Research On High-frequency Methods For The Simulation Of Composite Scattering From Three-dimensional Ocean Surface With Targets

Research on electromagnetic scattering from ocean surface is of great significance in applications of microwave remote sensing. For the scattering simulation only from ocean surface, existing methods perform well. However, for the more challenging scattering simulation of ocean surface with targets, i.e. composite scattering simulation, these methods seem much less effective owing to their heavy computational load, enormous memory requirement and other limiting factors. To simulate the composite scattering efficiently, this thesis centers on high-frequency methods and will introduce one hybrid high-frequency method based on ray-tracing.Firstly, the state-of-the-art of the research on ocean surface scattering, especially those popular methods for scattering simulation, has been investigated detailedly. After comparing these methods in terms of both computational efficiency and memory requirement, it is found that high-frequency methods are able to meet the challenging demand of composite scattering simulation. Based on those reported works, this thesis has developed one hybrid high-frequency method named GO+PO+PTD, which is based on ray tracing,and has combined Geometric Optics(GO), Physical Optics(PO) and Physical Theory of Diffraction(PTD) skillfully to calculate the coupled electromagnetic field, specular scattering and diffraction respectively. When compared with the well-known Shooting and Bouncing Rays(SBR) method, GO+PO+PTD surpasses SBR with better computational accuracy.Secondly, when simulating the curved concave targets represented by flat facets, the computational accuracy of GO+PO+PTD will deteriorate remarkably due to the loss of divergence factor(DF). To remedy this loss, a simple and effective factor, entitled Virtual Divergence Factor(VDF), has been proposed to play the role of DF. It is found that VDF can greatly improve the simulation accuracy of GO+PO+PTD for curved concave targets.Moreover, the highly effective kd-tree, the best accelerating structure on the whole, has been implemented to speed up the ray tracing.Lastly, the good accuracy, great flexibility and excellent efficiency of GO+PO+PTD with VDF’s remedy and kd-tree’s acceleration has been fully demonstrated by many typical testing cases, which include ships, a generic missile, a helicopter, the ”COBRA”cavity and the ocean surfaces with or without targets. Moreover, to further show its enormous potential, an extremely complex and electrically large model, including a large transport ship, a helicopter and the ocean surface, has been successfully simulated by GO+PO+PTD. Considering that this composite model is the most complex and realistic one among those reported, the above work, especially the GO+PO+PTD with VDF and kd-tree, should be able to advance, to some extent, the research on electromagnetic scattering from ocean surface.