Research On Inversion Technology Of Underwater Buried Target Based On Active Electric Field

The inversion technology of underwater buried targets based on the active electric field can effectively reconstruct three-dimensional images of metal and insulator targets.It uses an excitation source to generate a low-frequency active electric field.The electric field signal received by the electrode array is combined with an inversion algorithm to reconstruct the conductivity distribution of the observation area,thereby realizing the detection and imaging of underwater buried targets.Compared with underwater acoustic and magnetic anomaly detection technology,active electric field inversion technology can distinguish underwater buried targets with different electrical characteristics and has the advantages of simple equipment and low cost.This technology can be applied in military and civilian fields such as submarine oil and gas pipelines,underwater cables,and submarine unexploded object detection,which has good scientific research value and wide application prospects.The main research content of this article includes the following aspects:1.The inversion method of underwater buried target based on active electric field is described.First,the control equation of the underwater low-frequency active electric field is established.Then use the staggered grid finite volume method to discretize the control equation,and obtain the underwater electric field distribution forward model by solving the matrix equation.This paper uses a two-dimensional planar electrode array to collect underwater electric field signal,and then constructs the objective function of the inversion problem based on the forward model and electric field acquisition data.Finally,by solving the objective function of the inversion problem,the three-dimensional image of underwater buried targets is reconstructed.2.The objective function of the lp norm form inversion problem is constructed according to the sparseness of the buried target structure.And the lawson function combined with the PDIPM is proposed to solve the objective function.To solve excessive calculation and storage space resource occupation caused by sensitivity matrix and Hessian matrix explicit calculation and storage,the Newton-PCG algorithm based on the vector product of the implicit sensitivity matrix is introduced.In this dissertation,the inversion effect of the objective function of different lp norm forms is studied through numerical simulation.The results show that for underwater buried targets with sparse distribution characteristics,the use of the lp(0≤p≤1)norm regularization term can effectively preserve the boundary characteristics of the target.For inversion scenarios with abnormal data,the target inversion results and robustness based on the l1 norm error function method are better than the traditional l2 norm error function method.3.The shape inversion and reconstruction method based on PLS function is proposed,aiming at specific scenarios where the conductivity of underwater buried targets and the surrounding environment is binary.It uses RBF interpolation to represent the level set function,and transforms the target and background conductivity distribution problem into a PLS parameter estimation problem,thereby reducing unknowns and reducing the dimension of the inverse problem.On this basis,the IMQ regularization constraint and depth weight matrix are introduced to solve the problem of low vertical resolution in open-domain inversion.At the same time,in the case of large abnormal data in the measurement data,the l1 norm error function is used to construct the objective function of the inversion problem,which reduces the influence of abnormal measurement data on the inversion results and further improves the stability of the inversion algorithm.4.The Newton-PCG iterative algorithm based on the Green function preconditioning operator is proposed,which further improves the solution speed of the underwater buried target inversion problem.From the perspective of the active electric field forward model,the algorithm uses the Rasnow potential energy perturbation model to simplify the forward model.According to the Green function in the model,the approximate sparse matrix of the sensitivity matrix is obtained,which is used to construct the preconditioning operator.The solution performance of different preconditioning operators in the Newton-PCG algorithm is studied by numerical simulation.The simulation results show that the preconditioning operator based on the Green function can effectively improve the speed and stability in the process of solving the underwater buried target inversion problem.5.The underwater buried target inversion system with a two-dimensional planar electrode array is designed based on the theoretical research of active electric field inversion for underwater buried targets.The system consists of an active electric field excitation module,a high-precision multi-channel voltage data acquisition module,a two-dimensional planar electrode array,and a host computer software platform.It can realize underwater active electric field excitation,electric field signal acquisition and target inversion.This paper carried out experimental tests to simulate underwater buried metal pipelines in an experimental pool.The experimental results show that the target inversion system can recover the buried metal pipelines,verifying the effectiveness of the target inversion method based on active electric fields.Finally,the research work is summarized,and the problems that need to be studied in the future are pointed out.