The Simulation Study Of Ocean Ship Wakes Imaging By SAR

Based on theoretic analysis and adopted computer simulation, this thesis has made an in-depth study of the ship wake features, the Synthetic Aperture Radar (SAR) imaging mechanism of wakes, the simulation of SAR imaging of wakes, the optimal observing conditions of SAR and other related problems. It is the fundamental research work of ship wakes detection and of ship's moving parameters inversion.At first, the generating mechanisms of four kinds of wake features are studied in the thesis. We have simulated the features of ocean surface waves, Kelvin wake, narrow V wake, turbulent wake, vortex wake, and internal wake. The kinetic equation of Kelvin wake have been analyzed and improved, which can be used to calculate the Kelvin wake of a submerged moving body.We studied radar backscattering models of ocean surface and modulation mechanism of SAR signal. And the research focuses on the composite surface backscattering model and velocity bunching modulation mechanics. Based on these theories, we built up an SAR imaging model pertained to ocean waves. This imaging model includes three characteristics. First, three-scale model have been utilized for calculating microwave backscattering from ocean surface. The imaging model takes into account the intermediate waves, which modulate the short waves in addition, to make up the limitation of two-scale model. Second, the imaging model built here has taken into account the tilt modulation, the hydrodynamic modulation, and current modulations of radar cross section. Consequently, it has realized the imaging simulation of four kinds of wakes with the same imaging model. Third, the orbital velocity of ocean wave was considered as the basic dynamic factor, and the imaging model calculates the influence on raw data by the wave movement according to the orbital velocity.This thesis has studied the SAR raw signal simulator scheme of distribute targets. By comparing of the theories and designs of in existence simulators and combining of the simulated SAR raw data of ocean surface, we improved the former scheme of distributetargets simulator. The new scheme is more flexible than the old one.Through the analysis of the simulated SAR images for different SAR system parameters, observing conditions, ships' types and motion parameters, as well as sea state parameters, the thesis has studied the optimal observing conditions for different kind of wakes and probed into the problem of motion parameters inversion and wake detection.This thesis has studied the wake features and generated SAR raw signal which including wakes information, after which we understand substantially the generating mechanics of ship wakes and its SAR imaging mechanism. This work has established the theoretical foundation for improving SAR imaging quality and increasing detection probability of ship wakes.