Spherical Geometry Algorithm for Spaceborne Synthetic Aperture Radar Imaging

Higher spatial resolution and larger imaging scene are always the goals pursued by advanced spaceborne synthetic aperture radar (SAR) system. High-resolution and wide-swath SAR imaging can provide more information about the illuminated scene of interest on the one hand but also come with some new challenges on the other. The induced new challenging problems include curved orbit, Earth’s rotation, and spherical ground surface. Most existing image formation algorithms suffer from performance deficiency in these challenging cases, either in focus accuracy or computational efficiency. In this article, an accurate Fourier transform relationship between the phase history domain data and the scene reflectivity function is derived under an arbitrary radar trajectory by exploiting the spherical geometry property of the spaceborne SAR data collection. Using the derived new data model, an image reconstruction algorithm based on Fourier inversion is proposed. The new algorithm has the inherent capability of correcting for the curved orbit and spherical ground surface effect. Meanwhile, the out-of-plane motion effect induced by the Earth’s rotation can also be compensated by a two-step phase correction and data projection procedure embedded in the Fourier inversion reconstruction. The new algorithm inherits the merits of both time domain and frequency domain algorithms and has excellent performance in both focus accuracy and computational efficiency. Both simulation and real data processing results validate the effectiveness of the proposed imaging algorithm.