临近空间宽域高分辨SAR成像技术研究

【作者】 周宝亮；

【导师】 田忠；

【作者基本信息】 电子科技大学 ， 电路与系统， 2011， 硕士

【摘要】 临近空间(Near-space)一般指高度为20~100千米之间的区域,而临近空间合成孔径雷达(Synthetic Aperture Radar, SAR)是一种新型遥感SAR,通过搭载在气球、飞艇或机动飞行器等临近空间平台上来获取地面目标二维高分辨率图像。论文以临近空间快速平台SAR为研究背景,开展了临近空间方位多波束SAR成像技术和分布式SAR成像技术研究。在分析非均匀采样对方位向成像影响的基础上,提出了一种基于分数阶傅立叶变换的方位多波束非均匀信号频谱重构算法;将方位多波束技术与距离向宽带信号合成技术相结合,实现了临近空间宽测绘带高分辨率SAR成像;提出了一种基于Legendre展开的非线性CS成像算法,实现了临近空间分布式SAR高精度成像。论文主要包括以下内容:1.针对临近空间单平台SAR,研究了基于偏移相位中心的方位多波束成像技术。建立了单发多收和多发多收成像信号模型,实现了均匀采样条件下方位多波束成像。分析了非均匀采样对方位向成像的影响,提出了一种基于分数阶傅立叶变换的方位多波束非均匀信号频谱重构算法,并通过仿真验证了算法的有效性。分析了方位向多普勒模糊产生的原因,研究了基于等效相位中心的空域滤波解模糊技术,实现了方位向宽带信号的合成。2.将方位多波束技术与距离向宽带信号合成技术相结合,实现了临近空间宽测绘带高分辨率SAR成像。详细推导了距离向宽带信号合成和非线性CS成像算法,并通过点目标的正侧视和斜视成像结果验证了该方法的有效性。3.针对临近空间分布式SAR成像技术特点,提出了一种基于Legendre展开的非线性CS成像算法。文中给出了NCS调频率,Chirp Scaling操作因子以及距离向和方位向压缩等关键函数的表达式。在斜视角为0o ,30o,45o和50o的情况下分别用基于Legendre展开的NCS成像算法和用基于Taylor展开的NCS成像算法对点目标进行成像。通过对比仿真结果,得出了在临近空间SAR大斜视工作模式下,Legendre多项式有效的改善了NCS算法的成像质量。更多还原

【Abstract】 Near Space generally refers to the altitude which is between 20 and 100 km region, while the Near Space Synthetic Aperture Radar (SAR) is a new type of remote sensing SAR, which gets the targets’two dimensional high-resolution images, has been carried with the balloon, airship or aircraft and others Near Space platforms.Who’s the research background is Near Space quick platform SAR, the paper is mainly on the multiple azimuth beams and distributed SAR imaging. After analyzing the reason that the echo signal are sampled in non-uniformly and its influence, a novel spectrum reconstruction algorithm based on Fractional Fourier Transform (FrFT) for multiple azimuth beam SAR is presented. It is utilized to carry out Near Space high-resolution and wide-swath SAR imaging simultaneously by integrating the multiple azimuth beam technology and wideband signal synthesis technology. A novel nonlinear CS imaging algorithm based on Legendre polynomial is proposed, which improves the approximation accuracy, and realizes Near Space distributed SAR high-precision SAR imaging. Paper includes the following:1. On the basis of the Near Space signal platform SAR, paper has a detailed analysis of displacing phase centre multibeam technology. First, we established the signal model of Single Transmitter Multiple Azimuth Beams and Multiple Transmitter Multiple Azimuth Beams and realized uniform sampling SAR imaging. Second, the influence of non-uniform sampling for SAR imaging has been derived and a novel spectral reconstruction algorithm for multiple azimuth beams SAR based on the FrFT theory was presented, simulation results were proposed to verify the results. Finally, we given the reason of azimuth ambiguities, based on the theory of equivalent phase center space filters to remove azimuth ambiguities by using the abundant space resources in multiple azimuth beam SAR system and achieved the wideband signals synthesis in azimuth direction.2. It is utilized to carry out Near Space high-resolution and wide-swath SAR imaging simultaneously by integrating the multiple azimuth beam technology and wideband signal synthesis technology. In this paper, a detailed formula was derived on the wideband signal synthesis and the nonlinear CS imaging algorithm. Through analysis of point targets imaging results in the positive side and squint modes, we verify the system is feasibility and effectiveness.3. Based on the distributed SAR imaging’s characteristic, a novel nonlinear CS imaging algorithm based on Legendre polynomial expansion is proposed. We have given the expression of NCS chirp rate, Chirp Scaling Operation factor, range matching function, the azimuth matching function and others. In the case of squint 0o , 30o , 45o and 50o , we use the NCS imaging algorithm based on the Legendre expansion and the Taylor expansion respectively to realize the point targets imaging. Compared with the simulation results at different angles, we get the Legendre polynomial improves the NCS imaging algorithm effectively in high squint mode SAR.更多还原