Research On Reverberation Suppression Method Based On Spatial Characteristics Of Reverberation Field

Seafloor reverberation is one of the important factors limiting the detection performance of active sonar system under the shallow water environment.Unlike the noise,reverberation is accompanied by the transmitting signal of the active sonar.Its statistical characteristic is non-statistical.And it is difficult to distinguish with the mixing target signals in most cases.So it becomes the subject of attention of many scholars that how to find an effective method to suppress reverberation,to enhance the receiving signal-to-reverberation-ratio.This paper is started with the numerical simulation method of seafloor reverberation,researched on spatial characteristics of the seafloor reverberation field,proposed the signal processing method to improve the signal-to-reverberation ratio,using the spatial correlation characteristics of reverberation.It achieves the purpose of detecting the target echo signal under the reverberation background.Numerical simulation of seafloor reverberation is the basis of the theoretical analysis of reverberation characteristics.Unit scattering model of the reverberation can be used to simulating study the spatial characteristics of the reverberation.The classic scattering unit models equality divided scattering unit using the scales of the seafloor scattering coefficient spatial correlation radius.Phase of the complex scattering coefficients of scattering units obey 0-2π even distributed.And amplitude of the complex scattering coefficients of the scattering units obeys Gauss distribution.In this paper,some improvements of the classical scattering unit model are made as follows.The scattering units are random non-uniform divided,considering random non-uniformity of the seafloor nature.The phase of scattering units complex scattering coefficient is uniformly distributed within the limited range,considering highly random fluctuation of seafloor is limited relative to the acoustic wavelength.The amplitude of scattering units complex scattering coefficient is random and spatial continuous distribution learning the concept of wave height spectrum,considering the amplitude of seafloor scattering coefficient is spatial continuity and randomness.Spatial correlation coefficient and spatial correlation radius of the reverberation are calculated through correlation analysis on different spatial locations of seafloor reverberation.Correlation analysis of simulation seafloor reverberation under different environmental parameters showed that.With the increase of undulating seafloor,the seafloor reverberation spatial correlation coefficient decreases,and the corresponding spatial correlation radius also decreases.With the decrease of undulating seafloor,the seafloor reverberation spatial correlation coefficient increases,and the corresponding spatial correlation radius also increases.The results also proved this conclusion which reverberation experiments of the three interfaces the sand,coarse sand and stones in the experimental tank.’Instantaneous frequency’ is the derivative of the phase function with respect to variable t at some time,which describes the temporal variation characteristics of the signal at that time.Analogy of the concept,we define ’local wave vector’ which is the derivative of the phase function with respect to space variables at some location in the wave field,which describes the spatial propagation characteristics of the position in the sound field.It can be obtained through analysis of local wave vector in the sound field.Local wave vector vectors in the traveling field point at the direction of propagation of the traveling wave.And its modulus is a constant value.But propagation direction of local wave vectors in the reverberation field is not fixed.And its modulus is not a constant value.The traveling wave field can be judged whether or not using the characteristics of local wave vector in the acoustic field.Target echo can be judged whether or not in the time domain,using the variance sequence of the local wave vector,if time series of the local wave vector is statistical analyzed.That constitutes the variance detector of the local wave vector.Simulation results show that.Local wave vector detection performance variance detector is superior to the traditional maximum likelihood detector quadrature receiver.The results of experimental data in the tank show that.We can effectively determine whether the presence of the traveling wave field by calculating the local wave vector in the acoustic field.Variance detector of the local wave vector can be used to detect the target echo signal under strong reverberation conditions.The target echo signal and interface reverberation signal theoretical analysis and numerical simulation and experimental results show that the tank.The space correlation radius of target echo is greater than the space correlation radius of the reverberation,especially in the vertical direction of the target echo vectors.’Perturbation Repetitive Pulse Superposition Method’ enhances the signal-to-reverberation ratio of the received signal using the difference of the spatial characteristics between target echo and reverberation.The transmitter repeatedly transmits a probe pulse to the target,while hydrophone is perturbation in the spatial position.Perturbation amplitude is less than the correlation radius of the target echo,greater than the correlation radius the reverberation.So that positive correlation coefficient of the target echo is larger,but correlation coefficient of the reverberation is smaller and symbols are uncertain after every disturbance.The received signals of multiple perturbations were superimposed.So the associated portion(target echo component in the receiving signal)is enhanced and the relevant part(reverberation component in the receiving signal)is offset.That achieved the purposes of enhancing the target echo and reducing the reverberation.’Perturbation Repetitive Pulse Superposition Method’ can enhance the signal-to-reverberation ratio of target echo by the procession of experimental data in the tank.