Synthetic aperture radar (SAR) is important for marine surveillance. The image resolution of SAR is obtained via coherent integration. However, with increasing coherent processing intervals (CPIs), the focusing quality of maneuvering ships in images will worsen, impacting target recognition. Defocusing is caused mainly by the change in the image projection plane (IPP) of the maneuvering ship and the change in the effective rotation vector (ERV). In this article, an improved inverse SAR (ISAR) method is used to focus the ships in SAR images. First, the factors influencing the instantaneous imaging position are analyzed. Then, a new method based on data resampling for maneuvering ship imaging with a long CPI is proposed. This method consists of two main steps: ERV estimation and data resampling. The change in the ERV is estimated by using the instantaneous imaging position of all the scatterers, and the ship echo is resampled according to the estimation of the time-varying ERV. After resampling, we can obtain the echo from a constant rotating ship and can ensure a well-focused ship by using the traditional range-Doppler algorithm. This new method overcomes the restriction of ERV variation. Thus, a longer CPI can be used for imaging, while the IPP remains stable. Finally, simulation and measured data are used to verify the effectiveness of the proposed algorithm.

中文翻译：

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通过数据重采样增加机动船舶SAR聚焦的相干处理间隔

合成孔径雷达（SAR）对于海洋监视非常重要。 SAR的图像分辨率是通过相干积分获得的。然而，随着相干处理间隔（CPI）的增加，图像中机动船舶的聚焦质量会变差，影响目标识别。散焦主要是由机动船的图像投影平面（IPP）的变化和有效旋转矢量（ERV）的变化引起的。在本文中，使用改进的逆SAR（ISAR）方法对SAR图像中的船舶进行聚焦。首先，分析了影响瞬时成像位置的因素。然后，提出了一种基于数据重采样的长CPI机动船舶成像新方法。该方法由两个主要步骤组成：ERV 估计和数据重采样。利用所有散射体的瞬时成像位置来估计ERV的变化，并根据时变ERV的估计对船舶回波进行重采样。重采样后，我们可以获得来自不断旋转的船舶的回波，并且可以使用传统的距离多普勒算法确保船舶聚焦良好。这种新方法克服了 ERV 变化的限制。因此，可以使用较长的 CPI 进行成像，同时 IPP 保持稳定。最后利用仿真和实测数据验证了所提算法的有效性。