Study On Modeling And Inversion Of Airborne Induced Polarization In Layered Media

Airborne transient electromagnetic(ATEM)can complete the resources and environmental exploration in the complex terrain conditions,or harsh climate areas which the traditional ground electromagnetic method is difficult to complete.At present,ATEM has a great development both at home and abroad.Especially in recent decades with the development of time-domain airborne EM system and the improvement of the accuracy of data collection,the relevant staff frequently discovered the phenomenon of sign reversal in the late-time channels among the ATEM response.And it is found by the scholar that the phenomenon is caused by the induced polarization(IP)effect.However,the traditional inversion method based on resistivity cannot effectively interpret and correctly inverse such kind of ATEM data.In the early research,these data,the part of sign reversal in the late-time channels,is usually removed directly during the data processing,and only the early part of ATEM data is explained.The method will inevitably lead to the loss of deep geophysical information and the distortion of the resistivity inversion result.In recent years,the inversion of induced polarization parameters in ATEM has become one of hotspots.The effective solution to this problem has a dual meanings for the development of ATEM and the growth of national economy.Therefore,the main contents of this paper is study on modeling and inversion of airborne induced polarization(AIP)in layered media.In this paper,we first introduce the electrochemical theory of the induced polarization method,and show two typical polarization model.In addition,the Cole-Cole model,which is widely used,is introduced,and its simple transformation is carried out.The range of the IP parameters of several typical rock ores is given,and the frequency characteristics of the ore are analyzed.These laid the theoretical foundation for the follow-up study.We study the IP effect on airborne transient EM diffusion.The frequency-domain electric field component at any position of the full space is given.The frequency-domain current density is obtained according to the Ohm's law.By decomposing the Cole-Cole model,we can get the frequency-domain induced current density and frequency-domain polarization current density.The time-domain current densities are calculated by using the sine or cosine transformation which convert from corresponding frequency-domain current densities.By analyzing the time-domain characteristics of induced current density,polarization current density and total current density,the EM diffusion characteristics in polarizable medium are studied.We also study the charge and discharge process of induced current and polarization current,and give the reason of the phenomenon of sign reversal.By studying the EM diffusion characteristics in different chargeability and conductivity,the influence of different IP parameters on the EM diffusion is obtained.These results provide a good theoretical explanation for the forward modeling of the next chapter.For studying on the AIP forward modeling.We give the vertical magnetic field expression of the layered polarizable medium with the horizontal circular loop source.The AIP response is calculated by using the sine or cosine transformation and the convolution algorithm.It is reasonable to explain the phenomenon of twice sign reversal in the AIP response,through the modeling study of the layered polarization model.Finally,we study the inversion of AIP parameters by using the classic Occam inversion method.The basic theory of Occam inversion method is introduced firstly.And the Cole-Cole model parameters are restrained during the process of inversion,which can improve the stability of inversion and reduce the multi-solution to a certain extent.The inversion of several typical theoretical layered polarization models shows the advantages and limitations of the inversion algorithm.The results of this paper lay a good foundation for the future research work of three-dimensional modeling and inversion for airborne induced polarization.It is helpful to understand the induced polarization effect on airborne transient EM,and these results have a certain theoretical significance.