Research On Target Echo Characteristics In A Plane-parallel Layer Waveguide

Due to the impact of seabed and surface, the echo characteristics of target in shallow water are affected greatly compared with free field. It makes target detection and identification technology facing severe challenges, so the research of target echo characteristics in shallow water waveguide is increasingly widespread concerned. The target echo characteristics in a plane-parallel layer waveguide are studied in this paper.In this thesis, based on the integral formula of Helmholtz and the Kirchhoff approximation, the expression of the scattering sound field in a plane-parallel layer waveguide is derived. Based on this expression, the composition of the target echo in waveguide has been analyzed: the target echoes in a plane-parallel layer waveguide are composed of the echo of direct acoustic wave in free field and the superposition of the scattered waves, which are brought by the equivalent monostatic and bistatic system built up with the source and the image of it on the upper and lower interface. According to this, the formula of the position and amplitude of highlight on smooth and rigid surface, where the monostatic and bistatic sonar in free field, is deduced by use of the steepest descent method. For example, to calculate the echo of ellipsoid targets in a plane-parallel layer waveguide: firstly, determining the highlight position of target in the equivalent monostatic and bistatic system, then calculating the amplitude of highlight; Making the amplitude multiply the corresponding interface reflection coefficient respectively, and then the relative delay time of scattered wave is determined by the highlight position. The nestification of every scattered wave is the echo of ellipsoid targets in a plane-parallel layer waveguide.About the experiments, it aims to analysis the target echo structure and the echo strength, and to verify the correctness of theoretical analysis about waveguide echo. Through dealing with experimental data, it obtains the target echo structure in a plane-parallel layer waveguide, reflects the impact because of the existence of waveguide interfaces. For target echo characteristics of shallow water wave-guide, it provides experimental verification.