A Quadtree Beam-Segmenting Fast Backprojection Algorithm

The computation of the backprojection (BP) algorithm for spotlight synthetic aperture radar (SAR) is expensive since the reflectivity reconstruction is based on pixel-by-pixel interpolation operation. Based on dechirp, a quadtree beam-segmenting fast BP algorithm for spotlight SAR is proposed. This fast BP algorithm is to generate multiple sub-beam down-sampled raw data by using dechirp imaging algorithm to filter the whole beam data, and the filtering process is recursively implemented like a quadtree. For any narrow sub-beam, the corresponding sub-image can be reconstructed by a regular backprojection. The pixel numbers of each sub-image is small and the down-sampled sub-beam raw data is small, so it can significantly accelerate the regular BP algorithm. The processing flows are derived in detail and the algorithm is validated by simulated data.