Research On Target Detection Method Based On Seabed Stationary Array

With the enhancement of the status and prominent role of the ocean in the development strategies of various countries,underwater target detection,as an important technical guarantee to maintain marine security,has gradually become a core research topic in the field of underwater acoustic.Underwater environment is complex and fluid.There are many different kinds of interference and noise and the impact of each are not identical.At the same time,target stealth technology develops rapidly.Both in active detection and in passive observation,signals which contains the information of targets may be overwhelmed with strong ambient sea noise and interference so underwater weak target detection becomes more difficult.The seabed stationary array has excellent detection performance in such underwater environment due to its large size,high gain and long time observation.In this paper,the target detection methods based on seabed stationary array are studied mainly from two angles of long-range target Direction-of-Arrival estimation based on large size array under low and unequal signal to noise ratio of each array element and underwater weak target detection based on sonar target spatial and temporal scattergram in low SNR.The effectivenesses of these algorithms are verified by simulation and sea trial test data.Firstly,the common methods of conventional sonar signal processing are studied.Receiving signal mathematic model of seabed stationary array,and target bearing estimation algorithm based on this model under equal or unequal signal to noise ratio of each array element,frequency domain broadband beamforming is presented in this paper.The spatial spectral evaluation index is defined to measure the performance of Direction-of-Arrival estimation algorithms.This paper also expounds the principle and characteristics of sonar target spatial and temporal scattergram in order to provide theoretical basis for further research.Secondly,the long-distance target Direction-of-Arrival estimation methods of large size array are studied.In order to improve the processing gain and the accuracy of Direction-of-Arrival estimation,the difference between noise and signal in the received data covariance matrix is used to study the Direction-of-Arrival estimation method based on the covariance matrix pretreatment,and the bearing estimation technology based on the long-time azimuth stability is studied by using the long-time observation characteristics of the array.In the case of unequal signal to noise ratio,a bearing estimation method based on narrowband sparse representation is studied by using target sparsity,a bearing estimation technique based on noise covariance matrix is studied by using signal to noise ratio homogenization processing technology,and a Direction-of-Arrival estimation algorithm based on subarray azimuth stability is proposed by using array large-scale characteristics.In the case of low and unequal signal to noise ratio of each array element,the method of space-time joint signal processing and compressed sensing is studied by using the large scale and long-time observation of array,and the subarrays combined Direction-of-Arrival estimation based on covariance matrix pretreatment is proposed.Then the underwater weak target detection methods based on sonar target spatial and temporal scattergram are presented.In order to improve the weak target detection performance of sonar in low SNR,underwater weak target detection method based on long time staring is proposed by using the continuity and inter-frame correlation difference of target and noise signal in multi-frame bearing-time-energy graphs or bearing-time records obtained by long time staring.The sparse difference between target and noise of a single frame bearing-time-energy graph obtained by receiving data matching filtering is used to study the underwater weak target detection method based on the sparse representation of sonar target spatial and temporal scattergram.Finally,the validities of the proposed algorithms are verified by the sea trial data,and the accurate detection and Direction-of-Arrival estimation of distant weak targets can be achieved based on the seabed stationary array.