Acoustic plane-wave reflection from a rough surface over a random fluid half-space

Plane-wave reflection from a rough surface overlying a fluid half-space, with a sound speed distribution subject to a small and random perturbation, is considered. A theory based upon a boundary perturbation method in conjunction with a formulation derived from Green's function for the coherent field in the random medium have been applied to a typical oceanic environment to study their effects on the plane-wave reflection. By considering the coherent field itself, the plane-wave reflection may be obtained straightforwardly through a procedure consistent with the formalisms currently employed in rough surface scattering. The results show that both the rough surface and medium inhomogenieties may reduce the plane-wave reflection, however, the characteristics of the curves representing their effects are different, enabling us to identify the dominant scattering mechanism. The results for the coherent reflection due to the individual scattering mechanism are compatible with those found in the existing literature.     

Acoustic plane-wave scattering from a rough interface over an inhomogeneous transition fluid layer

Acoustic scattering of a plane wave incident upon a rough surface over a transition fluid layer within which both the density and sound speed vary with depth is considered. A theory based upon a boundary perturbation method has been applied to a typical seabed environment to study the power spectral density representing the energy distribution of the scattered field over the space. The effects of frequency and roughness properties, including the roughness height, spatial correlation, and power spectrum, on the power spectral density have been investigated. The results demonstrate that the power spectral density of the scattered field depends upon all the aforementioned parameters, particularly the correlation length and the power spectrum of the rough surface, a conclusion in distinct contrast to the results for the coherent field obtained in an earlier study. It was found that the constituents of the rough surface such as the correlation length and wavenumber spectrum dominate the angular distribution of the scattered energy. These results indicate that it is crucial to employ a suitable topological model in the study of rough seabed scattering.     

Acoustic wave scattering from a rough seabed over a sediment layer with generalized-exponential density and inverse-square sound speed profiles

This paper considers acoustic plane wave scattering from a rough seabed on a transition sediment layer overlying an elastic sea basement. The transition sediment layer is assumed to be fluid-like, with density and sound speed distributions behaving as generalized-exponential and inverse-square functions, respectively. This specific class of density and sound speed profiles deserves special attentions not only because it is geologically realistic, but also renders analytical solutions to the Helmholtz equation, making it particularly useful in the study of ocean and seabed acoustics. Based upon a boundary perturbation approach, the computational algorithm for the spatial spectrum in terms of the power spectral density of the scattered field has been developed and implemented. The results have shown that, while the coherent field mainly depends upon the gross structure of the seabed roughness, e.g., RMS roughness, the scattered field is significantly affected by the details of the roughness distributions specialized by the roughness power spectrum and the spatial correlation length of the rough surface. The dependence of the power spectral density of the scattered field on the various types of sediment stratifications, including the constant and the k²-linear sound speed distributions, is also included in the analysis.     

基于微扰法的改进一维分形模型分层海面电磁散射研究

运用微扰法研究了平面波入射分层介质粗糙面的电磁散射,采用改进的一维分形海面模型模拟实际的分层海面,推导出了平面波入射时的散射系数计算公式。通过数值计算得到了HH极化双站散射系数随散射角的变化曲线,讨论了中间介质介电常数和厚度、摩擦风速和入射波频率对双站散射系数的影响,得到改进的一维分形分层海面散射系数的基本特征、分区特征和随频率变化的特征,结果表明散射系数近似具有"量子化"特征。这些结果在诸如海洋遥感、无线电传播与通信、粗糙面重构等方面中有着广泛的应用。