Study On Electromagnetic Scattering Of Ship Wakes And Its Application

With the development of stealth technology and complex sea conditions,it is more and more difficult to detect and track the ship itself.Ship wake has the characteristics of large scale and long time,and it will not be eliminated in a short time under various sea conditions.Its echo characteristics such as visible light,infrared and synthetic aperture radar(SAR)can be used as a good signal source for detection,which can make up for the limitations of detection and recognition of the ship itself.The detection of the shape or characteristic signal of the ship wake can not only obtain the important information of the ship's draft,speed,etc.,but also distinguish the ship type and navigation state,so as to indirectly identify the moving ship itself.Therefore,the research of ship wake has important application value and academic significance in marine target detection,national defense security and other aspects.In this thesis,focusing on the target of ship wake,the shape and composition characteristics of Kelvin wake and turbulent wake are analyzed by establishing geometric model.Then,the electromagnetic scattering models of ship Kelvin wake and turbulent wake are established by using physical optics method(PO),semi-deterministic facet scattering model(SDFSM),vector radiative transfer theory(VRT)and Mie theory,respectively,and the relevant dispersion is obtained radiation characteristic parameters.On this basis,considering the characteristics of wake,which is an electrically large target,using the basic principle of SAR imaging,and combining GPU parallel acceleration technology to improve the efficiency of calculation,the SAR simulation imaging of wake is realized,which makes the research more practical.The main work of this thesis is as follows:1.The formation mechanism of Kelvin wake and turbulent wake and their fast geometric modeling method are studied.Using Elfouhaily sea spectrum and Longuet Higgins directional distribution function,a wind driven sea surface model is established.Considering the co-existence of wake and rough sea surface,a method of intensity fitting and superposition is proposed to effectively establish the three-dimensional geometry model of wake-sea surface composite.2.The electromagnetic scattering model of Kelvin arm is established by using periodic surface scattering method.The scattering coefficient formula of periodic rough sea surface at any incident angle is derived in detail.By improving the finite periodic surface scattering cross-section formula,the infinite periodic surface scattering cross-section formula is approximated,and the infinite period surface and finite-long periodic surface scattering problems are unified under certain conditions.Considering the obvious periodic structure of Kelvin wake,especially in the Kelvin arm region,the scattering cross section of Kelvin arm region is simulated by using the periodic surface scattering algorithm,and the influence of different ship speed,hull size and incident parameters on the scattering intensity distribution of the wake is analyzed.3.The electromagnetic scattering model of turbulence wake is established.Based on the Mie theory,the scattering problems of single layer and double-layer spherical particles are studied respectively.The radiative vector transport theory(VRT)is used to study the composite scattering characteristics of the bubbles in the wake.The scattering coefficients of the turbulent wake are calculated by using the particle size distribution of the wake bubbles obtained from the known experiments,and the electromagnetic scattering simulation of the turbulent wake is realized.4.The parallel acceleration calculation of electromagnetic scattering from the electrically large sea surface with wake is realized.Considering that the sea area with wake has the characteristics of large scale,in order to improve the calculation efficiency,combined with the characteristics of semi-deterministic surface element scattering model algorithm,the algorithm is optimized by using the asynchronous transmission,shared memory and other optimization technologies in GPU-CUDA parallel acceleration technology,and the optimization algorithm of SAR imaging simulation of wake sea area is realized.