Parametric scatterer extraction method for space-target inverse synthetic aperture radar image CLEAN

Owing to the time variance of the inverse synthetic aperture radar (ISAR) imaging plane of space targets, scatterers with large heights relative to the imaging plane migrate through several Doppler cells. This defocussing in the azimuth direction of each scatterer cannot be compensated via the traditional migration through the resolution cell (MTRC) compensation method because the height of each scatterer is quite different and independently distributed in the ISAR image. In this study, a parametric azimuth-defocussing model-based CLEAN method is proposed for the space-target ISAR image. First, high-order defocus parameters and their influences on the image of space targets were analysed at different arc segments. Subsequently, a mathematical azimuth-defocussing expression of the ISAR image scatterers was derived after MTRC and azimuth high-order phase compensation, and an approximate defocus expression based on the Fresnel integral was provided for computational efficiency. This model can estimate the complex amplitude, coordinates and defocus parameters of each scatterer in the image domain by applying a sequential quadratic programing algorithm. Finally, the validity and stability of the proposed algorithm for the isolated and coupled scatterer extraction were verified at different signal-to-noise ratios, and different defocus parameters were verified through simulations.