Research On Geomagnetic Tensor Measurement Technology Based On Fluxgate Magnetometer

As one of the earliest and most important geophysical measurement methods,magnetic measurement has a wide range of applications in geophysical research,military engineering and other fields.With the continuous development of science and technology,magnetic measurement has developed from measurement of the total strength of geomagnetic field and three-component measurement of geomagnetic field to measurement of magnetic field gradient tensor.Foreign countries have started research and development of full tensor magnetic gradient meters very early.The United States,Germany,Australia and some European countries have developed their own full tensor magnetic gradient meters,and have achieved some experimental results.China is still in its infancy in the measurement of full tensor magnetic gradient,so the development of full tensor magnetic gradient instrument has important significance.In this paper,the measurement error of magnetic gradient tensor in different configurations is analyzed.The error model of magnetic gradient tensor is established.The measurement error correction method of magnetic gradient tensor is proposed.The feasibility of the method is verified by calibration experiments.A magnetic field gradient tensor measuring instrument based on a fluxgate magnetometer was designed and developed.This paper briefly introduces the basic properties of magnetic field gradient tensor and the research status of magnetic field gradient tensor measurement at home and abroad,and illustrates the advantages of magnetic field gradient tensor measurement.The structure and circuit design of the three-axis fluxgate magnetometer are briefly described.Five basic magnetic gradient tensor configurations of triangle,cross,rightangled tetrahedron,regular tetrahedron and square are introduced.By simulating the error of five basic magnetic gradient tensor configurations,the simulation results of each configuration are compared.The conclusion that the cross-shaped configuration magnetic gradient tensor has the smallest measurement error determines that the geometry of the developed magnetic field gradient tensor is a cross-shaped configuration.Based on the above analysis,this paper analyzes the error model of the fluxgate gradient tensor,and the error of the gradient tensor is mainly divided into two parts.The error of the four fluxgate magnetometers composing the gradient tensor,mainly three-axis non-positive,Intersection error,inter-axis scale factor error,triaxial zero offset error,etc.And misalignment errors due to mechanical precision or human operation when installing a gradient tensor.In this paper,a non-aligned error correction algorithm is proposed.The algorithm is simulated and experimentally verified.The error between the corrected magnetic field gradient tensor and the magnetic field gradient tensor before correction are reduced by 83.7%.The proposed calibration method can well correct the error of the magnetic gradient tensor.After verifying the correction algorithm of the magnetic field gradient tensor,this paper developed a magnetic field gradient tensor based on the existing fluxgate sensor in the laboratory.The signal detection circuit part of the magnetic field gradient tensor is designed and completed.After the circuit debugging is completed,the performance test of the fluxgate sensor and circuit is carried out,which achieves a good performance standard.