Conductance-depth imaging of airborne TEM data
Conductance-depth imaging of airborne TEM data
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DOI：
10.1071/eg993655
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发表时间：
1993-12
影响因子：
0.9
通讯作者：
Guimin Liu;M. Asten
中科院分区：
文献类型：
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作者：
Guimin Liu;M. Asten
最近，许多电导深度成像技术被开发出来用于处理瞬态电磁数据。由于阶跃电流源，这些技术需要磁场数据。然而，目前商用机载TEM系统采用半正弦脉冲源。为了将电导深度成像技术应用于航空数据，需要反褶积将数据转换为所需的阶跃函数响应。由于数据中有噪声，这种反褶积可能不稳定。此外，在导电覆岩地区，系统响应主要是覆岩电导的函数。覆岩的电导率和厚度不能单独求解。系统响应也可能非常高，以至于“半空间视电导率”无法定义，或者电导率图像必须非物理地延伸到地球表面以上才能拟合数据。为了克服上述问题，介绍了电导深度成像方法。该方法基于水平薄板模型，具有简单的解析解。通过拟合两个相邻时间通道的测量数据，利用迭代最小二乘法求出了薄片的电导和深度。然后，瞬变电磁剖面数据可以作为电导-深度剖面进行初步解释。该技术已经过测试，在模型和现场数据上具有鲁棒性。以处理现场数据为例，说明了电导-深度成像技术在矿产勘查中的作用。
Recently a number of conductivity-depth imaging techniques have been developed for processing transient EM data. These techniques require the magnetic field data due to a step current source. However, current commercial airborne TEM systems employ a half-sine pulse source. To apply the conductivity-depth imaging techniques to airborne data, deconvolution is needed to transform the data into the required step function response. This deconvolution may be unstable with noise in the data. Furthermore, in areas of conductive overburden, the system response is mainly a function of the conductance of the overburden. The conductivity and thickness of the overburden can not be resolved uniquely. The system response may also be so high that "halfspace apparent conductivity" is undefined or the conductivity image has to be unphysically extended above the earth surface to fit the data. To overcome the above problems, a conductance-depth imaging method is introduced. The method is based on the horizontal thin-sheet model which has a simple analytical solution. By fitting the data measured at two adjacent time channels, the conductance and the depth of a thin sheet are found using the iterative least-squares method. Transient electromagnetic profile data can then be presented as a conductance-depth section for preliminary interpretation. The technique has been tested and found to be robust on model and field data. An example of processing field data is used to demonstrate the capabilities of the conductance-depth imaging technique in minerals exploration.