TMSST-RID: A Target-Oriented SAR-ISAR Imaging Method Based on Synchrosqueezing

Synthetic aperture radar (SAR) is an important high-resolution radar system for target surveillance. However, target motion causes a time-varying Doppler frequency in echo and defocused SAR images. To obtain a focused target image, the inverse SAR synthetic aperture radar (ISAR) algorithm is applied: the image is inverted back to the echo and focused using the ISAR imaging algorithm. Clutter significantly impacts the target focusing effect during the SAR-ISAR imaging process. To improve the SAR-ISAR imaging quality of ship targets in the presence of severe sea clutter interference, this article proposes a range instantaneous Doppler method based on the low-rank sparse decomposition and target-oriented multisynchrosqueezing transform (TMSST-RID), which can enhance the target while suppressing clutter. The target area is separated from the clutter area using the low-rank sparse decomposition method. Then, in the time–frequency (TF) analysis, our proposed TMSST method utilizes the prior of the target area to improve the signal-to-clutter ratio (SCR) of the SAR/ISAR image. Compared with the traditional TF transformation, the proposed TMSST enhances the target by sharpening the TF target representation while simultaneously avoiding clutter enhancement. The superiority of this SAR/ISAR imaging method is demonstrated in a performance evaluation using simulated and real radar data for ship targets in sea clutter.