Extended three-step focusing algorithm for spaceborne sliding spotlight SAR image formation
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摘要: 针对星载SAR(Synthetic Aperture Radar)滑动聚束成像模式,结合空间几何模型沿距离向对混合度因子进行了分析及修正.在此基础上研究了单点目标及全场景的多普勒带宽,并通过数学推导验证了两步成像处理算法克服频域混叠的有效性.通过进一步深入研究指出了两步成像算法的局限性,即对脉冲重复频率的选择具有较高的要求,否则在方位向图像域造成混叠.针对两步成像算法的缺陷提出三步扩展成像处理算法,在方位向聚焦后通过选择合适的deramp因子完成方位向的重采样,克服了方位向图像域的混叠,并研究了第三步deramp操作对方位向时域展宽的影响.最后通过仿真验证了三步成像处理算法的优越性.Abstract: Aimed at spaceborne sliding spotlight synthetic aperture radar(SAR) imaging mode, the hybrid factor was analyzed and amended along the range direction combined the geometry model firstly. Based on the analysis, the Doppler bandwidth of both single target and whole scene were researched, and the validity of the two-step approach to overcome azimuth spectrum aliasing was proved by mathematic derivation. Moreover, the limitation of two-step approach was illuminated by thorough research. Namely, the azimuth overlapping will appear in image domain without high pulse repetition frequency. A extended three-step focusing algorithm was presented to resolve the disadvantage of two-step approach. After azimuth data focusing, a deramp operation was adopted to finish the resample in azimuth with a selected deramp factor, by which the azimuth overlapping in image domain was overcome. And, the azimuth time extension caused by deramp operation was also researched. Finally, the simulation results justify the superiority of the extended three-step algorithm.
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Key words:
- synthetic aperture radar /
- sliding spotlight /
- two-step approach /
- derotation
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