Study On Angular Composite Facet Model For Electromagnetic Scattering From Sea Surface And Ship Wake

In view of finer resolution of radar systems and the increasing demand for real-time monitoring of the sea surface in the military and civilian fields,the focus of research on electromagnetic(EM)scattering from the sea surface has shifted to studies on EM scattering from the sea surface under the influence of multiple factors,such as studies on sea surface with ship wake and on sea surface with targets on it and on other complex sea scene.Due to the complex structure and real-time variability of the sea surface,the simulation of EM scattering from sea surface and sea surface with ship wake has the following difficulties:First,it is necessary to figure out how to establish a more accurate sea surface and ship wake,so that it can better describe the fine structure of the sea surface and it can make the superpositions of the wake and the sea surface more reasonable as well.Second,it is also necessary to figure out how to establish an accurate facet-based model for EM scattering to meet the increasingly precise requirements of remote sensing on the sea surface,so that it can give out the scattering contribution of every single facet and improve the accuracy of the evaluation.Finally,considering the influence of the ship wake on the fluctuation of the sea surface,how to quantify the impact of the volume scattering of the large amount of foams in the turbulent wake on the scattering from the sea surface and wake is significant.Therefore,this paper systematically studies the angular composite facet model for the scattering from the sea surface and ship wake,and analyzes the scattering from different sea scenes.First,the two typical methods of geometric modeling of the sea surface using the theory of sea spectrum——Monte Carlo for the generation of linear sea surfaces and Creamer model for the generation of nonlinear sea surfaces were described and the characteristics of sea surfaces generated by the two methods were analyzed and it was found that the nonlinear sea surface has more detailed features.Based on the formation mechanism of Kelvin wake and turbulent wake,the morphology of these two wakes was described through simulations and it was found that the Kelvin wake was gradually overwhelmed by the sea surface noise as the wind speed increased,while the turbulent foam wake only attenuated.Second,based on the division of scattering regions and the idea of presenting scattering contribution from each facet on the sea surface,an angular composite facet model(ACFM)with shadowing treatment was proposed.It can give out the scattering contribution of each individual facet on the sea surface and as part of the algorithm,the electromagnetic shadowing algorithm can address the shadowing effects on the sea surface in a geometric manner and analyze the self-shadowing and mutual shadowing separately.The scattering mechanism of sea surface was analyzed using this model and the effects of frequency,angle,wind speed and shadowing factors on the backscattering from a two-dimensional sea surface were discussed.The results show that the mutual shadowing effect is more significant than the self-shadowing effect and cannot be ignored at large incident angles.The simulation results of ACFM agree well with the measurements,so the model is effective and practicable.Finally,combined the theory of radiation transport(VRT),Mie theory and ACFM algorithm the scattering characteristics of the foam-covered sea surface were analyzed with the reflectivity of the foam layer and foam coverage of the sea surface,and the comparison with the measured data verified the effectiveness of the foam-covered sea surface model.Kelvin wakes superposed on the sea surface were analyzed using ACFM,and then the scattering characteristics of the turbulent wake was tentatively studied.The results show that scattering from the foam layer has an enhancement effect on the total scattering of sea surface and turbulent wake.