| Airborne transient electromagnetic method has got rid of the limitation of terrain for geophysical detection.Compared with ground exploration method,this method also has the advantages of high detection efficiency,wide detection area,and low detection cost.Airborne method is one of the main geophysical detection methods currently.Because the frequency points collected by this method are very dense and the area of the measurement area is relatively large,the data volume of this method is also relatively large.This also puts forward high requirements on the methods of aviation transient electromagnetic data processing.At present,the processing methods of aviation transient electromagnetic in practical applications are mainly rapid imaging and one-dimensional inversion.Although there have been major breakthroughs in the research of forward and backward in 2D and 3D,these methods all have high requirements on computing equipment and complex algorithms,which are difficult to apply to practical applications.Based on the theory of electromagnetic field,this paper derives the integral equation of aviation transient electromagnetic electromagnetic response.Then,by changing the model parameters and observation parameters,the characteristics of aviation transient electromagnetic geomagnetic response are studied.After that,the principle of rapid imaging with the chart method is introduced,the shortcomings of the method are analyzed,and the "dichotomy" is used to improve it,and the improved imaging method is tested.In the aviation transient electromagnetic one-dimensional inversion method,the damped least squares algorithm and the Occam inversion method are introduced respectively,and the advantages and disadvantages of the two inversion methods are compared.Finally,the influence of the initial model on the inversion results is discussed.The specific work content is as follows:(1)The integral equation of aviation transient electromagnetic electromagnetic response is a semi-analytical solution equation.This equation can only be obtained by numerical simulation.In this paper,the first-order Hankel is used to obtain the calculation formula of the frequency domain of aviation transient electromagnetic,and then the frequency domain signal is converted into the time domain by the frequencytime conversion method.Considering the large amount of data for aviation transient electromagnetic processing,the frequency-time conversion method adopted in this paper is G-S conversion.(2)By changing the model parameters(resistivity,layer thickness),the response characteristics of aeronautical transient electromagnetic in a typical geoelectric model are studied.Then by changing the equipment parameters(the flying height of the aircraft and the size of the magnetic moment of the transmitting coil),we can understand the influence of the changes in the equipment parameters on the received signal strength.(3)Introduced the common method of conductivity-depth imaging-chart method and the "binary" problem of this method.Based on the graph method,it was improved by the "dichotomy" method,and the forward data was used as the measured data to verify the improved method.(4)One-dimensional inversion of aviation transient electromagnetic.The principles of damped least squares and Occam's inversion method are introduced,which involve the problem of finding the Jacobian matrix and the selection of regularization factors,respectively.The inversion calculation of the geoelectric model verifies the effectiveness of the inversion method,and compares the results of the two inversion methods to understand their respective advantages and disadvantages.Finally,the effect of the initial model on the inversion results is analyzed,and the effectiveness of using the fast imaging results as the initial model for the inversion accuracy and speed improvement is verified. |
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