Geoacoustic Parameters Inversion Based On Waveguide Impedance In Acoustic Vector Field

In shallow water environments,the ocean geoacoustics parameters have a huge impact on the transmission of underwater acoustic signals,and thus the research on the parameters acquisition techniques has also been a hot topic in underwater engineering.With the continuous development and perfection of vector sensor's production technology and vector signal processing technology,the application of vector sensor has also become one of the most important researches in the field of underwater acoustic.However,the research on geoacoustic inversion with physical properties in acoustic vector is still relatively rare.In view of this article,to study theoretical modeling and physical characteristics in the shallow water acoustic vector field as the core,explores the energy attenuation laws and spatial distribution characteristics of physical quantities in vector field,as well corresponding physical mechanisms.A number of experimental measurements were carried out to provide strong supports for the above theoretical modeling and analysis of physical laws.The main researches are as follows:Firstly,based on the equation of wave motion,the vector modeling of a Pekeris waveguide in shallow water with elastic bottom has been built using NMM(Normal Mode Method)and FFM(Fast Field Method)respectively.To obtain the modal eigenvalues in NNM,two methods based on Complex Phase Function(CPF),including the path trace method and complex effective depth method,have been compared.The results proved that,the complex effective depth method has higher computational efficiency and accuracy,and is more suitable for used in engineering.Consider the FFM is easy to solve in calculating,based on the potential functions and boundary conditions in each media,the theoretical modeling has been promoted to an ocean environment with sound speed profile or multi-layered elastic bottom.Sceondly,in the study of physical quantities in acoustic vector field,in addition to discuss the regular physical quantities-sound pressure p and velocity v,the other three physical quantities,such as the complex intensity I,the same point cross correlation function p and the waveguide impedance Z,have been analyzed with formula derivation and simulation examples.As the waveguide impedance Z offset the source level and expand the impact of wavefront propagation,and more conducive to the use of its propagation characteristics in the whole of the propagation distance.Its vertical component Zz,due to the effct of vertical velocity(vz),can better embody the acoustic characteristics of ocean bottom.For above reasons,the multi-frequency vertical waveguide impedance Zz(fi)is presented as the inversion model in-dpeth study in this paper.Theoretical analysis and simulation results showed that compared to other physical quantities in acoustic vector field,Zz(fi)with higher sensitivity and better resolution to the parameters in sediment and ocean bottom.It is more suitable to be applied to inversion research for geoacoustic parameters.Thirdly,according to the normal mode method,the distribution characteristics of above vector physical quantities in frequency-range domain have been studied through theoretical analysis and simulated computation.The results show that,including the sound intensity I?the velocity spectrum |v|2?the waveguide impedance Z and the same poiny cross correlation function ?,they all will form stable interference structures in frequency-range domain represented by waveguide invariant ?.However,due to the impact of the non-interference items,the interference structures of above four physical quantities will be suppressed.From the definition formulas of complex intensities in vector field(I),it is obvious that no matter the real part of vertical complex intensity[Re(Iz)]or the imaginary part of horizontal complex intensity[Im(Ir)],they both only contain the interference items in their expressions,their interference structures formed in frequency-range domain will be clearer and ealiser to extract.From the simulation results,although the Re(Iz)and Im(Ir)have some difference in distribution,they both can be described by the waveguide invariant ?.In this dissertation,with a multi-scale line filter based on hessian matrix and measured data from ocean,the conclusion is proofed.Finaly,a tank experiment and an ocean acoustic vector field measurement have been carried out to verify the above research.In the tank experiment,the validity of the scale model utilized in sound propagation is proved by normal mode theory,and a simulation sound propagation experiment has been carried out successfully with elastic bottom,the theoretical modeling was verified by the measured data.Consider the measured data in tank as the measured result by a horizontal array,the F-K transform has been first introduced to obtain the dispersion curves in fluid,and more high order normal modes informations are obtained.In the ocean trials,the ship radiated noise has been used as the broadband source,with the multi-frequency vertical waveguide impedance Zz(fi)from measured data,the geoacoustic parameters have been inversed.Moreover,the interference structures from measured data have verified the inversed results.In addition to above works,a new measurement scheme carried out in a anechoic tank is designed to obtain the compressional-and shear-wave velocity of large elastic material.The scheme based on Snell law in layered medium and traditional transmitting method,and provides a new way to measure the sound velocity in elastic media.