含卷浪海面上方低空目标复合散射特性及耦合机理分析

The overturning wave crest is considered as one of the main reasons to the sea-spike phenomenon. The signals of sea spikes are similar to those of target, which has a great influence on the detection and recognition of low-altitude target above the sea surface. As a result of the urgent demands of the look-down radar in the complex marine environment for the detection and recognition of low-altitude target, this project will focus on the investigation of composite scattering characteristics and coupling mechanism of the low-altitude target above three-dimensional complex sea surface with overturning wave crest by the electromagnetic modeling. The SBR/PTD method, Integral Equation Model and the multipath thought are utilized to compute the scattering of low-altitude target and sea surface with overturning wave crest as well as the coupling scattering between the target and sea surface with overturning wave crest, respectively. Then the GPU and CUDA parallel acceleration techniques are adopted to further improve the simulation efficiency, and the composite scattering model is established. The influence of overturning wave crest's profile and target's altitude angle on the coupling scattering is investigated, and the variation of composite scattering with the radar parameters, ocean condition, profile of overturning wave crest as well as the height and altitude angle of target will be analyzed, revealing the complicated coupling mechanism between the low-altitude target and sea surface with overturning wave crest. This project will provide a theoretical foundation and technical support for the detection and recognition of low-altitude target above sea surface with overturning wave crest as well as radar imaging, etc.

卷浪是‘海尖峰’现象产生的主要原因之一，‘海尖峰’信号与目标信号相似，对海上低空目标的探测和识别造成直接影响。鉴于复杂海洋环境中下视雷达对海上低空目标探测和识别的迫切需求，本项目拟通过电磁理论建模的途径开展三维含卷浪复杂海面上方低空目标复合电磁散射特性及耦合机理研究。具体包括：采用SBR/PTD、积分方程法以及多路径思想分别求解低空目标散射、含卷浪海面散射以及目标与含卷浪海面之间的耦合散射，并结合GPU和CUDA并行加速技术，建立三维含卷浪复杂海面上方低空目标复合电磁散射模型；探索卷浪几何形态以及目标姿态角对耦合散射的影响，分析含卷浪海面上方低空目标复合散射随雷达参数、海况参数、卷浪几何形态、目标高度以及姿态角等因素的变化规律，揭示含卷浪海面与低空目标之间复杂的电磁耦合机理，旨在为含卷浪海面上方低空目标的探测、识别以及雷达成像等提供一定的理论依据和技术支持。

本项目重点针对含卷浪复杂海面上方低空目标电磁散射特性及耦合机理展开研究，从三维时变卷浪精细几何建模着手，采用碎浪生命周期的方法模拟卷浪不同阶段几何轮廓的变化, 并引入风速、时间因子、表面微粗糙的影响，同时结合二维卷浪模型库法建立三维改进时变卷浪精细几何模型；在此基础上，将三维卷浪与海面相结合，并对卷浪与海面相连接区域进行插值处理，保证模型的连续性，建立了三维含卷浪海面几何模型。从电磁波与目标以及海面之间的相互作用机理出发，采用半确定面元+射线追踪+PTD混合算法，求解三维含卷浪海面散射、目标多次散射和棱边绕射、目标和海面以及卷浪之间的多次耦合散射，进一步结合邻域搜索、双向追踪以及GPU并行加速技术提升仿真精度以及仿真效率，建立了含卷浪复杂海面上方低空目标复合电磁散射模型，并将仿真结果与数值精确算法进行对比验证仿真模型的有效性。基于大量仿真数据，研究了卷浪几何形态对复合散射特性的影响，分析了含卷浪海面与低空目标耦合散射随卷浪几何形态以及目标姿态角变化情况。根据本项目研究结果可知，卷浪是产生“海尖峰”现象的主要原因之一，当海面存在卷浪时，卷浪与海面之间存在多次散射的多次散射以及“布儒斯特”效应是HH极化散射强度大于VV极化散射强度的根本原因；“海尖峰”现象在逆风小擦地角条件下发生的概率较高；随着海面上方风速以及入射频率的不断增大，“海尖峰”现象变得更加明显，由卷浪产生的强散射回波呈现一定的“类目标”特性，对低空目标的探测产生重要影响。本项目研究成果将为复杂海背景中低空目标SAR回波仿真提供数据支撑，为“海尖峰”背景下低空目标的探测和识别技术研究提供一定的技术支持，对优化雷达系统涉及具有十分重要的应用前景。