Research On Measurement Method For Multistatic Underwater Target Strength In Multipath Interference Environment

With the development of underwater unmanned systems and underwater target stealth technology,a single sonar platform is no longer sufficient to meet anti-submarine needs,and multistatic underwater target acoustic detection has become a research hotspot in the field of acoustical engineering.Therefore,in the multistatic scenario,studying the measurement methods of target intensity for different incident/scattered directions is of great significance.Obtaining target intensity results in a multistatic scenario faces various challenges.On the one hand,outfield measurements can provide real models and actual data in the environment.However,the underwater environment is complex and variable,and multipath interference makes it difficult to extract the target scattered wave signal.In addition,the target intensity results obtained by multistatic measurements are affected by measurement equipment position errors,instrument errors,model posture errors,and other factors,leading to measurement deviations from the true values.On the other hand,with the development of large computers,accurate modeling and numerical simulation provide an effective way for incident/scattered calculation of target intensity at high resolution angles.However,due to model errors,numerical calculation errors,environmental modeling errors,and other factors,there are deviations between numerical results and true values.This paper focuses on the research of multistatic target intensity measurement methods for the above issues,mainly including the following aspects.First,theoretical derivation of the echo-forwarding measurement method under multistatic measurement was carried out,and the theory was applied to the outfield measurement of target intensity of submarine scaled model.The experiment was conducted by emitting from multiple incident angles with a fixed sound source and receiving scattered waves around the target by a moving platform in a circular navigation path to measure the target intensity.To address the problem of severe multipath interference on the scattered waves in multistatic measurement,a wideband underwater acoustic channel modeling study was conducted.Based on the sparsity of the channel,signal processing algorithms such as Orthogonal Matching Pursuit and Bayesian learning were applied to extract scattered waves,in order to improve the accuracy of multistatic target intensity measurement.We propose an improved Temporal Multiple Sparse Bayesian Learning（TMSBL）scattering wave extraction method to address the problem of increased errors in existing scattering wave extraction algorithms due to limited bandwidth.The method uses a reweightedl₁ minimization algorithm to obtain initial hyperparameters and a corrected perceptual matrix,and uses the channel consistency and time correlation properties to complete high-resolution estimation of the received signal multipath delay using the TMSBL algorithm.Based on the multipath delay as prior information,a least-squares-based multipath amplitude estimation is performed to separate and extract the multipath signals.Simulation results show that the improved TMSBL algorithm can accurately and effectively extract scattering wave signals in`low-bandwidth signal conditions.In response to the problem of difficulty in accurately obtaining target strength through on-site measurement and simulation calculations,in order to fully utilize the advantages and complementarity of experimental measurement and modeling calculations,we attempt to apply data fusion methods to multistatic target strength measurement.Based on the weight coefficient design of data source error,an adaptive weighted fusion method based on wavelet and a two-stage data fusion method are proposed.The two methods balance the rationality of simulation results and the authenticity of measurement results,improving the reliability of multistatic target strength measurement results.Finally,to verify the effectiveness of the method proposed in the paper,numerical simulation and outfield experiments of multistatic target strength were conducted for a finite length ribbed cylindrical shell model.The scattered wave extraction method with multipath separation was used to process the multipath received signal,and the target strength measurement results were fused with the simulation calculation results to verify the feasibility of the data fusion method.The experimental data processing results show that the method proposed in the paper can effectively extract the direct wave signal and the scattered wave signal under multipath environmental interference,and obtain reliable target strength fusion results.