Research On One-dimensional Forward And Inversion Of Airborne Electromagnetic In Transition Frequency Band

In recent years,people pay more and more attention to the exploitation and utilization of urban underground space and the prevention and control of environmental pollution.The society has a wide demand for near surface detection technology.The traditional frequency domain electromagnetic method has low emission frequency and large detection depth,but its resolution to near surface is low.The early signal of time domain electromagnetic method is generally disturbed by primary field,which lead to a blind area for underground shallow detection.GPR method has high working frequency and high resolution,but it can only detect a few meters underground.In view of the above problems,this paper selects the transition frequency band(1 k Hz ? 1 MHz)which is between the traditional frequency domain electromagnetic method and ground penetrating radar to study the one-dimensional forward and inverse electromagnetic response near the surface,so as to build a foundation for the development of airborne frequency domain shallow electromagnetic detection system.The main research contents are as follows:1)The calculation formulas of electromagnetic response of various configurations in frequency domain airborne electromagnetic detection method are studied.Different from the traditional frequency domain electromagnetic method,which only studies the resistivity(without considering the influence of permeability in non-magnetic medium),the calculation of permittivity is added.The calculation of Hankel integral in the formula is realized by digital filtering method,and the effectiveness of the calculation is verified.2)Through one-dimensional forward calculation and simulation analysis,the horizontal coplanar configuration is selected,and the characteristics and action frequency band of displacement current effect under uniform half space and layered half space are analyzed.In high frequency band,the influence of displacement current must be considered,and the reduction of flight altitude and the increase of transceiver distance will mostly enhance the influence of displacement current effect.3)By calculating the relative abnormal response of two typical hydrogeological models,the detection depth of airborne electromagnetic in the transition frequency band is analyzed,the necessity of displacement current to calculate the relative abnormal response is studied,and the effects of flight altitude and transceiver distance on the detection depth are analyzed.4)the argand diagram with permittivity and resistivity as parameters is obtained,and the rapid extraction of apparent permittivity and apparent resistivity is realized through interpolation algorithm.The inversion of resistivity and permittivity of layered earth model is realized by using damped least square inversion method,and the effectiveness of the inversion method is verified by theoretical and noisy model.