Airborne X-band SAR imaging with 10 cm resolution - technical challenge and preliminary results

RAMSES airborne SAR system bandwith was recently increased to 1.2 GHz in X and Ku bands, yielding (unweighted) 3 dB range resolution of 11 cm. Synthesis of SAR images with matching cross-range resolution, requires long integration time thus disqualifies temporal-domain back-injection synthesis algorithm as impractically slow. The wider relative bandwidth also disqualifies simplified range/Doppler types of algorithms because the hypothesis of proportionality between Doppler and squint is no more valid. Therefore, we implemented a fast frequency-domain synthesis algorithm (Ω-k or range-migration algorithm) and designed a new deterministic motion and antenna pattern compensation method for it. Since the required accuracy on carrier trajectory exceeded the performance of our differential GPS-hybridized inertial navigation unit, we implemented an autofocus based on the phase tracking of several isotropic point-like echoes. Since the resolution cell is only a few wavelength wide, clutter appearance and statistics is unusual. We present here some typical examples for high resolution clutters and compare with texture simulations from optical 2 1/2 D surface modelling.