Inversion And Application Of Frequency-domain AEM Data From A Layered Earth

Airborne electromagnetics (AEM) has been widely applied in geological mapping, mineral exploration, geohydrological investigation, engineering and geological environmental monitoring. AEM can be used in forest, desert, swamp, lake and residential area which is difficult to use ground geophysics based on its low cost, high efficiency and adaptability. AEM is the absolutely necessarily method in geological investigation and mineral exploration, especially in reconnaissance. AEM has been widely used as a conventional geophysical method overseas. The following has been studied for data process and interpretation of the triplex-frequency AEM system: 1. A few new apparent resistivity transform methods have been systematically studied. The understanding to every apparent resistivity transform methods has been improved after theoretical modeling computation, analysis and discussion. In addition, some of the apparent resistivity transform methods can be used in fast approximate inversion and automatic inversion. 2. Fast approximate inversion method for the triplex-frequency AEM system is firstly developed. Based on the theory of skin depth, we obtain the empirical formulae that adapt to the triplex-frequency AEM system after modeling. The apparent resistivity parasections derived from the triplex-frequency AEM data of 1-D models have been developed for the first time. The parasections can outline the resistivity changes. It is the basis of starting model for automatic inversion. 3. A new Brent algorithm has been used to solve nonlinear equations. Compared with conventional methods, this algorithm has high efficiency, stable convergence with wide initial value. It's a promising inversion method. 4. The principle of instituting starting model has been found after analyzing the relation of apparent resistivity, apparent thickness and parasections derived from triplex-frequency AEM data based on modeling . Then the automatic inversion is realizable. 5. The apparent transform, fast approximate inversion, Brent algorithm and automatic...