| Magnetic anomaly detection is an important part of geophysical detection.Compared with other non-magnetic detection technologies,magnetic anomaly detection technology has strong concealment,identification and positioning capabilities,and is less restricted by the environment.Currently,it plays a great role in the fields of medical diagnosis,military target identification and positioning,underground resource exploration and so on.Magnetic detection technology based on magnetic gradient tensor uses magnetic gradient tensor as information source,which can obtain more abundant information.It is one of the most widely used magnetic detection technologies at present.Western scientific and technological powers started this research as early as the 1940 s,and have made some experimental results.However,China started late,and still stays at the theoretical level.this technology urgently needs to break through technical barriers,which is the key development direction supported by the state at present.Therefore,it is of great significance to develop the research on the magnetic gradient tensor localization technology.Firstly,this paper expounds the research status of magnetic detection and positioning method and tensor measurement system at home and abroad,then analyzes the mechanism of magnetic anomaly,makes an in-depth study on the frontier development direction in the field of magnetic detection,that is,magnetic gradient tensor detection,and introduces the basic theory of magnetic gradient tensor in magnetic gradient tensor detection technology.According to the configurations of five common tensor measurement systems,the principle of measuring gradient tensor under each configuration is deduced.The advantages and disadvantages of different configurations are analyzed.Because the cross configuration tensor measurement error is low and the structure is simple,finally,the cross configuration is selected to build the magnetic gradient tensor measurement system.Secondly,the spatial three-dimensional magnetic dipole model is established.On this basis,combined with the magnetic gradient tensor theory,the principles of three target positioning algorithms based on the magnetic gradient tensor information are described and deduced in detail,and the advantages and disadvantages of each algorithm are analyzed.Finally,aiming at the shortcomings of the three positioning algorithms,a target positioning algorithm based on the geometric invariants of the magnetic gradient tensor is proposed.Simulation results show that this method eliminates the influence of background geomagnetic field and interference magnetic field noise,is not limited by direction and angle,and the positioning accuracy is greatly improved.Then,the error correction of the magnetic gradient tensor measurement system is studied,the generation mechanism of the manufacturing error of a single sensor and the misalignment error of the measurement system are analyzed,and its error model is deduced.Finally,a method of error correction based on the linear relationship between multi-sensor orthogonal systems is proposed.The correction can be completed only by collecting four groups of attitude information.In the simulation analysis,the prediction accuracy of error angle is higher than99.7%,After the measurement and correction,the RMSE value of tensor component is reduced to less than 65 nt / m,which improves the detection accuracy of tensor measurement system.Finally,the correctness of the magnetic dipole model is verified by the design test,and the magnetic target positioning system is built for the field positioning test.The test results show that the positioning error of the magnetic target positioning system for small ferromagnets is less than 5% within 6m,and less than 10% within 6m?8m.It has a good positioning effect,and provides a feasible scheme for magnetic target detection and positioning. |
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