多方位角融合SAR图像中“扇形”旁瓣分析

Fan-shaped Sidelobes Analysis in Multi-azimuth-angle Fusion SAR Images

随着相控阵天线电子扫描能力的提升,多方位角观测成为星载合成孔径雷达(Synthetic Aperture Radar,SAR)发展方向之一,从多维度提高目标信息解译能力。然而,在公开的多方位角融合SAR图像中存在较强的二维“扇形”旁瓣现象,且二维分布特点不同,容易造成目标误判。因此本文针对此旁瓣方向和多方位角观测目标分辨率开展研究。首先,概述了多方位角观测模式和特性,提出了基于CUDA并行加速的快速后向投影(Back Projection,BP)算法,高效率生成多方位角序贯SAR图像,避免耗时的图像配准和几何校正;其次,基于多方位角观测中斜距平面和地距平面的几何投影关系,重点分析了地距平面目标方位向、距离向分辨率和旁瓣方向,揭示了融合SAR图像中“扇形”旁瓣的形成机理,并解释了二维旁瓣特性不同的原因,基于此可反演获取该SAR图像时卫星和观测场景之间的几何关系,以及融合SAR图像数;最后,通过点目标和扩展目标仿真开展实验,结果表明方位斜视观测中,地距平面方位向、距离向分辨率理论分析精度优于0.02 m,旁瓣方向理论分析精度优于1o,验证了所提分析方法的正确性。

The improvement of phased array antenna in electronic scanning ability has made the multi-azimuth-angle mode one of the development directions of spaceborne synthetic aperture radar(SAR),which can interpret the target information from multiple dimensions.However,a strong two-dimensional“fan-shaped”sidelobe phenomenon exists in the publicly available multi-azimuth-angle fusion SAR images with different two-dimensional distribution characteristics,leading to the target misjudgment.Therefore,this paper focuses on the“fan-shaped”sidelobe phenomenon and target resolution.First,the multi-azimuth-angle mode is introduced,and a fast back-projection(BP)algorithm based on CUDA parallel computing is proposed for efficiently generating sequential SAR images.This imaging method can avoid time-consuming image registration and geometric correction.Then,based on the geometry relationship between slantrange plane and ground-range plane of multi-azimuth-angle SAR,the resolution and sidelobe direction along azimuth and range direction on the ground-range plane are analyzed.The analyses reveal the origin of“fan-shaped”sidelobes in fusion SAR images and provides the reasons for the different characteristics of two-dimensional sidelobes.As a result,the geometric relationship between the satellite and the observation scene and the number of fused images are derived.Finally,the effectiveness of the proposed analysis results of the“fan-shaped”sidelobe is verified using point targets and through the extended targets simulation experiment.The experimental results indicate that the accuracy of resolution analysis along both the ground azimuth and range directions is better than 0.02 m and that of the sidelobe direction is better than 1°.