A THz-ISAR imaging and rotation parameter estimation method for non-uniformly rotating targets based on minimum entropy

Since there is no atmospheric influence, space-based terahertz inverse synthetic aperture radar (THz-ISAR) can obtain high-resolution images of space targets at a certain distance, so it has important application prospects. In addition, the relative motion of space-based platforms and space targets is complicated. For some satellites that are tumbling out of control or are undergoing attitude change, the imaging angle formed by the target relative to the radar can be considered to be non-uniform, which in turn leads to imaging defocus.In this paper, a minimum entropy-based THz-ISAR rotation parameter estimation and motion compensation method for nonuniformly rotating space targets is proposed. Firstly, the radar echo is compensated for the translational motion and corrected for the range migration to obtain an envelope-aligned one-dimensional range profile. Then, the minimum entropy (ME) algorithm based on Newton’s method (NM) is used to estimate rotational velocity and centre of the targets, and to compensate the range second-order spatial-variant (SV) phase. After that, the golden section method is applied to estimate the target rotational acceleration and compensate the azimuth second-order spatial-variant phase. Finally, the cyclic variable method is used to iterate these two compensation steps alternately to avoid the coupling effect of range and azimuth second-order spatial-variant phase, while obtaining the target rotation parameters and the well-focused imaging results.