Research On 2.5-Dimensional Multiparameter Forward And Inversion Of Frequency-Domain Airborne Electromagnetic

Since the beginning of this century,with the development of software and hardware technology,the application of aeronautical electromagnetic method in geophysical exploration has become more and more extensive.However,in terms of inversion interpretation,it still faces great difficulties,mainly reflected in the huge calculation and memory requirements caused by multi-source aviation electromagnetic emissions.Two-dimensional inversion is currently the most likely solution that takes into account both computational efficiency and computational accuracy.Therefore,a research on the 2.5-dimensional forward and inversion of aviation electromagnetics has been carried out.For forward modeling,the 1D and 2.5D forward modeling problems of frequency domain aviation electromagnetics are derived from Maxwell's equations.Based on the unified framework of geophysical forward and inversion,the frequency domain aviation electromagnetic 2.5D numerical simulation program using unstructured finite elements is developed.In order to improve the simulation accuracy,unstructured grid division is used,and techniques such as grid division,field source processing,wave number selection and matrix compression are discussed.In order to improve the efficiency of forward modeling,the direct method is used to solve the forward modeling equation.In addition,a simulation study on the effects of permeability and permittivity has been carried out.The one-dimensional forward results show that the permeability and permittivity will have a greater impact on the aeronautical electromagnetic response under certain circumstances.The influence of magnetic permeability and dielectric constant is considered during the exercise.On the basis of forward modeling,the research of aeronautical electromagnetic2.5-dimensional inversion algorithm is carried out.A regularization scheme is used to design the inversion objective function,and the Gauss-Newton method is used to optimize the objective function.The effectiveness of the scheme is verified on the basis of the unified geophysical forward and backward inversion framework,which is applied to the 2.5-dimensional inversion calculation of DC resistance data.The results show that the inversion algorithm is stable and effective.In order to improve the inversion efficiency,the approximate adjoint method is used to calculate the sensitivity matrix.For the multi-source emission problem in the aeronautical electromagnetic method,the footprint technique is used to divide the inversion area to calculate the sensitivity.In order to improve the inversion efficiency,the sensitivity matrix is solved using the approximate adjoint algorithm.In order to improve the inversion accuracy,the transformation function constraints are introduced,and three typical transformation functions are studied based on the unified framework program,and applied to the magnetic data inversion to obtain good results.Combining the above methods and developing a 2.5-dimensional frequency domain aeromagnetic electromagnetic inversion program on the basis of a unified framework,the inversion results show that the algorithm can effectively reflect underground anomalous structures.