Research On Full-wave Recognition Method Of 3-D Anomalies Based On ATEM

As an important backbone of national economy construction,mineral resources are not only the necessary means of production,but are also the powerful chips within the nationalcompetition,especially in the current booming economy.Although the ownership of mineral resources in China is very large,its development status is still not optimistic.As the contradiction between supply and demand of metallic ore resources becomes increasingly prominent,great resource gap comes up to be an important factor restricting China's economic and social development in a long period.In the metal mineral,shallow minerals which are easy to be found and identified are on the decrease,while the new,deep and concealed mines surrounding the old mining areas become the main ore body.The difficulty of the metallic ore exploration increases sharply.The traditional prospecting technology already cannot satisfy the detection requirements,therefore,studying a new technology and a new method of metal exploration is needed urgently.And the time-domain airborne electromagnetic method used as an effective method in mineral resources exploration also requires further research and development.The waveform for practical work on airborne time-domain electromagnetic method is trapezoidal wave,but in previous researches,the excitation waveform mostly aims at the step wave.The research for the full-waveform electromagnetic response under the trapezoidal wave excitation is lacking.And it did not study full-waveform response in the field of 3-D abnormal body parameter identification applications systematically.Aiming at the deficiencies,we carry out the following work:1.Based on the method of three-dimensional finite difference method,using the form of uneven ground grid subdivision,we calculate the step wave magnetic field gradient of the three-dimensional abnormal bodies,and we expand the model library especially for high-resistance and high-conductivity three-dimensional abnormal bodies.2.We study the full-waveform convolution algorithm under arbitrary waveform excitation.We lengthen dB/dt through the power-exponent-fitting method,calculate B excitated by the step-wave using the method of discrete numerical integration and then get the full-waveform electromagnetic responses by applying convolution method.Changing the switch-off-time of the ramp step wave gradually,we compare the dB/dt to the step wave's and verify the correctness of the full-waveform convolution algorithm.3.Based on the calculation of full-waveform electromagnetic response under the trapezoidal wave excitation,we analyze the influence of the turn-off time,conductivity and depth of the abnormal body to the detection resolution on the active period(i.e.,the switch-off-time)and passive period(i.e.,the off-time).We found that,the shorter the turn-off time is,the resolution of the switch-off-time period has more advantages over the off-time period.Until the turn-off time is 0.05ms,resolution of the switch-off-time period is 245.1%higher than that of the off-time section.For high conductivity and high resistance models,the resolution of the active period is superior to the passive period,and the greater the conductivity of the abnormal body is,the resolution of the active period has more obvious advantages.To the model of the shallow abnormal body,the active period resolution has evident advantages.When the depth becomes greater,the active period advantages fade out gradually,and eventually its resolutions gets closer to the one of the passive period.4.We extract the attributes of electromagnetic response respectively on the switch-off-time and the off-time period,and establish the regression equation on the parameter of the conductivity and the depth via stepwise regression and principal component regression method.In order to improve the precision of the whole-model regression equation,we optimize the accuracy of the regression equation and the identification process.Demonstrate an available method for joint parameters recognizing.The test results show that the model precision and the verifying accuracy are about 18%,the theory test proves the full-waveform parameter identification method of abnormal body is feasible.5.To test the actual application effect of the full-waveform parameter identification method,the project team carry out abnormal ring test experiments with the airborne time-domain electromagnetic system both in the laboratory and big goose island in Changchun.The relative error of joint identification results of the indoor experiment is less than 20%,while the relative error of outdoor experiment in big goose island is less than 25%.The actual test results show that the full-waveform parameter identification method of the abnormal body is effective.In this paper,we do comprehensive research on the full-waveform electromagnetic response under the trapezoidal wave excitation and its application,and prove the correctness and operability of the theoretical system by experiments.It is significant that the paper provides a more complete theory and method instruction for the airborne time-domain electromagnetic method.