地面瞬变电磁系统标定的理论研究

Calibration of ground transient electromagnetic system

建立了以标定环为目标体的地面TEM系统标定模型,计算并分析了影响标定环响应(TLR)准确获取的七种非期望响应.研究结果表明,一次场响应(TR)和大地响应(TER、TRER)影响最大,可以通过背景场剔除方法加以剔除.接收线圈与标定环之间的高次互感响应TRLR、大地与标定环之间互感响应TELR幅度均超过标定环响应一个数量级,严重影响标定环早期响应的准确获取.通过调整标定环的直径、标定环与接收线圈之间垂直距离、标定环时间常数,可以有效地抑制TRLR的影响;通过合理配置标定环时间常数并选择高阻大地进行标定,可以有效抑制TELR的影响.本文的研究对准确标定、评价以及优化地面TEM接收系统具有指导意义.

Models are established for ground transient electromagnetic （TEM） system calibration by using a conductivity loop. Seven undesired responses are calculated and analyzed which influence the conductivity loop response （TLR）. The result indicates that the primary response （TR） and earth responses （TER、TRER） which make the most influence on the conductivity loop response （TLR） can be removed as background responses. The amplitude of high-order mutual induction responses TRLR between the receiver and conductivity loop or TELR between the earth and conductivity loop is at least one order of magnitude higher than TLR response, which greatly affect the early response of conductivity loop. TRLR response can be inhibited by adjusting the diameter of loop, the distance between receiver coil and conductivity loop and the time consistent of the conductivity loop. TELR response can also be inhibited by optimizing the consistent of the loop and choosing high resistivity ground as calibration site. In this paper, the way to calibrate the TEM system precisely has been studied, which can be used to calibrate and evaluate the TEM system and can also be used to optimize system parameters.