Hybrid SAR-ISAR Imaging for Space Target via 2-D Spectrum and SIHR With Spaceborne Radar

Spaceborne hybrid synthetic aperture radar (SAR) and inverse SAR (ISAR) imaging of space targets has a number of advantages in space situational awareness due to the closer observation distance and the strong anti-strike capability. Since both the radar and target are in the high-velocity on-orbit motion state, spatial variant phase errors can be induced, causing the range shift and azimuth spread. Besides, the rotational motion related to scatterers on the target can also lead to a severe image defocusing. In this article, a spaceborne hybrid SAR-ISAR imaging method for space targets via the 2-D spectrum SAR processing and ISAR smoothed integrated high-resolution (SIHR) technique is proposed. First, the slant range model is derived with the spatial variant terms and rotational motion terms existing. Then, the phase errors in the range correction and azimuth processing are analyzed after obtaining the 2-D spectrum of the echo signal. To accurately accomplish range correction, a modified estimation method based on range profiles is proposed to solve the ambiguity of motion parameter estimation caused by the high-velocity motion. Then, based on the given condition of ignoring the phase errors caused by rotational motion terms, azimuth focusing is realized via the SAR processing or ISAR method based on the SIHR. Finally, the spaceborne hybrid SAR-ISAR imaging approach for space targets is proposed. The proposed approach can obtain the well-focused images flexibly without image segmentation. The simulations under three cases and real data results verify the effectiveness of the proposed method in this article.