Study On Inversion Methods And Applications Of Frequency-domain Airborne Electromagnetical Data

Frequency-domain airborne electromagnetic method has the advantages of low cost,high efficiency and strong geomorphic adaptability.In addition to providing electrical parameters of underground space,it can also be widely used in various geological survey fields,such as mineral,hydrology,environment,engineering,etc.,to support the rational development and utilization of natural resources and the sustainable development of ecological environment in China.In this thesis,the principles of fast imaging,one-dimensional layered inversion and 2-dimensional inversion methods in frequency-domain are studied firstly.Then,the application comparison of the three inversion methods is carried out by using the typical measured data of high-quality domestic HDY series three-frequency airborne electromagnetic system in Inner Mongolia.Based on the apparent resistivity conversion,the fast imaging developed for the three-frequency airborne electromagnetic system can directly reflect the electrical property changes of the geoelectric section,and it's very suitable for the interpretation method of three-frequency airborne electromagnetic method.The Brent method for 1D layered inversion has the advantages of high computational efficiency,stable convergence and so on.In 2D inversion,the forward model computation is based on an isoparametric finite-element formulation withquadratic basis and test functions.A direct frontal solution method is used to solve for the along-strike components of magnetic and electric fields in the Fourier domain.The sensitivity matrix computation is based on an adjoint equation method which requires one additional source computation for each receiver position.The damped eigenparameter approach is utilised to regularise the inversion process.The number of the inversion parameters can exceed the number of data points.Based on the assumption of layered model,the relatively smooth model can be inverted without any constraint conditions in this method.In a word,any inversion method needs to be tested in practice,and each method has its advantages,disadvantages and applicability.Finally,the fast imaging,1D inversion and 2D inversion are introduced into the interpretation of the measured data of the key airborne electromagnetic anomalies in Erenhot-East Ujimqin Banner area,and the application effects of the three methods are compared.The results show that fast imaging can quickly and effectively provide a large number of underground electrical distribution information,1D inversion can provide the stable inversion results with a certain depth,and two-dimensional inversion has an advantage of obviously better horizontal and vertical resolution.