High-Order Rotational-Migration Correction and ISAR Imaging in the THz Band Considering Impact of Scattering Intensity

The high-resolution inverse synthetic aperture radar (ISAR) imaging of space target holds tremendous significance for recognition and on-orbit maintenance. The terahertz (THz) radar possesses natural superiority in terms of large bandwidth and short wavelength, enabling it to achieve higher resolution both in range and azimuth directions. However, the range cell migration (RCM) induced by rotation is severe in the THz band, even in small rotation angle. In order to achieve high-accuracy RCM correction, an imaging algorithm based on keystone transform (KT) and fast Gaussian gridding nonuniform fast Fourier transform (FGG NUFFT) is presented in this article. Nevertheless, to correct the second-order RCM and compensate the spatial-variant (SV) phase error, the rotation parameters of uncooperative target need to be estimated first. Moreover, by analyzing the ISAR images of space targets, it is found that the scattering intensity of certain components on the satellite body, such as the cavity structure of the antenna, is stronger than that of the solar panels. Considering scattering intensity of these components, the traditional estimation method under global image quality criteria may fail. To prevent getting trapped in a local optimum or finding an incorrect solution due to the influence of strong scattering points, a parameter estimation framework based on prior knowledge added sparrow search algorithm (PKSSA) under local maximum contrast criterion (LMCC) is brought forward. The proposed novel algorithm can not only fast estimate rotation parameters without being affected by strong scattering points but also obtain fine imaging results. Numerous electromagnetic simulation and real measured THz experiment results prove the correctness and effectiveness of the proposed algorithm.