Abstract: Based on studying the Doppler center in SAR processing, a correlation Doppler estimator method is proposed in the paper, which is based on frequency modulation and accords to the unstable problem of traditional method in unwrapping. The proposed algorithm solves the wrapped Doppler center by modulating signal into unwrapped field. During the processing, the method updates modulating frequency by least square method in order to get stable Doppler center, and then new algorithm solves the unstable problem, and it is more stable than the traditional method. The raw data imaging results show it is effective for SAR processing.

Key words: Synthetic Aperture Radar（SAR）, Doppler frequency estimator, correlation Doppler estimator, unwrapping

摘要： 对SAR成像中多普勒中心频率进行研究，指出传统多普勒中心估计，在解卷绕过程中，会存在不稳定问题。针对这一问题，提出了一种基于频率调制的时域相关估计算法。该算法将多普勒中心搬移到非卷绕区，避免了卷绕出现；估计过程中使用最小二乘法更新调制频率，适应多普勒中心变化，保证了估计的稳定性，该算法相比传统估计算法，解决了传统算法不稳定问题，具有更强的适用性。最后通过真实的机载SAR数据，验证了该算法的有效性。

关键词: 合成孔径雷达, 多普勒频率估计, 时域相关估计算法, 解卷绕