Unambiguous Imaging by a Distributed SAR System With Cross-Track Baselines

Along-track (AT) formations of synthetic aperture radar (SAR) satellites are widely discussed in the literature for their ability to solve the trade-off between resolution and coverage. It is usually assumed that all the satellites in the constellation follow the same orbit with a negligible orbital tube since cross-track (XT) baselines introduce major complexity to high-resolution wide-swath (HRWS) imaging. However, addressing the XT issue is crucial for the feasibility of future formation missions, as realistic orbit control conditions and collision risk considerations will surely impose such baselines. This work discusses HRWS imaging with nonzero XT baselines and derives an algorithm for combining the different channels. The approach differs from traditional methods because the combination is done after focusing, where each target is compressed to several pixels. In this manner, one can address the varying elevation locally. Further performance improvement is obtained by a data-driven definition of the forward model, which utilizes the Matching-Pursuit algorithm to identify the significant ambiguities in each area. The proposed method is highly flexible, as it locally adapts the solution to the actual backscatter and elevation of the scene. Validation and testing were achieved by simulations of X-band acquisition, showing promising results.