Analysis And Research Of Passage Characteristics Of Underwater Sound Targets' Radiated Noise

Analysis on the passage characteristics of ship radiated noise is an important issue in the classification and recognition of ship targets.This paper is concentrated on acquiring targets' passage characteristics from array measured radiated noise and analyzing the information related to targets' properties and sailing status.Versatile methods are applied in the analysis of the real radiated noise to obtain the time-frequency characteristics,passage characteristics of linear spectrum components and the time-change characteristics of multipath channel.Firstly introduced in this paper are the research status of the ship targets' passage characteristics and the related theories,including the components and the typical frequency characteristics of radiated noise,the laws of sound propagation,and the principle of array beamforming.For the cylindrical array used in the test,the beam patterns with signals of different frequencies are obtained by beamforming simulation.The cepstrum theory is introduced,and then the simulation of radiated noise passage characteristics,based on the geometric model of acoustic field and the mathematic form of radiated noise,is run,followed with cepstral analysis.In the verification,the multipath delays acquired from simulative cepstral analysis fit exactly with those expected by the geometric relationship of sound field.Time-delay beamforming is applied to the sea test data to restore the target signal from the array measured radiated noise of different ship kinds,sailing routes and speeds.For each voyage,the time domain passage characteristics and the direction is obtained from the array output signal,and the array gain is calculated.Through the results of beamforming,its effectivity on restoring target signal,strengthening space directivity and raising signal-noise ratio is verified.Using narrow band filter,the passage characteristics of linear spectrum components are extracted,and their power fluctuation near the abeam position is revealed.Of the additive reflection interfering signal,the amplitude fluctuation's factors are analyzed by simulation and theoretical derivation.The fluctuation of the real signal is then determined irrelative to multipath interference.The variation of multipath time delay and the period of target ship's stimulation source are extracted from the real radiated noise by cepstral analysis,accordant with the theoretical expectation.