Accelerated Back-Projection SAR Processor on Arbitrary Elliptical Imaging Grid With Azimuth Spectrum Unfolding

Recent studies revealed that the time-domain synthetic aperture radar (SAR) processors are more appropriate for future innovative SAR missions (e.g., radar observing system for Europe in L-band (ROSE-L) and Harmony) not only due to their ability to form the SAR image on user-defined regions of interest (ROIs) but also for the straightforward accommodation to configurations wherein the azimuth spectrum folding occurs [e.g., terrain observation with progressive scans SAR (TOPSAR)]. In this letter, we propose an accelerated back-projection (BP) SAR processor working in conjunction with a fast routine for generating the elliptical grid (laying on arbitrary planes) necessary for the subaperture (SA)-based BP speed-up. The proposed workflow forms all the SA SAR images on the same coarse elliptical grid which before the coarse-to-fine grid interpolation are translated in the azimuth baseband. The fine-resolution SAR image is obtained by coherently integrating the SA images together with the concatenation of the corresponding fraction from the azimuth spectrum (unfolding) making the single look complex (SLC) outcome proper for further Doppler-based processing. Our validation experiments indicate that the most suitable family of imaging planes is the one containing the receiver (fan-like grid) on bistatic scenarios with relatively large transmitter-receiver separation. The processing gain has been enhanced by one order of magnitude under low amplitude and phase distortions.