ABSTRACT

Subsurface profile is one of the crucial parameters to construct an accurate scattering model of multilayer media. Due to the difficulties of tracing the subsurface profile, the subsurface is often assumed to be flat to simplify the scattering model. The validity of this flat subsurface approximation, however, was examined only by empirical data, and its applicable condition was barely provided in the literatures. The accuracy of multilayer scattering model can be significantly affected without a proper applicable condition. In this paper, two models are investigated: a three-layer media with a rough subsurface (exact geometry model) and a three-layer media with a flat subsurface (approximate geometry model). The scattered fields of these two models are solved by using the Method of Moment combined with the Kirchhoff Approximation. The results indicate that the fields are strongly dependent on the parameters of the roughness of surfaces, the mean thickness of medium, and the angle of incidence. These parameters are assigned with different values to quantitatively evaluate their impacts on the difference in bistatic and backscattering scattering coefficients between the approximate and exact geometry models. Finally, the applicable conditions of the flat subsurface approximation are determined by limiting this difference within 1 dB.

摘要

次表面剖面是构建多层介质精确散射模型的关键参数之一。由于跟踪次表面轮廓的困难，通常假设次表面是平坦的以简化散射模型。然而，这种平坦的地下近似的有效性仅通过经验数据进行了检验，文献中几乎没有提供其适用条件。如果没有适当的适用条件，多层散射模型的准确性会受到很大影响。在本文中，研究了两种模型：具有粗糙地下的三层介质（精确几何模型）和具有平坦地下的三层介质（近似几何模型）。采用矩量法结合基尔霍夫近似求解这两个模型的散射场。结果表明，场强烈依赖于表面粗糙度、介质平均厚度和入射角等参数。这些参数被分配了不同的值，以定量评估它们对近似和精确几何模型之间双基地和后向散射系数差异的影响。最后，通过将此差异限制在 1 dB 以内来确定平面次表面近似的适用条件。这些参数被分配了不同的值，以定量评估它们对近似和精确几何模型之间双基地和后向散射系数差异的影响。最后，通过将此差异限制在 1 dB 以内来确定平面次表面近似的适用条件。这些参数被分配了不同的值，以定量评估它们对近似和精确几何模型之间双基地和后向散射系数差异的影响。最后，通过将此差异限制在 1 dB 以内来确定平面次表面近似的适用条件。