【作者】 李小康；

【导师】 谭捍东；

【作者基本信息】 中国地质大学（北京） ， 地球探测与信息技术， 2011， 博士

【摘要】 航空电磁法(Airborne Electromagnetic Method)是航空物探中常用的观测方法之一,广泛的应用于地质普查、资源勘探和环境监测等领域。本文针对吊舱式直升机频率域航空电磁系统IMPULSE的各方面特点进行深入分析,提出了二维正反演研究的重要性。频率域航空电磁法二维正演问题实际上是,求解三维场源在二维地电断面中引起的电磁响应,也被称为2.5维问题。利用电磁场沿走向以场源中心呈对称分布的特点,可通过沿走向的傅立叶变换将空间域2.5维问题简化为波数域二维问题进行求解。本文首先按照场分离的思路,对一次场和二次场进行分离,通过将背景电导率分布设为全空气介质,使用解析解计算一次场,而二次场则使用有限元法求解。二次场求解过程中,使用伽辽金加权余量法和抛物线等参单元法进行处理。在求解大型线性方程组时,没有对整体刚度矩阵进行集成,而是选择波前法求解,从而避免的对整体刚度矩阵的存储,提高了计算效率。在完成公式推导后,根据得到的算法设计流程图,使用Fortran语言编写了串行代码。精度检验的结果显示,该频率域航空电磁二维正演算法具有相当的可靠性。随后,对8组不同的地下异常体模型和观测装置组合进行正演计算,并对得到的电磁响应结果进行分析。鉴于频率域航空电磁法多维正反演问题的复杂性,并为将来的反演计算打下基础,本文尝试对提出的正演算法进行并行化。Message Passing Interface(MPI)是用于并行编程的一种主要标准和规范,通过对其深入研究和对提出的频率域航空电磁法有限元正演模拟算法的分析,选择了域分解算法设计和SPMD并行编程思路。通过在小型网络机群的测试,正演计算的效率得到了大幅提升。更多还原

【Abstract】 AEM(Airborne Electromagnetic Method)is one of the most commonly used branch of airborne geophysical method, which is widely used in geological survey, recourse exploration, environment monitoring and other related fields. Based on a thoroughly investigation in the features of all aspects of IMPULSE -one of the most popular frequency domain airborne electromagnetic systems, the importance of 2D modelling and inversion of AEM data was revealed. The 2D forward problem of AEM is actually to calculate the response of 2D geoelectrical model to a 3D source, which is also named 2.5D problem. During the practical procedure of calculating, the 2.5D Problem could be reduced to 2D problem through taking a Fourier transform along the strike direction because of its symmetry character on the strike.By using a free space as the distribution of background conductivity, the primary and secondary fields could be calculated separately, one by analytical solution and the other by FEM (Finite Element Method). Galerkin weighted residual method and isoparametric element with quadratic basis were both employed in calculating the secondary field .The system matrix for coupled equations is solved using the frontal solution, which is similar to Gaussian elimination except that the system matrix is never actually assembled and essentially reduce the computation cost. A serial code was developed by Fortran after finishing the formulating. The accuracy and efficiency of the code was tested by an simple layered model by comparing to the analytical solution which turned out to be that the 2D modelling algorithm is considerable reliable. Subsequently, the response of 8 different set of model and configurations were calculated by the code and analyzed for features.As the complexity of multi-dimensional frequency AEM modelling and inversion, parallelized attempt was made on the forward code for inversion consideration in the future. MPI(Message Passing Interface)is one of the most important standard in parallel programming, which leads to a domain decomposition algorithm and a SPMD(Single Program Multi data) idea. A small Cluster was built on which the parallel code was tested and turn out to increase the modelling process dramatically.更多还原