Research On Focusing Theory Of Marine Controlled Source Electromagnetic Method

The marine controlled-source electromagnetic method(MCSEM)obtains electrical differences in the submarine stratum structure by measuring the electromagnetic field of artificial sources in the seabed space to identify abnormal information.However,the traditional MCSEM method is greatly affected by the environment,and it is seriously interfered by air waves in shallow water.For complex geological targets,it is difficult to identify abnormal information using MCSEM data only.At the same time,the development of marine electromagnetic detection instruments is difficult,and the key technology is immature,so the detection result is not accurate enough.In order to enhance the abnormal signals and reduce the adverse environmental impacts,this paper carry out the focusing theoretical study of marine controlled-source electromagnetic method based on the synthesis of domestic and foreign scholars' research on the marine controlled-source electromagnetic method.This theory aims to highlight the abnormal signals and improve the ability to detect anomalous bodies by optimizing the combination of electromagnetic field data excited by multiple sources without changing the acquisition method and increasing the exploration cost.This article first introduces the synthetic aperture focusing method,which uses the idea of synthetic aperture radar to perform relevant superposition processing on the electromagnetic field data excited by multiple emission sources to focus the electromagnetic field energy on the abnormal bodies' region and enhance the abnormal response.In this paper,the optimal amplitude and phase correction coefficients of the synthetic aperture are selected experimentally,several theoretical models are established and the electromagnetic field data excited by multiple emission sources are obtained.By comparing the abnormal normalized curves before and after synthesis,the results show that the synthetic aperture focusing method can effectively improve the anomaly response and enhance the ability to detect anomalies.In order to further improve the abnormal response,this article introduces the principle of focusing optimization algorithm and uses it to optimize the combination of data.The algorithm is based on the synthetic aperture,using the regularized conjugate gradient method and the occam method to solve the objective function minimization problem to find the best data weights,and more scientifically superimposes the electromagnetic field data of multiple emission sources.For the same theoretical models,using the focusing optimization algorithm obtain the abnormal normalized curves and compare with the abnormal normalized curves obtained by the synthetic aperture focusing method.The results proved that the focusing optimization algorithm can more effectively improve the abnormal response and enhance the ability to detect anomalous bodies.Based on the above research process,a focusing imaging theory and method with stronger resolution ability for anomaly information can be obtained,which is more powerful than traditional MCSEM in suppressing air waves,enhancing weak signals from deep seafloor,and resolving different anomalous bodies.