Microwave Scattering from a Ship on a Sea Surface: Incoherent Matrix and Coherent Intensity Computed from Single and Double Bouncing PO and MoM-EPILE

Scattering from a deterministic object in the presence of a randomly rough surface, such as a ship on a sea surface, can be characterized by statistical moments. Full-wave methods, such as the method of moments (MoM), provide accurate results but can be time-consuming. To account for both the gravity and capillary waves, a full sea spectrum is used, which constrains the consideration of a one-dimensional sea surface to include all roughness scales. Asymptotic methods are a good compromise between the computation time and accuracy of the results. In this study, the field scattered by a trapezoidal ship on a 1D sea surface is calculated by iterating the physical optics approximation and incorporating evanescent waves. In addition, the resulting closed-form expressions allow us to derive the associated coherent components analytically by considering a finite and infinite sea surface length. They are validated by comparison to the MoM combined with the extended propagation-insidelayer-expansion (EPILE) method, which can separate bounce orders. The results of the incoherent components, evaluated using a Monte Carlo process, are also shown by introducing a novel concept, based on the centered inter-correlation matrix between the single and double bounces, to quantify the different incoherent contributions. This concept highlights the ``backscattering enhancement'' phenomenon, only observed for a single rough surface with high slopes.