时变海面复反射系数建模

Modeling of complex reflection coefficient for time-evolving sea surfaces

基于二维时变海面模型和粗糙面电磁散射的低阶小斜率近似方法,研究了海面复反射系数的时变和统计特性.在电磁散射幅度基础上推导了粗糙面反射系数及其相干和非相干分量,相干分量理论计算公式与经验模型一致.仿真结果表明相干分量幅度与经验模型基本吻合,但相位中存在明显的起伏特性,这种起伏在经验公式中没有体现出来.引入Mid-dleton相位差统计模型为反射系数时变特性建模,仿真数据统计与理论分布吻合较好,且概率密度函数的等高图可以很好地表征时变复反射系数间的相关特性.这种吻合性表明复反射系数在短时间尺度上满足高斯分布,但其幅度和频率被海浪长波调制.

Based on the two-dimensional time-varying sea surface model and first-order small slope approximation method,the time-varying and statistical characteristics of complex reflection coefficients from sea surfaces were investigated.In terms of electromagnetic scattering amplitudes,the reflection coefficients and their coherent and incoherent components were derived.The theoretical formula of coherent part is coincident with the empirical model.Simulation results demonstrate that the coherent amplitudes accord with the empirical counterparts,while the phases have unavoidable disturbances,which can not be predicted by empirical formula.Middleton phase difference statistical model was introduced to model the time-varying property of reflection coefficients.The simulated statistics are shown to be in good agreement with the theoretical model,and the contour plots of probability density function can predict the correlation between the complex reflection coefficients adequately.Such agreement suggests that the complex reflection coefficients have a Gaussian distribution on short time scales,but are modulated in amplitude and frequency by the long surface waves.