Study On Forward And Inversion Of Ip Effect From Grounded-wire TEM

A negative response which is caused by the induced polarization effect may appear in the transient electromagnetic measure when the polarized appearing in ground and the IP effect has been confirmed by a lot of research and practical work. The control source induced polarization method with long offset is intrinsically same as nature source induced polarization. The electromagnetic effects are overwhelming superiority to the IP effects. It is very difficult to pick up the week IP effect from the strong electromagnetic response, so the practical application prospects of the control source induced polarization are not optimistic. Compared with frequency domain electromagnetic method can realize a short-offset even zero-offset detection. In this paper the difference in the detection ability between large fixed-loop source and long grounded wire source were compared. The conclusion is that long grounded wire source has bigger detection depth than large fixed-loop source. Long grounded wire source could be observed not only magnetic field component but also electric field component. Therefore, study on characteristic and rules of long grounded wire source response due to the Induced polarization effect and the method of extract Induced polarization information from EM response could solve the deep deposit contain large ore information.This paper describes the origin of Cole-Cole model briefly. The article has carried on 1D Grounded-wire TEM Forward based on the Cole-Cole model and analysis the influence of IP effect from polarization medium resistivity and offset. By changing the Cole-Cole model parameters to compare various components decay curves of transient electromagnetic field through the uniform half space model. The conclusion is that the influence of polarization is the largest, followed influence is frequency coefficients and time constant has minimal impact. Calculating three layers geoelectirc section, the result shows that different types of geoelectirc section affected by the IP effect of different levels. Comparing the characteristic impacts of CSAMT and Electric Source TEM due to IP effect, the result shows that the Electric Source TEM is utilized to extract the IP information has more prospects. In the paper, two definitions of all-time apparent resistivity are introduced as the magnetic field strength method and electromotive force method and compared two all-time apparent resistivity curves.This paper carries out the full-parameters inversion by using the LMF method. The result shows that full-parameters inversion result is highly depend on the initial model parameters. It can get ideal result only when we choose right model parameters. Based on the horizontal magnetic field component in the reflection of the IP effect is not sensitive, we raise inverse another three parameters by fixed frequency coefficient and time constant and take the inversion result as the initial parameters of next step inversion. Finally, we make full-parameter inversion through vertical magnetic field component the method can get ideal result. The damped least square feasible direction method to some extent inhibited the uncertainty of inversion. The result of theoretical study show that the IP affect from Electrical source TEM is remarkable and can be extracted, the inversion result basically agrees well with real parameters.