous development of magnetic exploration theories and methods, for the purpose of improving the detecting resolution and positioning accuracy of underground ore bodies, more geomagnetic information is necessary. This promote the major aeromagnetic technology from total field strength measurement to total field gradient measurements, and then to the vector (three components) measurement and full tensor multi-parameter measurement. However,the major instrument for aeromagnetic survey are still optical-pumping magnetometer, proton precession magnetometer and overhauser magnetometer,which are to measure the scalar parameters of total magnetic field or total magnetic field gradient. Compared with the existing magnetic survey methods,vector magnetic survey is able to obtain modulus size and orientation information of he magnetic field simultaneously, which will effectively reduce the multiple solutions of inversion.Vector magnetic survey is helpful to the qualitative and quantitative interpretation of the magnetic body, improving underground ore body detection resolution and positioning accuracy.Because of these advantages,vector magnetic survey has attracted more and more attention by geophysicists. This research is funded by the Sub-topic(aeromagnetic vector(three-component) measurements key technology research and prototype development) of national 863 project-"Airborne geophysical exploration technology systems".The main contents and results are as follows:(1) The development of aero three-component fluxgate magnetometer is completed. The relevant tests and experiments of performance parameters(accuracy, linearity, orthogonality,noise level,etc) is conducted. Test results show that three-component fluxgate magnetometer measurement range is 7.5 X 104nT, nonlinear relative error is less than 0.008% FS, the noise level is below 1Hz 0.1nt/√Hz at 1Hz, dynamic range is greater than 132db, orthogonal angle error is less than 0.004 °. The noise shield is used in the three-component fluxgate magnetometer data acquisition device.Serial communication software for the PC 104 is programed. After testing,the software can be guaranteed to work properly in a high rate, strong interference environment.(2) The drive circuit and analog processing circuit of fluxgate probe is designed base on the second harmonic. The development and calibration of three-component fluxgate magnetometer is completed. Analog processing circuitry is constitute by preamplifier, band-pass filter, phase-sensitive detector, low-pass filter, integrator and feedback loops. Digitizing module is consisted of 24 AD acquisition, flash memory, FAT32 file system-based on storage SD card, the clock module, interactive modules and communication modules. In the software design, a lower computer program is established based on C/C++ class framework. It achieved the data acquisition, storage, digital filtering, transmission and user interface. PC USB receiver software is based on C #.(3) Several key technical is used in the equipment development process, including the lock-in amplifier technology, triaxial not orthogonal degree correction method, apparatus, closed-loop analysis and dynamic response compensation. Lock-in amplifier technology, introduces the basic principles of lock-in amplifier and associated detection circuit after expounded the necessity of switching phase sensitive detector flux gate analog processing. Triaxial not orthogonal degree correction method in the analysis of the impact of the three components of the non-orthogonal magnetic field measurements made to bring non-orthogonal triaxial measurement and correction of the way, the real test of the three components of the probe showed that the method measurement and correction of non-orthogonal angle error can be reduced to 0.004 °. Instrument closed-loop dynamic response analysis and compensation, based on Matlab/Simulink to establish a flux gate analog processing circuit negative feedback loop system simulation model, the impact of the main research feedback loop dynamic response of the instrument parameters, finally adopted a step ahead of the system of compensation response is improved.(4) Magnetometer data collection is based on the carrier’s own coordinate system, the data along with the transformed coordinate system and random variation, inertial navigation device records the attitude information (roll angle, pitch angle and azimuth) are based on the geographic coordinate system the attitude information is always at a fixed reference coordinate system for measurement. By the coordinate transformation between the two coordinate systems, based on the data changing carrier coordinate system to transform the magnetic field data (reference coordinate system) based on geographic coordinate system under, in order to achieve an imaging coordinate system of the magnetic field in the same data, to facilitate Interpretation and analysis of aviation magnetic field measurement.(5) The inertial navigation system main parameters positioning accuracy, the attitude angle accuracy, speed, accuracy, and drift tests and experiments related to the work principle and the use of the inertial navigation system was related research, for each navigation system working states depth analysis to study the GNSS/inertial navigation system’s network interface communication protocol, and its network communication protocol written relevant data receiving software.(6) Completed the assembly and commissioning of the entire system, and for the testing of the entire system in Changchun suburb pot roast town designed field magnetic anomalies designated testing laboratory, through data analysis results correctly reflect the magnetic anomaly for GNSS/inertial navigation system posture correction effect of three-component fluxgate magnetometer in field experiments conducted field trials to test the attitude transformation, data analysis results also played a significant effect.This innovation as follows:(1) A three-component detection system aeromagnetic is developed. By analyzing the three-component magnetic aeromagnetic survey works, the use of three-component developed aeromagnetic fluxgate magnetometer and precision INS/GPS inertial navigation system aeromagnetic study of three-component measurement method for three-component magnetic data synchronization between the data and the attitude, design the corresponding data acquisition and synchronization technology, eventually developed, including three-component magnetic probes, GPS, inertial navigation systems, data acquisition systems, the primary measurement and control system and the PC processing software aeromagnetic three components of the detection system.(2) A three orthogonal components of the magnetic probe measurement and calibration methods is proposed. Because of the level of technology, production and installation errors exist, the actual three-component magnetic probe can not be absolutely ideal quadrature, which will bring three-component measurement error. This paper presents a relatively stable environment in the field of space, the use of non-magnetic rotating platform measuring method of the orthogonal sensors. And the establishment of the coordinate system, the sensor forward and inverse orthogonal degree, a mathematical model to obtain orthogonal correction parameters, and use the total market value of the correction effect for verification, and achieved good results, for the next three-component measured by the and posture correction work of the foundation.(3) A three-component aeromagnetic posture correction method. Through the three-component magnetic measurement system coordinate system to analyze the relationship between mathematical logic and geographic coordinate measuring coordinates using coordinate rotation algorithm to get the coordinate transformation matrix. And using the experimental system developed posture correction posture correction in the field experiments carried out to verify the magnetic measurement system posture correction algorithm performance and results, for carrying out the actual flight magnetic three-component magnetic measurement system to lay the technical and theoretical basis.Through this study, the development of a three-component detection system aeromagnetic solve the three-component fluxgate sensor orthogonal degree of influence on the actual measurement error problem, studied and implemented a three-component magnetic measurement system posture correction algorithm. Through in-house testing, calibration and field experiments to verify the actual performance of magnetic measurement system provides important technical reserves for China to carry out the actual flight measurements aeromagnetic three-component magnetic measurement system in the future, in solid mineral exploration, oil and gas exploration, defense and other areas has broad application prospects.