| Aeromagnetic survey technology has been developed since the 1930 s,and has become the most widely used magnetic exploration method because of its advantages of high efficiency and being unrestricted by terrain.In recent years,with the development of unmanned aerial vehicle’s(UAV)technology.The characteristics of rotorcraft UAV,such as safety,strong adaptability to terrain and small magnetic interference,provide a more flexible platform for fine detection in small survey areas.It has advantages and important significance in magnetic surveying tasks such as detecting unexploded explosives(UXO),locating solid wastes and delineating the boundary of coal seam fire zone.Magnetic gradient tensor describes the spatial change rate of magnetic field components.Compared with the total magnetic field and magnetic field components,it contains more information and has the ability to resist the time-varying interference of geomagnetic field,so it has become a hot spot in magnetic survey research.As a method to measure magnetic gradient tensor from the frequency domain,the rotation modulation method has lower hardware cost and only contains noise in single frequency point,which has more advantageous than other tensor measurement methods such as difference method and linear method.The research content of this paper is divided into two parts.The first part is the study of three-axis synchronous rotation gradiometer.Firstly,the principle of three-axis synchronous rotation modulation measurement is deduced,and the error source and transmission relationship of the three-axis synchronous rotation tensor instrument are analyzed according to the signal transmission path.The influence of static errors in mechanical,electronic,data processing and other aspects on the measurement results of the tensor is simulated and analyzed,which provides guidance for the design of the magnetic tensor gradiometer.Secondly,according to the simulation results,the static performance,dynamic performance and practicability of the instrument are considered,and the design scheme is studied.In terms of hardware design,it introduces the fixed design of probe part and the rotation design of the whole machine,the analysis of power supply and the design of signal conditioning circuit.In terms of software design,it introduces the design of upper computer acquisition software and embedded software,and gives the detailed process of tensor calculation.Finally,the accuracy of the measurement results is verified by magnetic dipole motion experiment.The resolution of the tensors is 5.27 n T/m under the condition of shielded cylinder.The second part is the research of mounting method of instrument and rotorcraft flight platform.Firstly,the UAV-pod joint motion model was established for the soft support measurement system,and the motion characteristics of the measurement pod under the multiple influences of its own gravity,aerodynamic factors and UAV tension were analyzed.Magnetic interference model and compensation method were studied for the hard support measurement system.Secondly,the dynamic error of the three-axis synchronous rotary tensors is simulated and analyzed.Finally,the field detection experiment was carried out,and the same target was detected by two mount modes respectively.The result shows that the static error of the instrument is amplified by the connection of the soft bracket,and the dynamic error of the instrument is increased by the coupling of the geomagnetic field caused by the movement of the pod.The threeaxis synchronous rotation gradiometer is more suitable to be mounted on the rotorcraft through the hard support connection.After magnetic interference compensation,the hard support measurement system has the ability to detect a small range of measurement area. |
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