A Research of the Effect and Correction Method about Shallow Inhomogeneous Bodies in High-Density Resistivity Method

Abstract: High density resistivity method is a branch of electric method, which based on the electric difference of the medium reflected by the resistivity data. So, the object can be detected as the lithology difference by difference of resistivity. Therefore, the resistivity difference would not always existed as expected, any changes of resistivity could result in the changes of measured data. This changes could cause the resistivity curves by noise, distortion, and so on, which would decrease the precision of detection.The shallow inhomogeneous medium resistivity can be defined as an inhomogeneous body and all the inhomogeneous bodies can result in resistivity changes, especial the shallow ones. Shallow inhomogeneous bodies cause the distortion of the curves, and make it difficult to recognize the deep objects wakenning and covering up the resistivity changes. This paper is focusing on the effect of shallow inhomogeneous bodies and the correction method of it.In chapter 1, the background and significance of the research and the related research at home and abroad, were introduced. In chapter 2, the basic principles and the methods of high density resistivity method were introduced. And the effect of the shallow inhomogeneous bodies was introduced in detail in chapter 3. Firstly, the forward simulation mode with a single or several inhomogeneous bodies was built on the base of high and low resistivity with RES2DMOD which was developed by Loke in 1999. By the simulation, high density data were obtained under different pole configuration, with which the rule of the effect was concluded. The through the analysis on the data mentioned above, the rule was tested. Last, the theoretical basis for the correction method was built according to the basic principles of the distribution of the underground electric field.In chapter 4, the frequently used correction methods such as ratio method, multipoint smooth method and mean value smooth filtering were introduced, and the simulation data and collected data were compared. The result of the Comparation indicates that the above methods were not satisfactory, a new effective and precise method were needed.In chapter 5, by large account of calculations, a lelements-3 points interpolation method which could greatly decrease the errors, as well as mean value spatial filtering method which could stress the difference and decrease oblique distortion and random errors and the method of second order difference which could indicate the effect range and correct the effect were delivered. Finally, a serial of correction was concluded. Tested by 4 experiments in chapter 6, the correction methods were proved to be able to decrease the effect of the inhomogeneous differences and recovering the deep resistivity data.In general, based on the analysis of the basic principle and the simulation data effected by the inhomogeneous difference under different pole configurations, the principle and characteristics of the effect were concluded. A serial of correction methods were introduced by comparing with the traditional methods according to the characteristics of the effect to the high density resistivity method. The serviceability of the method was tested by correcting the simulation data and field collected data…
Key words: High-Density Resistivity Method; Shallow inhomogeneous bodies; Spatial Filtering; Second-order Difference; Smooth Filtering

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