High Cross-Range Resolution Imaging Approach for Space Targets via CRRC and Nonuniform Resampling With Spaceborne ISAR

For spaceborne inverse synthetic aperture radar (ISAR) imaging of space targets, the large relative velocity can lead to a significant view angle change between the radar and targets. It also causes the nonlinear high-order time-varying couplings between the velocity and cross range, which can introduce the 2-D spatial-variant errors. However, benefiting from the variability of relative motion states between satellites, these couplings can contribute to an obvious increase in the equivalent rotation angle during a short time interval. Therefore, by effectively utilizing the nonlinear components, a higher cross-range resolution can be achieved to make images contain more information about the target. In this article, a spaceborne ISAR imaging approach for space targets aimed at improving cross-range resolution is proposed. First, the detailed geometry of spaceborne ISAR imaging of space targets is established. Then, the feasibility analysis and the boundary conditions of improving cross-range resolution using the nonlinear terms are presented analytically. According to the given conditions, the cross-range rotation compensation (CRRC) should be accomplished first, and a CRRC method based on the parameter estimation of multiple scatterers is proposed. Subsequently, to maximize the improvement in cross-range resolution, a slow-time nonuniform resampling method with selecting the optimum processing time interval is proposed. Finally, the spaceborne ISAR imaging approach for space targets is proposed. The approach can simultaneously achieve a higher cross-range resolution and eliminate the azimuth defocusing caused by nonlinear components, enhancing the quality of ISAR images. The effectiveness of the proposed approach is verified through simulation and real data results.