Research And Implementation To 2D Interactive Interpretation System Of MT And DC Method

We developed a 2D interactive interpretation system of MT and DC method through research of finite element forward calculation theory of magnetotelluric and graphics edit technique and DLL in the 2D model.First, through the simplification of the Maxwell's equations, we get two sets of polarized wave equation derived by vertical incident plane wave, that is, Helmholtz equation. Point electrical source field meets stable current field equation, we get differential equations of potential through basic relations of stable current field expression. Point electrical source in 2D model is a 3D problem, but, the calculation of 3-D finite element method to is enormous, and requirements of computer are also high, sowe can transform the 3D problem to 2D problem with parameters by Fourier Transform, that is, equation of transpositional potential with parameter of k . then, it is easy to solve by finite element method . In the end we do the anti-Fourier transform to get normal potential.Electromagnetic fields of MT in two groups of polarize mode and point electrical source field meet the same type of differential equation, that is, Helmholtz equation. This type of equation can be solved using the finite element method, first, differential equations and boundary conditions will be transformed into a functional extremum problem, then, grid the calculate region, replace the function with node value using linear interpolation method, we can get a linear equations by minimize the equation, we obtained all the nodes value by solving this linear equations.We write MT and DC forward calculation program using Fortran Language and transform it to DLL. We develop interactive interpretation system using Visual Basic Language and link Fortran Language and Visual Vasic Language by calling DLL. We pass parameter by text, text parameter is that data of the import and processing be saved to a text file. It has overcome the shortcomings of passing parameters of red tape, it reduces the demand for memory, saving system resources. We take use the way of text through fortran calculation, and we compiled forward calculation program in Campaq Visual Fortran, and VB offer all kinds of parameters which save in the text. And the result of forward calculation are saved in the text. And VB can read the results from the text and draw in the form of images show.In the system development process, we mainly to resolve several key technologies, including DLL technology, coordinate transformation technology,grid technology,the model of the display and imaging edit technology, the results display technology, we carry out the model zoom, pan, a single unit and regional resistivity assignment,the curve of the display, zoom, coordinates of the transformation,scale conversion, and other functions. All the technique can achieve through custom coordinate system which defined of the actual coordinates of the screen and the transformation of relations between the coordinates, and in accordance with the needs we can take of the different functions of transformation, and throught changing the conversion ratio to achieve of zoomin and zoomout and pan, changed into the position can be achieved model of translation. The system provide the coordinates of two ways the linear coordinate and logarithmic coordinates in the draw curve of the result, and also can zoomin and zoomout throught changing the ratio. To show different resistance of models in view way, we take different colours to show different resistivity values. The system defined in the various functions of the subprogram in VB procedures, and when we need we can call these routines, while those can enhance the development of the secondary system capacity.Interactive systems modular design: interactive system is mainly made of the menu bar, toolbar, and the region of model, the tab, selecting the color and resistivity assignment box. Tab used to provide curve parameters, options and other devices coefficient of input; the menu bar and toolbar to provide the conversion between the various functional model and open and save files, all of the system functions can achieve through the operation of the mouse, it gather those functions in the mouse conveniently. But when we use various functions of the code to correspond judgement of the mouse operation, by doing that need to solve the function matter or judgement, this resolves the various functions are operated by the mouse to realize the problem.The main characteristics of this system is that it is visual when edit the Model and form the image, the input of model is very convenient andquick, and also avoided the shortcomings of tedious and error-prone by manual input of the past, The results shows that the corresponding quickly when the model changeing, so it can short the data processing cycle and improve work efficiency, the model showed that in the way of different colors indicate the different rates of resistance. The way of editing model can choose two ways: a single unit or multiple unit quantities, Model can pan and zoomin and zoomout,we can chang the Resistance to the overall distribution model and local resistivity details,and curve zoomin and zoomout it can be a good show as the curve's the overall shape and local details. DC has many types of devices, so the system provides different types of devices chosen to meet the different needs. Another advantage of this system is the second development capability because of the independent of the various functional modules, we can other means add to the system as long as forward procedures are provided.The interpretation system can play multiple roles, first of all, it can be used to solve practical problems by fitting measured data, then ,it can be used to do forward calculation , to establish specific model, we can observe the response of the earth's electromagnetic field and DC electric field in different sections.