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时间域航空电磁系统的探测深度是一项关键技术参数,在系统研制设计和资料解释中都有重要作用.当目标层与围岩电性差异不大或目标层引起的异常响应不明显时,常规的估算探测深度方法不再适用,为克服这种缺陷,本文提出了一种系统探测深度的估算方法,该方法通过模拟电场在均匀半空间模型和层状模型中的扩散过程,记录电场最大幅值在地下的瞬时位置,将系统的探测深度定义为观测到的响应值等于给定的噪声水平时,对应时刻的地下介质中感应电场幅度的最大值对应的深度.论文以我国自主研制的直升机时间域航空电磁系统CHTEM-I为例,根据对不同条件下的计算结果的分析,给出了探测深度与模型电导率、飞行高度和噪声水平之间的关系曲线,并总结出一些能够提高系统探测深度的建议.结果表明半空间模型电导率在0.000295~0.0422S/m范围内,CHTEM-I系统可以在噪声水平与t-0.5成正比条件下达到300m的探测深度.本文方法的估算结果不受模型层厚薄,或目标层与围岩电性差异小等因素影响,因而具有较高的实用性.文中的结论对时间域航空电磁系统设计有理论指导意义,也可用于其它时间域电磁勘探系统探测深度的估算.
The detection depth of the time-domain aeronautical electromagnetic system is a key technical parameter, which plays an important role in the system design and data interpretation. When the difference between the target layer and the surrounding rock electrical conductivity or the abnormal response caused by the target layer is not obvious, In order to overcome this defect, a method of estimating the depth of the system is proposed. By simulating the diffusion process of the electric field in a homogeneous half-space model and a layered model, the maximum electric field is recorded The amplitude is in the underground instantaneous position, and the detection depth of the system is defined as the depth corresponding to the maximum value of the induced electric field in the underground medium at the corresponding moment when the observed response value is equal to the given noise level. Helicopter time domain airborne electromagnetism system CHTEM-I is taken as an example. Based on the analysis of the calculation results under different conditions, the relationship between the depth of investigation and model conductivity, flight altitude and noise level is given and some conclusions can be drawn The results show that the conductivity of the half-space model is in the range of 0.000295 ~ 0.0422S / m, CHTEM-I system can be The sound level reaches the detection depth of 300m under the condition that the sound level is proportional to t-0.5.The estimation results of this method are not affected by the thickness of the model layer or the small difference between the target layer and the surrounding rock, which is of high practicality. The conclusions are of theoretical guidance to the design of time-domain aeronautical electromagnetic system, and can also be used to estimate the depth of exploration of electromagnetic surveying systems in other time domains.