| With the continuous improvement of comprehensive national strength,the focus of my country’s development strategy has gradually shifted from the inland to the ocean.The rational development and utilization of the ocean is conducive to my country’s comprehensive and sustainable development.Therefore,the study of the ocean is particularly important.So far,acoustic signals are the most effective means of propagation in seawater known so far.Compared with light waves and electromagnetic waves,which propagate better in the air,the propagation of sound waves in water is much less attenuated than them.Shallow sea is the main place for human production and life,so the research on the propagation characteristics of sound field in the shallow sea environment is of great significance for human beings to understand the ocean,utilize the ocean,and develop the ocean.In the study of the propagation of sound field in the ocean,the propagation of sound field from the ocean environment and the seabed plays a role together.Since the end of World War II,many scholars have found that the impact of the seabed on the sound field propagation in the shallow sea environment is much greater than that in the marine environment.Therefore,when studying the characteristics of the sound field propagation in the shallow sea environment,the impact of the seabed on the sound field propagation should be considered.Research on the seabed is mainly to obtain the geoacoustic parameters of the seafloor,including the transverse and longitudinal wave sound velocity and density of the sedimentary layer,and the transverse and longitudinal wave sound velocity,density and sound velocity attenuation of the seabed.In this paper,focusing on the inversion of geoacoustic parameters in shallow seas,a nonlinear Bayesian inversion method based on normal wave group velocity is studied for the inversion of sedimentary layer thickness,density and longitudinal wave sound velocity,seabed density,transverse wave sound velocity and longitudinal wave sound velocity.Firstly,according to the propagation properties of normal waves in the shallow sea,a Pekeris waveguide forward modeling model with liquid sedimentary layers is established,and the model group velocity dispersion curve is deduced and calculated by using the n-layer submarine medium group velocity dispersion theory.The calculation results of the sound field software are compared,which verifies the correctness of the forward modeling model.Secondly,the optimization algorithm is discussed,the shortcomings of the traditional optimization algorithm are analyzed,and an adaptive simplex simulated annealing based on the nonlinear Bayesian algorithm is proposed(Adaptive Simplex Simulation Annealing,ASSA)for inversion;then based on the likelihood function to establish the objective function between the actual group velocity and the theoretical group velocity and analyze its sensitivity to the inversion parameters;on the basis of the above work,establish the parameterization The marine environment model is used to invert the simulation data,and the posterior probability density of the geoacoustic parameters to be inverted is obtained as the inversion result based on the Metropolis acceptance criterion.The results show that the posterior probability density of each parameter is basically consistent with the parameter sensitivity.,the inversion results are also close to the set simulation parameters,which proves the feasibility of the inversion method.Finally,combined with the sea test data,extract the acoustic wave group velocity dispersion information for nonlinear Bayesian inversion,analyze the inversion obtained geoacoustic parameters,discuss the relationship between the parameters,and write the inversion obtained geoacoustic parameters into the KrakenC sound field software The calculation of the group velocity dispersion curve and the comparison with the group velocity dispersion curve extracted from the experimental data verify the practicability of the inversion method. |
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