地面与半航空瞬变电磁法三维联合反演

Three-dimensional joint inversion of ground and semi-airborne transient electromagnetic method

半航空瞬变电磁法(SATEM)因其具有工作效率高、探测成本低等优势,成为了一种发展迅速的新兴地球物理探测技术.基于一维反演的SATEM数据处理方法难以满足复杂地质条件下精细解释的需求.同时,采用单一的探测方式,存在探测能力有限、反演多解性强等问题.本文开发了适用于地面瞬变电磁法和SATEM的三维反演及联合反演算法.正演采用基于非结构化四面体网格的矢量有限元法,可以精确模拟地形和复杂地电结构.反演采用具有较高收敛速度的高斯-牛顿法.通过对理论模型分别进行地面瞬变电磁、半航空瞬变电磁单独反演及其联合反演,验证了反演算法的有效性.通过对比不同装置的单独反演结果,以及单独反演与联合反演结果,分析了不同装置的探测能力,并展示了联合反演可以有效压制反演多解性、提高反演结果分辨率的优势.

The semi-airborne transient electromagnetic method(SATEM) has become a rapidly developing geophysical technology due to the high efficiency and low cost. The one-dimensional(1 D) interpretation and inversion method may lead to wrong geological interpretation in the situation with complex geological structures. At the same time, the resolution and exploration depth of different electromagnetic exploration methods are also limited by their survey configuration since each method can only illuminate the subsurface from a specific angle. It is beneficial to reconstruct the subsurface geo-electric structures from the combination of different electromagnetic methods. In this paper, we present a joint inversion approach for the ground transient electromagnetic method(TEM) and the SATEM method. The forward modeling is based on the vector finite element method with unstructured tetrahedral mesh, which can accurately simulate the topography and complex geo-electric structures. We adopt the Gauss-Newton method, which is characterized by fast convergence rate, to minimize the parametric functional. The effectiveness of the inversion algorithm is verified through the separate inversion of the ground TEM and SATEM data and the joint inversion for two synthetic models. Comparing to the separate inversion, the joint inversion can better recover the location and geometry of the subsurface anomalies. In addition, the artefacts are also suppressed in the joint inversion.