高海况条件下非线性海面与破碎波复合电磁散射特性研究

According to the requirement background of marine monitoring and radar target recognition, this project mainly focuses on the study of composite electromagnetic scattering of nonlinear sea surface and breaking waves in high sea state. Based on the breaking waves spectrum of nonlinear sea surface, the strong nonlinear interaction of the sea spectrum components and the wave breaking process are related. Then a reliable three dimensional dynamic geometric model of the nonlinear breaking sea surface is established for high sea state. On the basis of hybrid algorithm, the electromagnetic scattering polarization features of nonlinear sea surface are analyzed with improved second-order small-slope approximation. The novel multilevel fast multipole algorithm is used to evaluate the scattering field of the complex fine breaking waves. The domain decomposition and irregular mesh generation methods optimize the numerical calculation methods of the coupling scattering field. Finally the model of multiscale full-polarization composite scattering from the nonlinear sea surface and breaking waves in high sea state is established, of which the accuracy and applicability are verified by the measurements. Based on the principle of the quasi-stationary algorithm, the optimum statistical distribution model is established for the sea clutter in high sea state. Considering the volume scattering effect of breaking waves, the comparative analysis of the relativity between the high-resolved Doppler spectrum and spatial distribution pattern of breaking waves is discussed. In view of the electromagnetic scattering mechanism, the internal relations of the breaking sea surface and sea spike are elucidated. This project provides essential theoretical basis for the marine microwave remote sensing technology.

针对海洋监测和雷达目标识别技术的需求背景，本项目重点开展高海况条件下非线性海面与破碎波复合电磁散射特性研究。推导非线性海面破碎波谱，分析海谱分量之间强非线性作用与波浪破碎相互联系，构造可靠的高海况条件下三维动态非线性破碎海面复合几何模型；根据高低频混合电磁散射算法，采用改进的二阶小斜率近似法分析非线性海面电磁散射极化特征，运用新型多层快速多极子法数值计算破碎波复杂精细结构散射场，结合区域分解和不规则网格剖分技术优化耦合散射场数值计算方法，实现高海况条件下非线性海面与破碎波多尺度全极化复合电磁散射建模，结合实测数据验证模型精度和适用性；基于准静态近似原则，进行高海况条件下仿真海杂波统计分布最优建模，结合破碎波体散射效应比较分析高分辨多普勒谱与波浪破碎空间分布模式之间相关性，从电磁散射机理角度阐明海浪非线性特征和破碎波与海尖峰现象的内在联系，为我国海洋微波遥感技术提供必要理论依据。

复杂海况环境下海面电磁散射特性研究是海洋电磁环境建模的理论基础，对海洋监测与海上雷达目标识别等海洋遥感领域相关应用具有重要意义。本项目针对非线性海面与破碎波复合电磁散射机理进行研究，取得以下成果。.1. 建立了破碎波与非线性海面复合几何模型。引入高阶非线性项来表征海谱频率分量之间相互作用，通过合理地选择海谱频率范围与采样区间，实现了较为准确的非线性海面建模。结合海谱与流体动力学理论获得了可靠的破碎波频谱，并对其反演仿真破碎波几何模型。通过合理地选择波浪破碎判据，准确判断出大区域海面上波浪破碎位置，从而将非线性海面与破碎波结合实现复合几何建模。.2. 完成了对高海况海面电磁散射场的数值计算分析。在传统双尺度方法的基础上，对于海面几何模型剖分面元引入相位修正因子，从而实现海面回波幅度和相位的准确仿真。采用高频近似方法分别计算破碎波散射场，并与海面回波进行相干叠加实现海面复合电磁散射数值计算。仿真结果显示出破碎波作为体散射源对于海面散射系数的极化独立效应具有重要影响。.3. 研究了高海况海面电磁散射多普勒谱特征。分析海面几何模型中的非线性项和海浪漂流运动对于海面散射多普勒谱的影响。通过引入波浪水平运动分量，得到与实测多普勒谱相符的数值结果。针对高海况海面外场多普勒谱实测中出现的超级现象，进行包含波浪破碎效应的多普勒谱分析，进而对海尖峰和快散射体等现象的形成原因进行分析讨论。.4. 分析了船生破碎波对于舰船与海面复合电磁散射特性的影响。建立船生破碎波几何模型，并将其引入船体与海面复合电磁散射模型。采用不同船型参数生成各类船生破碎波，并数值计算其雷达散射截面，从而建立船型参数与破碎波散射特征之间联系。通过复合散射场回波多普勒谱仿真发现船生破碎波在大型舰船高速行驶过程中会对电磁散射场造成重要影响。.以上研究成果为复杂海况条件下海面电磁环境建模建立理论基础，在海洋遥感与雷达目标识别技术领域具有广泛的应用前景。