Fcsem Field Near The Source Of Three-dimensional Non-uniform Body Distortion Characteristics And Calibration Methods

As we all know, with the controlled source frequency Electromagnetic development, the "source effects", including near-field effect, transmitter overprint effect, shadow effect, become more and more complicted, expecially in the responses of three-dimensional(3-D) structures due to a grounded electric bipole confirms. Many domestic scientists brought forward much good methods to deal with the near-field effect, and formed their own theoretics. Iterative method and the digtal approximated were introduced, all those was based on the method of transition triangle of company of phenix in canada. However, the reseach is on going to research source overprint effect and shadow effect in the high dimension. Now we only knew it was exist, but the law of influence and the method of correction would be studied further.Therefore, it was very significant to investigate the response of three-dimensional with uneven body near the field in the controlled source frequency Electromagnetic. So the modeling software "FCSEM "which was based on integral equation was introduced.The distortion characteristics of three-dimensional inhomogenous which were laid near the field through simulating the anomaly body size, depth, and difference in resistivity between inhomogenous and the background have been summerized, which were studied by the all-time apparent resistivity of horizontal electric field component. With the inhomogenous of the location, size and resistivity changes, the shift source effects, could be seen from the analysis of the characteristics of the distortion effect which was described in our traditional static shift have similar characteristics, but this kind of effect and the traditional static shift was somewhat difference. Only when the excitation sources A, B were all laid on the inhomogenous, the characteristics of source effect and the traditional static shift are consistent. when the source AB was partly laid on the inhomogenous, the effect was shown comprehensive influence by the local inhomogenous and static shift. Due to this feature looks like static shift, so we will call this above effects as source static shift so that we can deal with static shift of sources with suppressing the traditional static shift method.Then, the source shadow effect were analysed. And the distortion characteristics of three-dimensional inhomogenous have been summerized through design different models from their size, resistivity, burying and the distance away from the source. All those phenomenon was attributed to the nonsurface wave, it means the ground wave. Further more, a new approach of correctiving source shadow effect was introduced in this paper. Because shadow effect distorts was caused by the ground wave, and the potential magnitude of the distortion could be estimated by the proportion of ground to surface waves. Letβ=ground wave/surface wave. When the ratio was greater than 10%, then we must subtract the k times ratio of ground wave to suppresse it from the total power. Then the purpose of filtering out the shadow effect was carried out. In this paper, K was 0.1.Finally, theoretical models and experimental data, were used in the filtering method and the suppression of ground wave method. While recognizing that such effects is still not well correction method unless more than the source excitation, three-dimensional observation, all three-dimensional inversion is the future development.