基于时域算法的海上低空目标宽带散射及HRRP特性分析

Usually, the low-altitude target has some advantages over other one, such as a high speed, strong clutter environment, and good concealment. So the detection and identification of low-altitude target has always been a difficult question in the field of radar technology. In view of the urgent demand of the look-down radar in the marine environment for the radar signature of low-altitude target, in the project the composite wide-band scattering and high-resolution range profile (HRRP) of the low-altitude target above rough sea surface are investigated by the electromagnetic modeling. Specially, the hybrid method of FDTD-TDPO and high frequency method of TDPO combined with TDEEC are adopted to built the model of composite wide-band scattering from the low-altitude target above sea surface. Then the HRRP of low-altitude target above sea surface is obtained by an inverse discrete Fourier transform. It is revealed that the complex electromagnetic coupling mechanism between low-altitude target and rough sea surface. The source of the peaks in HRRP of low-altitude target above sea surface is analyzed, as well as the sensitivity of HRRP for the pose of target. The multi-parameter models of the wide-band scattering and HRRP from the low-altitude target above sea surface are built tentatively, which are related to the parameters of radar, sea state, and target. The physical mechanism of the characteristic of wide-band scattering and HRRP is focused for the high resolution radar, large incidence angle, and high sea state. The project will provide a theoretical basis for the detection and recognition of low-altitude target above sea surface, radar imaging, and technology of low-altitude penetration, etc.

低空目标通常具有飞行速度快、背景杂波干扰强、隐蔽性好等优势，因此对低空目标的检测识别一直是雷达技术领域的难点问题。鉴于海洋环境中下视雷达对低空目标雷达特征信号的迫切需求，本项目将通过电磁理论建模的途径开展粗糙海面上方低空目标的复合宽带散射及高分辨距离像(HRRP)特性研究。具体包括采用FDTD-TDPO混合方法、TDPO结合TDEEC的高频方法建立海上低空目标的复合宽带散射模型，进而利用离散傅里叶逆变换得到海上低空目标的HRRP；揭示低空目标与海面之间复杂的电磁耦合机理，开展海上低空目标HRRP中峰值的来源分析及HRRP对目标姿态的敏感性分析，探索建立海上低空目标的宽带散射及HRRP随着雷达、海况及目标参数变化的多参数关联模型，并着重研究雷达高分辨率、大角度入射、高海情下宽带散射及HRRP特征的物理机理，旨在为海上低空目标的检测与识别、雷达成像、低空突防技术等提供一定的理论依据。

鉴于实际海洋环境中下视雷达对低空目标雷达特征信号的迫切需求，本项目通过电磁理论建模的途径开展了粗糙海面上方低空目标的复合散射及高分辨距离像(HRRP)特性研究。利用迭代物理光学法(IPO)研究了一维高海情下粗糙海面的电磁散射、一维粗糙(海)面与二维低空目标(上方、半掩埋、多目标)的复合散射及多普勒频谱、二维分层粗糙面的电磁散射、二维粗糙面与三维涂覆目标的复合散射，基于宽带回波数据分析了一维粗糙海面上方二维目标的一维高分辨距离像(HRRP)特征；以及采用IEM-PO混合方法研究了高海情下海面与上方低空目标的复合散射。本项目中IPO方法采用等效原理和多路径散射思想处理海面和低空目标之间的耦合散射过程，关于粗糙海面与低空目标复合模型的电磁散射均与文献中MOM和FE-BI-KA的进行了比较，结果表明IPO方法在保证精度的前提下极大地节省了计算机资源。并且详细分析了不同雷达参数(频率、入射角、极化)、不同海况参数(风速、盐度、温度)、不同目标参数(类型、速度、高度)下复合模型的电磁散射规律及物理机理。.另外本项目超额完成了两部分工作：采用基于双尺度模型的射线追踪算法(TSM—RT)快速计算了电大尺寸海面电磁散射，与传统的射线追踪算法相比，在保证计算精度的情况下，该算法能够有效减少射线与面元的求交次数。同时，为了进一步减少计算时间，还利用GPU并行技术对TSM-RT算法进行加速；运用快速多极子方法(FMM)结合压缩感知技术(CS)技术快速分析了三维复杂目标的多站电磁散射。该算法将目标多站电磁散射中的散射场看作是入射角和散射角的二维函数，当对该散射场进行离散时就自然而然形成一个二维数组，再将该二维数组看作CS中的待处理的信号，对其进行稀疏采样得到目标的多站电磁散射结果。.本项目的研究将为海上低空目标的检测与识别、雷达成像、低空突防技术等提供一定的理论依据。