A Novel Motion Compensation Method for High Resolution Terahertz SAR Imaging

Airborne terahertz synthetic aperture radar (THz-SAR) is sensitive to the tiny vibration of the platform because of the short wavelength. Therefore, the phase errors caused by high-frequency vibration of the platform needs to be considered in the motion compensation (MOCO) for THz-SAR imaging. There have been many MOCO methods to compensate the phase errors caused by high-frequency vibration. However, in some cases, the low-frequency motion errors also need to be considered. Different from these methods, this paper proposes a novel MOCO method which compensates both the high-frequency vibration and the low-frequency motion errors. Firstly, the instantaneous chirp rate (ICR) and the instantaneous frequency are both estimated using chirplet decomposition. After filtering out the low-frequency component of the ICR, we obtain the estimate of high-frequency component by using the least squares (LS) sequential estimators. Then, the high-frequency component in the instantaneous frequency is removed, and the parameters of the low-frequency motion are estimated using LS estimator. Finally, the errors are compensated according to the estimated parameters, and the residual phase errors can be compensated by the phase gradient autofocus (PGA) algorithm. The simulation results validate the effectivity of the proposed method.