Study On The Cross-Well Electromagnetic Tomography And Its Application

The theory of electromagnetic field suggests that when the wave transmits in the dielectric the wave will be reflected and refracted going with the energy absorbed. The theory related indicated that the absorption coefficient of electromagnetic wave has relation with the conductivity, magnetic permeability, dielectric constant and the frequency of the wave. Especially, the conductivity is the decisive parameter to the absorption of the energy. Related factors that influence the conductivity mostly include the water saturation, porosity and the karst developing extent and feature in the limestone area.Computerized tomography is a method which makes use of collecting physical datum from the object's exterior and avails itself of some algorithms to computes to make two-dimensional plot. Radon transformation, which is put forward by a mathematician named Radon, is the keystone of the technique. Radon discusses this transformation and proves that if we know the angles of incidence of all the radials, we can inverse the only function of plot. When the frequency of the incidence magnetic wave accord with some qualifications it canbe approximately looked upon transmitting according to line. So, we can make use of it to computerized tomography.Electromagnetic tomography generally adopts two kinds of method that the one reconstructs absolute attenuation and the other reconstructs comparative attenuation. The equations of the two kinds of method are all the same which use the method to inverse absorption coefficient. Differently, the former reconstructs the actual absorption coefficient while the latter reconstructs the comparative coefficient.The problem of electromagnetic tomography can be in the final analysis summed up that it is to solve linear algebraic equations. Nowadays, the algorithms such as algebraic reconstruction technique, simultaneous iterative reconstruction technique, damper least square method and so on. Lately, scientific researchers continually experiment to improve on this issue and enrich the means of analyzing information of computerized tomography. Back projection technique (BPT) needs less EMS memory, computes quickly, without divergence, but its resolution is low. Algebraic reconstruction technique (ART) has high resolution but its anti-noise performance is lower. Simultaneous iterative reconstruction technique (SIRT) is more stabilized than ART but it needs more EMS memory. M-SIRT we always used makes use of the length which through every plot cell as weight and computes the average correctors.When we apply the technique of cross-well electromagnetic tomography to engineering practice the ways we can use mostly include two kinds that synchronous observation measurements and fixed pointed measurements. The former includes horizontal synchronous measurements and acclivitous synchronous measurements. The latter includes fixed pointed emission and fixed pointed acceptance. This thesis at the basis of different data formats of differentobservation measurements adopts the popular computer language C++ and takes advantage of writing the computer program to achieves cross-well electromagnetic tomography plotting. Through carrying out two kinds of arithmetic M-SIRT and BPT from practical example it introduces the program can be applied in many engineering projects.Nowadays, the technique of cross-well electromagnetic tomography is developed as a new popular technique and method. It is mainly applied to dealing with the characters of the cross-well two-dimensional physical model and inversing the distributing of dielectric which contains different absorption coefficient. The technique of cross-well electromagnetic tomography is used in many engineering projects especially in the great projects of geological investigation as dams, bridges, high buildings and so on. We often need to exactly explore and evaluate the safety and stability of the underground and to find out whether it contains the faults and other weak layers. The technique has superior advantages at this field than any other methods. It can also precisely and intuitionally describe the shape and location of the abnormal geological part besides that it can uncover the characters of abnormal body which the general methods can. It can supply us with more particular geological information. Therefore, it offers an effective way in this field.From practice in this thesis it proves that the arithmetic methods of M-SIRT and Back projection technique which are mentioned in the thesis can be applied into engineering projects. Furthermore, the method of cross-well electromagnetic tomography compared with traditional techniques is visually and vividly plotting the geological structure nearby the earth's surface. So we can gain more information of the interior rock and soil. Especially, the method has a good effect on prospecting the faults and fragile strips. The technique takes advantage of quantity of probe data and has a good resolution. So the technique is a supplementary availability to the insufficiency of drilling exploration engineering.