| The value of research on the Radar scattering properties from dynamic sea surface and ship wakes is very significant in the field of ocean remote sensing and the recognition of ship targets. This dissertation systenmatically presents the research on the Radar scattering properties from dynamic sea surface and ship wakes, and focuses on the modeling of geometry and composite Radar scattering from the ship wakes and its underlying sea surfaces, and the Doppler spectra analysis of the EM echoes from the dynamic sea surface, for both infinite- and finite-depth sea. The main research and work are as follows:1. Based on the theory of facet scattering contribution, the facet scattering model is proposed. This model is suitable for calculating the backscattering coefficient space distribution of two-dimensional sea surface. On the basis of the model, the fast simulation for Synthetic aperture radar (SAR) of the composite model of the two-dimensional linear sea surface and ship Kelvin wake is realized, the influence of the radar and marine environmental parameters such as polarization, ship speed, wind speed, ship structure, wind direction ea al. on SAR simulation is analyzed. This provides a rich template for the training of the SAR image recognition algorithm of ship Kelvin wakes.2. Combine with the introduction of the tapered incident field, the Small Slope Approximation (SSA) is firstly utilized to study the electromagnetic (EM) scattering coefficients and the Doppler spectra charactersitics of backscattered echoes from the two-dimensional dynamic sea surface. The influence of radar and marine environmental parameters such as frequency of the Radar incident wave, polarization, incident angle, wind speed, wind direction et al. and nonlinear effect on the Doppler shift and spectral width is analyzed in detail. Simulation results show that compared with linear sea surface, the nonlinear sea surface is more consistent with the actual marine scene. It is also found that the SSA-2 is capable of elaborating the characteristics of the Doppler shift and spectral width of echoes backscattered from dynamic sea surface for different polarizations. Then, combined with the geometry model of ship internal wake, the EM scattering characteristics from the ship internal wake with low sea states are mainly studied by using regional separation. The influence of the nonlinear effect and ship wake superpositon on the scattering coefficient is analyzed.3. Combining the hydrodynamic theory with the finite-depth sea spectrum and the revised CWM model, we simulate the two-dimensional fetch-and depth-linited nearshore sea surface, and the statistical differences between different fetch- and depth-sea surfaces are compared and analyzed successively. Based on the SSA-2, the EM scattering and Doppler spectra from dynamic surfaces of two-dimensional finite-depth sea are studied, the influences of water depth, the fetch, polarization and other radar and marine environmental parameters on the Doppler spectra are evaluated and analyzed in detail. Simulation results reflect that the nonliear effect is much more intense in bigger fetch-and finite-depth nearshore sea, meanwhile, the discussion also indicates that the nonlinear hydrodynamic effect impacts co-polarization results more obviously than their cross-polarization counterparts.4. First, based on the thin shio theory and the boundary conditions of finite-depth sea, the geometric modeling of the finite-depth ship Kelvin is realized, and the influence of the water depth Froude number on Kelvin wake wave pattern is discussed. Then, combined with facet scattering model, the SAR imaging simulation of the finite-depth ship Kelvin is realized. The influence of the water depth, polarization and other radar and marine environmental parameters on the imaging results is analyzed. Finally, the EM scattering coefficients from the composite model of the finite-depth sea surface and finite-depth ship Kelvin are calculated by using SSA-II model. The influence of the water depth on EM scattering coefficients from the composite model is discussed. And, the Doppler spectra charactersitics of the composite model are investgated. |
