【作者】 朱威；

【导师】 李桐林；

【作者基本信息】 吉林大学 ， 地球探测与信息技术， 2009， 硕士

【摘要】 大地电磁二维反演,虽然已经有了很多很成熟的算法,但是在反演精确度和可靠度方面各种方法的差异很大,如何寻找到一种更有效和更精确的反演方法,一直是广大地球物理工作者努力研究的方向。本文主要基于OCCAM反演方法,研究通过使用图像编辑技术设计二维地电模型,从而进行二维大地电磁有限元数值模拟及二维大地电磁反演,以提高解释速度。OCCAM反演方法无需人为分层,结果也和初始模型关系不大,且反演时收敛稳定,对反演人员的要求不高。且在适当的初始模型条件下,反演效果会更加理想。因此,本文采用VB编写图形编辑界面,构建正演模型和不同反演初始模型,以减少针对特定程序不断修改正、反演所需要的数据和数据类型的繁琐过程,提高模型构建速度;Fortran编写大地电磁测深有限元数值模拟以及反演的计算程序,由于计算程序中各种输入输出参数比较多,且VB和Fortran通用的数据类型较少,为了避免错误,采用文本传递方式解决参数传递问题。同时用两种方式实现对Fortran程序的调用,一种是应用动态链接库调用(DLL),另一种是直接调用Fortran生成的可执行程序。人机交互对模型的编辑更加直接,可以在想要深度的地层编辑任意形状的地质体,同时可以实时的显示对构造模型的响应,提高了解释速度。更多还原

【Abstract】 For two-dimensional MT forward and inversion procedure not only cockamamie in the editing of geological model, such as manually edit the grid and give the resistivity of underground geological model and so on, but also is due to the model editing and the results of forward and inversion show in different systems, so we would be expend correspondingly longer cycle to get the results of forward and inversion, That would be serious impact the efficiency of the interpretation.In this paper, through research two-dimensional forward and inversion of MT and two-dimensional model of the image editing techniques ,to use the VB and Fortran mixed programming technique developed the two-dimensional MT interpretation system based on OCCAM inversion, provided the prior model parameters to reduce the multiple solutions of the inversion results. Speed up the efficiency of the interpretation.Two-dimensional MT forward imitated by using simplified Maxwell equations export two wave equations, that is, Helmholtz equation. Using Finite element method to solve this equation, First, differential equations and boundary conditions will be transformed into functional extremum problem, then gridded the solving regional and using the linear interpolation method to indicate the value in functional by node value, take a very small value on the nodes of the system of linear equations, solving the linear equations obtained the value of each node, and then calculate the value of auxiliary field, which has been lucania resistivity.In this paper, written in Fortran geoelectric model of the two-dimensional magnetotelluric forward OCCAM inversion process and procedures, and compile dynamic link library for use VB language to explain the design of interactive interaction system interface, by calling the dynamic link library to VB and Fortran language combination. In the dynamic library calls to use the disk version of transmission, a parameter to overcome the shortcomings of red tape, reducing the demand for memory, saving system resources. Fortran procedures for calculation of input and output all the way to adopt the text, graphical interface from VB to provide the input parameters, also stored in the text, read for the forward calculation, the end results of the calculation stored in the text, by VB read the results in the form of image rendering display.OCCAM principle method is to find structure in the sense of the minimum possible consistent with the data model, a model defines the roughness, in order to suppress data from non-model construction, model of the roughness must be minimized. Method is characterized by OCCAM at each iteration in the parameterλ, not only as a step size control parameter, but also as a smoothing parameter. At each iteration of the single variableλsearch to find the smallest difference data fitting the model, as the next iteration of the model, poor fitting until it reaches the level of expectations. OCCAM law for the use of finite element forward modeling, with an increase in the scale model, the matrix inversion will occupy most of the time, and increase the frequency of measurement than increasing the number of points on the inversion of time a greater impact, but to increase their forward little impact on computing time. OCCAM law and the use of Cholesky decomposition of positive definite symmetric matrix in the inversion, it is not the fastest speed, but very stable.Inversion method by comparing the RRI, OCCAM inversion approach requires that the input parameters small, high efficiency, high precision, stability and inversion algorithm staff do not ask for much and so on. From the calculation speed and convergence of circumstances, the appropriate limit of the model can achieve better results. OCCAM simulation in the pursuit of the original measurement data and fitting curve of the largest at the same time, the most requested model data or the most sleek smooth and stable convergence can be achieved. Results from the inversion, OCCAM inversion to better reflect the bodies of the underground geological features of electricity distribution, in order to explain the results to provide more reliable reference information, is a better tool to explain the inversion.In the Interactive Interaction system development processing, the solution including the dynamic library calls, coordinate transformation technology, mesh generation technology, the graphical model display and editing techniques, the results of the mapping curve, etc.. The realization of the model zoom, pan, a single unit and regional resistivity assignment functions. VB procedure of the functional definition of the subroutine, when necessary to call these routines to increase the utilization rate of the code at the same time enhancing the capacity of the secondary development of the system. Interactive interaction system is mainly explained by the menu bar, toolbar, model and curve areas, tab, select the color box with the resistivity value of these parts. The system functions mainly through the operation to achieve the mouse, the menu bar and toolbars to provide conversion between the various functions as well as the model to open and save. The system functions mainly through the mouse operation to achieve, to the various functions in mouse operation, determine the need to address the issue of function, various functions of the code used to that in operation when the mouse to determine the function of the need to implement the code, so to solve a variety of functions to achieve through the mouse problem.To use interpretation system editing the model is valid, simple and quick, solve the problem that manual input would be cumbersome and error-prone shortcomings, when the model was changed, the corresponding c calculated results will be displayed real-time, so the data processing cycle was shorten, improve the work efficiency. In the system different colors shows different resistivity , editing the model could choose the depth and horizontal position corresponds to a single unit, you can select multiple unit volume editor, intuitive to understand, and convenient. Model can pan and zoom, the overall resistivity of the model distribution and the local resistivity can edit the details, the scaling curve can make the overall curve shape and the local details can be a good show. Another advantage of this system is that the second development ability, are independent of each functional module, as long as other means to provide positive and added new inversion method to the system.更多还原