Research On The SAR Imaging And The Estimation Of Ship Parameters About Kelvin Wake

The study on the Synthetic Aperture Radar(SAR)imaging of ship wakes and estimation of ship parameters are playing a significance role in the ship detection under marine environment.Especially with the rapid development of stealth technology,it is becoming more and more difficult to classify and recognize ship targets directly from SAR images.In order to achieve higher accuracy in the ship targets detection,wake features of SAR images could be utilized to estimate the ship parameters.As a kind of ship wake,Kelvin wake normally shows clear texture features in SAR images,and it has different electromagnetic scattering and imaging characteristics under different conditions.Therefore,using Kelvin wake to detect ship targets and retrieve parameters of ship motion is an important method.In this paper,a systematic research,concerning the SAR imaging of Kelvin wake and the estimation of ship parameters,has been implemented.In addition,the geometric modeling,electromagnetic scattering modeling as well as the SAR image simulation have also been carried out for the sea surface and the Kelvin wake.The main work of this paper includes: 1.Based on the wave spectrum model and Longuet-Higgins directional function,the two-dimensional linear sea surface was simulated by linear filtering method,and the CWM model was utilized to simulate the non-linear sea surface.Compared with the linear sea surface,the influence of non-linear characteristics on the geometric model of sea surface was discussed.Then,according to the point source perturbation theory,the geometric model of Kelvin wake was built and superimposed linearly on the sea surface.As a result,the Kelvin wake under the ocean background was obtained.On this basis,the effects of wind speed and ship speed on the geometric structure of sea surface and Kelvin wake were also analyzed.2.Based on the idea of surface panel scattering and the theory of composite surface scattering,a semi-deterministic facet scattering model,which is suitable for calculating the electromagnetic scattering of large-scale sea surface,was established by means of the first-order perturbation model and Kirchhoff approximation model.What is more,the panel scattering distribution of sea surface and Kelvin wake was simulated using this model,and the tilt modulation effect of wake on the sea wave was analyzed in detail.Besides,concerning the non-linear characteristics of the sea surface,the electromagnetic scattering coefficients of the non-linear sea surface were calculated using the second-order small slope approximation model,and the influence of the wake on the electromagnetic scattering coefficients of single and double station for the sea surface were analyzed based on the proposed model.3.Based on the hydrodynamic model of sea surface,three modulation mechanisms of sea wave towards radar scattering echo were compared and analyzed,including tilt,hydrodynamic and velocity spotlight modulation.Furthermore,integrated with semi-deterministic panel scattering model,the SAR imaging simulation model of sea surface was established,and the SAR image simulation of Kelvin wake was implemented based on this model.The effects of radar parameters,sea surface environment parameters and ship motion parameters on the simulation results were discussed,which indicates the optimum observation conditions of synthetic aperture radar for Kelvin wake.4.Based on the local Radon transform,the linear wake detection was realized.And the matching methods,including range matching test method and direction matching test method between ship and wake,were considered.The direction matching test method can not only eliminate the false wake,but also tell the approximate type of wake to a certain extent.Besides,based on the mechanism of Kelvin wake,a two-dimensional estimation method of ship parameters was proposed.Combined with this method,the estimation of ship parameters was studied in the case of removing sea background noise from SAR images based on Markov process.The effects of certain parameters on the estimation results were analyzed,including radar parameters,sea surface environmental and ship motion parameters.Finally,the accuracy and stability of this proposed method was verified compared with the traditional methods.