High-resolution spotlight spaceborne SAR focusing via modified-SVDS and deramping-based approach

Fine resolution spaceborne spotlight synthetic aperture radar (SAR) imaging is typically affected by the problems of curved orbit and azimuth spectral aliasing, especially when the resolution achieves the decimetre level. In order to overcome these difficulties, a method is proposed here, which consists of the modified singular value decomposition Stolt (SVDS) and the deramping-based approach. The modified SVDS is designed to properly handle the influence induced by curved orbit, and the deramping-based approach is utilised to solve the azimuth spectral aliasing problem. The modified SVDS is derived from the original SVDS by further taking the singular value into consideration, which is more concise and efficient. In addition, the deramping-based approach is combined with numerical differentiation so as to accommodate the situation of curved orbit. The proposed method has smaller phase error and performs better than the generalised omega K method when resolution achieves decimetre level. Experiments carried out on point target simulation validate the effectiveness of the presented method. With focused scene size of 4 by 3 km, the range and azimuth resolutions can achieve 0.15 and 0.14 m, respectively.