Research On The Applicability Of Using Ocean Bottom Interface Wave For Sea Source Localization

Passive ranging of underwater targets has always been an important aspect in the field of underwater acoustics.Scholte wave,as an interface wave,can propagate long distances along the water-sea floor interface,and its characteristic can provide a possible application prospect for marine target positioning.For this reason,this paper is devoted to the research of passive ranging of underwater targets using geoacoustic signal.In shallow water,artificial explosive source(such as TNT)and ship radiated noise are the main excitation sources of interface waves in sea experiments,which have the advantages of wide frequency range and obvious signal characteristics.Therefore,this paper only focuses on the positioning of these two typical sources.First,the propagation mechanism and modeling method of sound field are researched in three typical environments.In this paper,the three typical environments refer to the Pekeris model with elastic sea floor as well as with uniform elastic layer and non-uniform elastic layers.The Scholte wave dispersion characteristics are analyzed by simulation.In addition,the acoustic vector field characteristics are studied which provide a theoretical basis for localization based on geoacoustic signals.Secondly,an analytical expression of vertical wave impedance(ratio of pressure to vertical particle velocity)about sound source position information is derived in the Pekeris shallow water with elastic bottom.Based on particle filtering(PF)method,the position of the broadband sound source is estimated.Then,based on the principle of matched field processing,the ship targets can be positioned using frequency difference between the peak of the ocean waveguide spectrum and the peak of spectrum of seabed received signal is defined as cost function.The proposed methods for broadband sound source and ship targets are verified by theoretical simulation and experimental data processing.The researching results have been given as following:1.Modeling and characteristics of the sound field in typical environmentThe theoretical models of the sound field are performed for Pekeris model with elastic bottom and with uniform as well as non-uniform elastic layers added to the elastic bottom.In non-uniform elastic layer,when compressional and shear wave velocities are changing with depth,will lead to the coupling of compressional and shear waves.As the coupling effect,a typical sound velocity distribution(where the compression wave velocity has a n2 linear distribution and the square of shear wave velocity has a linear distribution)is derived in detail.The simulation and experimental results show that the eigenvalue of sound field decreases due to the coupling between compressional and shear wave,which has a greater impact on the far-field,and will improve the far-field prediction accuracy.In addition,the excitation and dispersion characteristics of Scholte waves in three typical environments are studied.Finally,the expression of acoustic vector field is derived theoretically.The theoretical and simulation results show that the propagation law of sound pressure and horizontal particle velocity are basically the same,while the propagation law of sound pressure and vertical particle velocity are quite different.The vertical wave impedance obtained by combining the pressure and the vertical velocity fluctuates greatly with distance,and contains more sound field information,which providing a theoretical basis for locating sound sources based on vertical wave impedance.2.Use the geoacoustic signal to locate the explosive sourceAiming at the explosive source,passive positioning studies were performed based on the Scholte wave dispersion characteristics and the vertical wave impedance at ocean bottom interface.Due to dispersion characteristics of Scholte wave,the group velocities at different frequencies are different.The range is estimated by using the group slow speed difference and time difference of Scholte wave at multiple frequencies.This method does not involve the depth information of sound source,it is impossible to estimate the depth of the sound source.The sound source is positioned based on PF algorithm using vertical wave impedance at ocean bottom interface.The measurement equation is constructed using the relationship between vertical wave impedance and the sound source position.Simulation and experiments verify the effectiveness of PF method with vertical wave impedance for the localization of explosive source.In addition,the positioning performances of the pressure and vertical wave impedance as the measurement vector are simulated and analyzed respectively.Simulation results show that the source depth will affect the accuracy of positioning when the measurement vector is pressure.The PF method with vertical wave impedance as measurement vector is not affected by source depth and source spectrum information,making it more tolerant and more robust than that with pressure in positioning.3.Positioning of ship using ship radiated noiseDuring navigating of ships,the frequency corresponding to the peak of the spectrum of ship noise is the result of interaction between ocean waveguide and the source.Based on the principle of MFP(Matched field processing),the frequency difference between the frequency corresponding to the peak of the ocean waveguide spectrum and the peak of the spectrum of the seabed received signals is defined as a cost function.When the cost function takes the minimum value,the depth and range of the ship can be obtained.The effectiveness of the method has been verified by simulation and experimental data processing results.Simulations are performed under typical sound velocity profiles,and the simulation results show that the method can effectively estimate the target range,but multi-value phenomena will appear in the depth estimation.Increasing the selected frequency band can effectively reduce the occurrence of multi-value phenomena.In addition,no matter whether the radiated noise power spectrum is a pure continuous spectrum or a continuous spectrum superposed line spectrum,the simulation results show that the positioning method can effectively estimate the target range.When the radiated noise power spectrum is superposed on the line spectrum,the positioning accuracy of the method is reduced,but the positioning accuracy of the method can be improved by increasing the selected frequency band.