The motion error of a multi-rotor unmanned aerial vehicle (UAV) leads to severe image blurring for mini synthetic aperture radar (SAR) systems. The along-track displacement error usually is compensated in advance through real-time pulse repetition frequency (PRF) adjustment. And then, only the cross-track displacement error is considered in traditional motion compensation (MOCO) algorithms. However, the instantaneous range expression based on the geometry of a squinted SAR shows that the residual along-track displacement error after PRF adjustment cannot be ignored, especially for mini-SAR systems. Therefore, the line-of-sight (LOS) motion error is modified by introducing the residual along-track displacement error. And then, the first and second-order factors for the LOS MOCO are redefined. The experimental results show that the proposed method can reduce the LOS motion error and significantly improve the imaging performance of the squinted SAR mounted on a multi-rotor UAV.

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