Simulation On The Inversion Of Attenuation Coefficient Of Ocean Sediment With Reflected Sound Field

For the shallow sea environment,the seabed,as the lower boundary of the acoustic wave propagation,plays a very important role.The attenuation coefficient of the sedimentary layer will have a direct impact on the acoustic wave propagation.It is of great significance to effectively obtain the attenuation coefficient of the seabed sedimentary layer for the study of the law of the underwater acoustic propagation and has a broad application prospect.A large number of studies have shown that the attenuation coefficient of the sedimentary layer is a frequency related parameter,which is not sensitive to other seabed parameters.It is difficult for the traditional inversion method to carry out direct inversion calculation.Therefore,this thesis studies the direct inversion method of the attenuation coefficient of the seabed sedimentary layer from the aspect of frequency.Based on the theory of reflected sound field,this thesis studies the direct inversion calculation of the parameters which can indicate the relationship between attenuation coefficient and frequency.The theoretical research and simulation analysis are carried out from the homogeneous liquid semi-infinite seabed and the liquid stratified seabed models respectively.It provides a feasible method to estimate the attenuation coefficient of seabed.This method is simple,novel and easy to calculate.It can be implemented and measured at short range.The specific research content of this thesis is as follows:(1)Considering the seabed sedimentary layer as a uniform fluid,according to different seabed structure models and marine environment,the forward calculation model is given by using the sound reflection theory,and the time-domain waveform prediction method of the reflection signal which only interacts with the seabed is studied.The influence of the attenuation coefficient of the sedimentary layer on the seabed reflection signal and the feasibility of the inversion of the sound source and hydrophone position are mainly studied.(2)This thesis studies the optimization algorithm,compares the basic particle swarm optimization algorithm with the standard differential evolution algorithm,and improves the standard differential evolution algorithm with better optimization performance,and obtains the Niche Differential Evolution Algorithm and the Memetic Differential Evolution Algorithm.The results show that the Memetic Differential Evolution Algorithm has more stable performance and faster convergence speed for solving the optimal value of complex functions.Therefore,the Memetic Differential Evolution Algorithm is selected as the optimization algorithm of parameter inversion method in this thesis.(3)The time domain waveform of the reflected signal is selected as the forward model for the two kinds of seabed models,and the simulation calculation of parameter inversion is carried out.The appropriate cost function is established and the sensitivity and uncertainty analysis are carried out.Compared with the theoretical true value,the average error of simulation inversion is smaller,and the result error can be controlled when there is noise,which effectively proves the feasibility of the inversion method proposed in this paper.