Deep Ocean Acoustic Tomography With Mobile Node

Long-term,large-scale observations of the marine environment are important for understand-ing evolution of the ocean.Ocean acoustic tomography mainly uses the propagation characteristics of acoustic signals to infer the properties of marine media,which is an effective technology to real-ize long-term and large-scale ocean monitoring.The acoustic tomography system combined with mobile nodes and moorings can utilize its abundant spatial sampling to enhance the resolution and decrease the uncertainty of ocean acoustic tomography.Therefore,this thesis uses Hybrid Coordi-nate Ocean Model(HYCOM)simulated South China Sea environmental data to carry out numerical simulation of two-dimensional and three-dimensional deep ocean acoustic tomography with mobile node and moorings combinationFor the ocean acoustic tomography of two-dimensional vertical slice,the thesis proposes a hybrid tomography approach based on matched-field processing and ray travel time tomography Firstly,the adaptive parameterized matched-field tomography is used to overcome the model mis-match problem of traditional matched-field tomography.Under the trans-dimensional Bayesian framework,both the model and environmental parameters are regarded as variables.the posterior probability density distribution of all unknown parameters are obtained efficiently by reverse jump Markov chain Monte Carlo(rjMcMC)algorithm,which achieves joint processing of model selec-tion and parameter estimation.The results of matched-field tomography show that the application of mobile node reduces the uncertainty and error of parameter estimation.Furthermore,the out-put of matched-field tomography is taken as the reference sound speed field of the ray travel time tomography,and the inverse problem is solved by the weighted least squares which exploits the spa-tial correlation characteristics of the sound speed field.The research results show that the hybrid tomography approach can effectively reduce the estimation error of the sound speed field.The three-dimensional ocean acoustic tomography mainly research the mesoscale eddy of South China Sea by the mobile node at the periphery of 160kmx 160km region.Time-varying sound speed field is used to simulate the space-time asynchronous phenomenon caused by mov-ing acoustic tomography,and the tomography output is the mean sound speed field in short dura-tion.Numerical simulations indicate that the three-dimensional acoustic tomography can roughly detect the movement trend of the eddy,and the overall root mean square error of the tomography is within lm/s.Finally,this thesis compares performance of mobile acoustic tomography system with different topologies,and finally proposes a reasonable design scheme of ocean acoustic tomography systems for future sea experiment.The theory and method of this thesis are validated by numerical simulation.The research work of this thesis enriches the ocean acoustic tomography technology:the two-dimensional hybrid tomography approach improves the estimation accuracy of sound speed field;the three-dimensional mobile acoustic tomography study completes the feasibility analysis of tomography in a specific area(South China Sea).