Research Of Electromagnetic Scattering On Finite Depth Sea

The finite depth sea has different characteristics from the traditional infinite depth sea under the influence of the bottom terrain and shallowing effect.It has very important significance in military strategic monitoring and civil technology research.There are the following difficulties in the study of finite depth sea: Different from the traditional infinite depth sea surface,due to the sensitivity of the finite depth sea surface to the influence of water depth factors,the geometric modeling of the finite depth sea surface has been a hot topic at home and abroad.The problem of electromagnetic scattering in finite depth sea is usually a large electrical problem,which is a difficult problem in computational electromagnetics.It is different from the traditional electromagnetic scattering of infinite depth sea surface.The influence of water depth on its electromagnetic scattering cannot be ignored.The problem of bottom topography detection in finite depth sea is of great significance to the scientific management and protection of the ocean.However,how to simulate the entire process of radar imaging from the sea surface to the bottom topography inversion has been lacking in effective methods at home and abroad.The problem of bottom topography detection in finite depths is of great significance to the scientific management and protection of the ocean,but how to simulate the entire process of radar imaging from the sea surface to the bottom terrain inversion is a hot issue at home and abroad.Therefore,in this paper,the research and analysis are performed from the four aspects: geometric modeling of finite depth sea surface,electromagnetic scattering of sea surface,radar imaging,and water depth inversion.The main work of this article consists of four parts:Part 1: Combined with finite depth sea spectrum models and traditional hydrodynamic theory,a linear filtering method was used to establish a geometric model of the surface.By comparing the finite depth sea surface under different water depths and wind speeds,the law of geometric model changes is obtain : First,at the same wind speed,the greater the water depth,the greater the undulations of its surface.Second,at the same water depth,the greater the wind speed,the greater the undulation of the sea surface.This conclusion is consistent with the actual sea surface conditions,which proves the effectiveness of the method.Part 2: Study on the electromagnetic properties of the finite depth sea surface using Physical Optics.The problem of electromagnetic scattering on a finite depth sea surface is usually a large electrical problem.Therefore,the use of Physical Optics in the research process can effectively reduce computer runtime and memory consumption.By comparing with the Multilayer Fast Multipole Algorithm,this paper verifies that the Physical Optics has better accuracy under different water depth conditions,and proves that it can be used for electromagnetic scattering calculations in finite depth sea.In addition,by calculating and studying the scattering characteristics of the finite depth sea surface under different water depths,wind speeds and incident angles,we obtain that at the same incident angle,the difference in scattering coefficient between shallow and deep water will increase with the increase of wind speed.At the same wind speed,when the incident angle is medium,the effect of the water depth factor on the backscattering coefficient increases with the increase of incident angle.Part 3: Radar imaging of finite depth sea surface using surface element method and back projection(BP,Back Propagation)imaging algorithm.Due to the different scattering characteristics of the finite depth sea surface with different water depths,the surface scattering method can be used to calculate the electromagnetic scattering coefficients of the finite depth sea,and then the BP imaging algorithm is used to perform radar imaging on the finite depth sea.In this paper,SAR remote sensing imaging is performed on typical sandy slope terrain,the flood disaster area and the actual Bohai Bay area,and the simulated SAR images with good matching with the actual terrain are obtained.Finally,the response characteristics of the Bohai Bay terrain at different wavebands,incident angles,wind speeds and wind directions were simulated and analyzed.The following conclusions were obtained: Under the conditions of the same angle of incidence,wind speed,and wind direction,the lower the frequency of the radar wave,the better the imaging effect of SAR on the bottom terrain.Other conditions are the same,the smaller the angle of incidence is,the better the SAR imaging effect is.The other conditions are the same,when the wind speed is about 5m/s,the SAR imaging effect is the best.The other conditions are the same,in the wind direction angle range from downwind to crosswind,SAR imaging has good effect.Part 4: Inversion of seafloor topography from radar SAR images.Based on the sea surface SAR remote sensing imaging model of the topography in finite depth sea,a water depth inversion algorithm was developed using some prior terrain data and real SAR images to effectively retrieve the seafloor topography.In this paper,the algorithm is applied to the Bohai Bay area,and the SAR image of this area is used to make an exploratory study on the inversion of the seabed terrain in the Bohai Bay area.The inversion results match well with the actual water depth.