| Due to the innovation of submarine technology,acoustic stealth technology and underwater acoustic countermeasure technology,the detection performance of monostatic sonar system for low-noise targets is difficult to meet the operational needs,while the comprehensive detection of multistatic system may greatly improve the detection performance,which provides a new way to solve the detection problem of quiet targets.However,when the multistatic sonar system works,there is strong interference of direct wave,and the energy of target echo is smaller than that of direct wave.When the receiving base estimates the direction of arrival,the target echo will sometimes be submerged by the direct wave interference,which causes difficulty for subsequent target detection.Designing the transmitting waveform and spatial filtering at the receiving end are two effective methods to suppress the direct wave interference.The vector hydrophone can simultaneously measure the sound pressure and vibration velocity information at a certain point in space,which has more advantages than the traditional sound pressure hydrophone.Therefore,applying the vector hydrophone array to the receiving base can obtain better direct wave suppression effect.Firstly,this paper introduces the key technologies of bistatic and multistatic sonar system,and studies the basic principle of hydrophone array signal processing.Secondly,the detection performance of monostatic sonar based on unit average CFAR detection is theoretically deduced,and the variation law of monostatic sonar detection probability with detection distance is modeled,which are "ideal model","exponential model" and "Fermi model",respectively.Based on the cumulative detection probability,four systems are compared,which are monostatic distributed,monostatic centralized,multistatic distributed and multistatic centralized sonar systems,and it is quantitatively analyzed by the detection range in which the detection probability of sonar system is above the detection threshold.Among them,the monostatic distributed performance is the worst and the multistatic centralized performance is the best,but its false alarm level is the highest.The false alarm levels of multistatic distributed and monostatic centralized are close,and the multistatic distributed performance is better,which is the best working mode of sonar system.On this basis,the detection range of doublelayer multistatic sonar system is quantitatively analyzed by using the "exponential model" monostatic detection probability curve and multistatic distributed working mode.Thirdly,aiming at the direct wave interference in multistatic sonar system,this paper analyzes and simulates the direct wave suppression technology based on transmit waveform design and spatial filtering technology.On the one hand,optical orthogonal codes(OOC)are used to encode the transmitted waveform,and its autocorrelation characteristics are used to separate the direct wave from the target echo at the receiving end;On the other hand,the direct wave suppression methods of adaptive beamforming technology based on spatial smooth vector array MVDR and spatial matrix pre-filtering technology based on second-order cone programming are studied theoretically,and the simulation results are given.The results show that after spatial filtering,MVDR and MUSIC algorithms can successfully estimate the DOA of target echo.Finally,an experiment on lake is done to verify the effectiveness of spatial filtering algorithm. |
