A novel imaging algorithm is presented in this article for focusing the very high resolution spaceborne synthetic aperture radar (SAR) data of spotlight mode. The long synthetic aperture time in spotlight mode brings new problems, such as Doppler spectrum aliasing and curved orbit. The imaging results will be filled with ambiguity and would suffer from resolution reduction if Doppler spectrum aliasing is not handled. The error introduced by curved orbit will degrade resolution of the target and introduces asymmetric sidelobes in azimuth direction. The start–stop approximation is no longer applicable, since it introduces two effect, e.g., “fast-time” effect and “slow-time” effect, which will cause defocusing and range-dependent azimuth shift, respectively if not handled. The proposed algorithm combines the two-steps processing approach (TSPA) and the backprojection algorithm (BPA). First, the initial step of TSPA is used to get a high azimuth sampling rate which is higher than pulse repetition frequency to avoid the Doppler spectrum aliasing. Then, the “fast-time” effect of start–stop approximation is corrected in the 2-D frequency domain. Finally, the BPA is used to correct the error introduced by the curved orbit and the “slow-time” effect of start–stop approximation. The experimental results of spaceborne SAR data acquired by Gaofen-3 (GF-3) SAR system demonstrate the feasibility of the proposed algorithm.

中文翻译：

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具有不启停模型的超高分辨率GF-3 SAR聚光灯数据处理及弯曲轨道修正

本文提出了一种新的成像算法，用于聚焦聚光灯模式的超高分辨率星载合成孔径雷达 (SAR) 数据。聚光灯模式下较长的合成孔径时间带来了新的问题，如多普勒频谱混叠和弯曲轨道。如果不处理多普勒频谱混叠，成像结果将充满模糊性，并且会降低分辨率。弯曲轨道引入的误差会降低目标的分辨率，并在方位角方向引入非对称旁瓣。起止近似不再适用，因为它引入了两种效应，例如“快时间”效应和“慢时间”效应，如果不加以处理，这将分别导致散焦和依赖于距离的方位角偏移。所提出的算法结合了两步处理方法（TSPA）和反投影算法（BPA）。首先，TSPA的初始步骤用于获得高于脉冲重复频率的高方位采样率，以避免多普勒频谱混叠。然后，在二维频域中校正起止近似的“快速时间”效应。最后，BPA 用于校正由弯曲轨道和起止近似的“慢时间”效应引入的误差。高分三号（GF-3）SAR系统获取星载SAR数据的实验结果证明了该算法的可行性。起止近似的“快速时间”效应在二维频域中得到校正。最后，BPA 用于校正由弯曲轨道和起止近似的“慢时间”效应引入的误差。高分三号（GF-3）SAR系统获取星载SAR数据的实验结果证明了该算法的可行性。开始-停止近似的“快速时间”效应在二维频域中得到校正。最后，BPA 用于校正由弯曲轨道和起止近似的“慢时间”效应引入的误差。高分三号（GF-3）SAR系统获取星载SAR数据的实验结果证明了该算法的可行性。