Studies On Direction Of Arrival Estimation Of Underwater Targets And Robust Adaptive Beamforming Method

The horizontal hydrophone array for underwater target detection,location awareness and the line spectrum feature extraction,has important applications in passive sonar.According to the working mode of passive sonar,this dissertation studies the super-resolution DOA estimation algorithms in different marine noise environments and robust adaptive beamforming for both narrowband and broadband signals.These research works are able to provide effective technical support for DOA estimation and line spectrum extraction of underwater targets.The main contributions are as follows:1.The model of narrowband and broadband array aignal processing is established,and the sparse signal processing model based on sensor array is presented.Meanwhile,two kinds of broadband beamforming methods are discussed—frequency domain implementation method based on subband beamforming and time domain implementation method based on finite impulse response filter.2.Under the white noise background,a DOA estimation algorithm named the power factor variable Sparse Asymptotic Minimum Variance?SAMV-??is proposed.The super-resolution DOA estimation,ultra low side lobe and coherent processing performance of SAMV-?algorithm are able to be obtained after altering the power factor of the algorithm in each iteration by means of a compromise parameter which is used to compromise the maximum likelihood estimation and the sparse performance of directional spectrum.The performance of SAMV-?algorithm is improved by about 3dB compared with SAMV-1algorithm in terms of the resolving power of adjacent sound sources.The performance of DOA estimation of SAMV-?algorithm is also verified by the sea experiment results,which can provide a clearer Bering-Time Recording map.3.A directional background noise sparse spectrum fitting?DBN-SpSF?algorithm is proposed to estimate the spatial spectral from the covariance matrix in a directional noise environment.The ambient noise at any two different sensors,in practice,may correlate with each other,and the spatial distribution of ambient noise intensity may be directional because of wind and shipping noise sources.A linear harmonic noise model is considered in this study to appropriately describe the ambient noise.By applying l₁-norm penalization of fitting the source covariance model to the estimated spatial covariance and the linear harmonic noise model,a directional background noise sparse spectrum fitting algorithm is proposed.Then,the influence of the regular parameters and the number of linear noise model on the performance of the algorithm is discussed by computer simulations.The performance of the proposed algorithm is verified by the data processing of the sea trial data.4.A super-resolution DOA estimation algorithm under strong interference environment is proposed.The strong interference environment,for example,the tow-vessel noise is a typically strong interference for the towed line array sonar system,which will mask the underwater targets or influence the localization accuracy.Design criteria for matrix spatial filtering based on both narrowband and broadband signal is discussed.Then,sparse signal model is used to fit the covariance matrix of the output sequence of matrix filter and a sparse spectral fitting algorithm based on spatial matrix filter?SpSF-MF?is proposed.Comparing with the traditional methods,the properties of interference suppression and high resolution of localization are verified by both simulations and experimental results.5.A low side lobe robust time domain broadband adaptive beamforming algorithm is proposed.Through the research and comparison of several narrow band robust adaptive beamforming techniques,such as robust adaptive beamforming of diagonal loading,the covariance fitting for robust adaptive beamformer,fully automatic robust adaptive beamforming and low side lobe adaptive beamforming with sparse constraint,a low side lobe robust time domain broadband adaptive beamforming algorithm is proposed and both performance of interference suppression and side lobe suppression are achieved simultaneously.Then the performance of the proposed method is verified by both computer simulations and experimental data processing on Lake.Though data processing of a sea trial by a towed array of the South China Sea,the working mode of passive sonar based on DOA estimation is tested and verified.The DOA estimation can be achieved by applying the SAMV-?algorithm.After designing the low side lobe time-domain broadband beamforming pointed to the multi object orientation estimated from the Bering-Time Recording?BTR?,the diagram of low-frequency acquisition and ranging?LOFAR?can be drawn.Then,the line spectrum information of underwater targets can be extracted though the Hough transform of the LOFAR diagram.