Research On Detection Accuracy Of Unexploded Ordnance In Portable Transient Electromagnetic System

Unexploded ordnance detection using transient electromagnetic method,the accurate positioning and characterization of the target is the key to unexploded ordnance detection,usually the unexploded ordnance is equivalent to a point dipole to facilitate the positioning and characterization of the target.However,in practice,because the target has a certain volume and is close to the sensor,the distance between different parts of the target and the sensor varies,which will lead to detection errors.In this thesis,based on the differential evolutionary algorithm,we investigate the influence of target size,burial depth and inclination angle on target detection accuracy based on the measured unexploded ordnance response of the portable system.First,this thesis introduces the mainstream detection technology of unexploded ordnance,and at the same time introduces three mature transient electromagnetic detection systems airborne,vehicle-mounted and portable transient electromagnetic systems.On this basis,the basic theory and detection principle of the transient electromagnetic method are explored,and the system structure,detection method and data processing of the portable transient electromagnetic detection system used in the experiment are briefly introduced.Next,the dipole model theory is described in detail in this thesis.Including the derivation of the field and the calculation of the characteristic response,the basic theory of the differential evolution algorithm is introduced,and the basic flow chart of the algorithm is given and the specific implementation steps are analyzed.The forward simulation is carried out according to the system parameters,the measured line response and plane response of the portable system are discussed,and the inversion of the position and feature response of the differential evolution algorithm is carried out with an 82 mm mortar shell as an example,and the inversion process is analyzed.Finally,several factors affecting the accuracy of target localization and characterization,target depth,inclination angle and size,are experimentally designed to investigate the influence law of the above factors on the accuracy of target localization and characterization.Subsequently,the inversion of the target angle was carried out,and the error prediction of the target localization results could be made based on the angle inversion results,and finally further validated by the single-target experiment and the double-target experiment in the field experiment.The experimental results show that the feature response and dipole equivalent position of the small inclination target are more concentrated in the head of the target,and the localization and feature response results are smaller than the calibration value,while the feature response of the large inclination target is the superposition of the feature response of all parts of the target,and the localization and feature response results are larger than the calibration value;the greater the depth,the higher the applicability of the dipole model,and the better the consistency of the feature response under different inclination angles,when the equivalent The greater the depth,the higher the applicability of the dipole model,the better the consistency of the characteristic response under different inclination angles,the more the equivalent dipole model is affected by the change of inclination angle,the dipole model can only respond to some of the characteristics of the target,and the positioning error is larger,while the consistency of the characteristic response of each angle of the small-sized target is better,and the angle change has relatively less impact on the results.