Study On Underground 3D Target Recognition And Imaging Technology By Steady Current Field

High-resolution, precision is the development trend of ground target recognition and imaging. Coal resource is the main kind of energy in our country. Geological hazard likes Water Inrush, Caving and surface subsidence which are caused by unknown gob bring hazards to the safety of mine production, the life and property of residents. Electrical and electromagnetic methods are widely used in the detection of gob. because the resistivity of water-filled gob and surrounding rocks are quite different. The 2D High Resolution Rsistivity method by steady current field which has been widely used in the detection of gobs can achieve good results. 3D detection and imaging method is presented in this article to improve the detection accuracy and deficiency of 2D-HRR in 3D space, through the finite element analysis of target's response characteristics by steady current field underground. The Maxwell functions of steady current field are presented. And we give detailed proof to the potential boundary value problems of uniqueness theorem under the three types of boundary conditions. The approach of the first type boundary condition and the block method used in large-scale linear equations are presented for the HRR model of isolated target in homogeneous half space. The applicable use of HRR technique in the detection of mined areas and other isolated targets are confirmed by the finite element simulation results of underground 3D target. While the relationship between abnormal response and the position of target under the pole-dipole device is identified. Based on these theories, 2D-HRR can be extended to 3D-HRR and the hemispherical can also be used in direct imaging. The effectiveness of direct imaging and electrode arrangement presented in this article are confirmed by the flume experiments. In 2D-HRR, the position and shape of the anomaly might not be located very precisely. General 3D HDR methods are not sensitive enough to underground isolated target. And general 3D imaging algorithms are complicated, time consuming and difficult to converge. All of these problems can be solved by the direct imaging technology presented in 3D-HRR. Heavy measurement work is brought into 3D survey, but it is necessary for higher resolution and more accuracy location of the target. By the improvement of automatic 3D-HDR instrument, measuring cables and electrode devices, this scheme would be available in practical field exploration.