Modeling And Simulation Of Scattering From A Target To Surface Noise In A Shallow-water Waveguide

Compared with the free field, the seabed and surface have large influence onpropagation of acoustic wave, also make the scattering characteristics of the target changelargely in a shallow-water waveguide. In the traditional underwater acoustic detection field,environmental noise is considered to be a distraction, while ambient noise is regarded asuseful information when using underwater noise for target detection. This dissertationpresents a thorough and systematic study on the target scattering modeling and simulationwhich regards the surface noise source as excitation source in the shallow-waterplane-parallel layer waveguide.Paper researches on composition and characteristics of the ocean ambient noise firstly,points out that the noise from sea surface should be considered as useful acoustic source inthe noise detection system, on this basis abstracts the sea surface noise source to be monopolesources located on a certain depth below sea surface, thereby builds the surface noise sourcemodel. Then based on surface noise source model, paper builds the waveguide noise sourcemodel combined with virtual source theory in shallow water. Lastly, using classical targetscattering theory and Green’s function expansions in spherical coordinates, combining withsoft and hard boundary conditions of the spherical target, the paper deduces noise covarianceexpression with spherical target which exists in shallow water waveguide noise source model.The paper has simulated the spherical target scattering directional diagram, visibilitydiagram under the excitation of surface noise and analyzed the simulation results. Meanwhilethe coherence of scattering noise azimuth has been simulated and analyzed. The simulationresults provide a basis for design of noise detection sonar. In the end, paper introduces a tankexperiment. The results of experiment and simulation are in agreement on the trend, partlyverifying the correctness of the model.