Low-Altitude Wide-Swath SAR Interferometry for UAV-Borne Radar

Kurzfassung

Synthetic aperture radar (SAR) interferometry based on Uncrewed Aerial Systems (UASs) enables highly flexible and cost-efficient measurements, but the low-altitude flight regime introduces fundamental challenges. Short sensor-to-target ranges require wide antenna beams to achieve sufficient azimuth resolution according to the SAR principle, which in turn induce large angular variations across the synthetic aperture. These variations strongly affect SAR image formation and interferometric coherence, and cannot be reliably handled with conventional processing methods developed for spaceborne or fixed-wing platforms. This paper introduces a dedicated signal processing approach specifically tailored to UAS-based single-pass SAR interferometry (InSAR). The method explicitly incorporates the platform's time-varying geometry and uses backprojection as the underlying algorithm, providing the flexibility to accommodate nonlinear flight trajectories and a wide range of angles. Surface topography is estimated via phase progression across multiple focusing heights, effectively mitigating the ambiguities and error propagation associated with classical phase unwrapping. A detailed analysis of each stage in the processing pipeline - including raw data handling, SAR image formation, and interferometric phase processing - is presented to highlight the influence of geometric effects. Experimental validation based on single-pass UAS measurement campaigns with a frequency-modulated continuous-wave (FMCW) radar demonstrates the reliable generation of high-resolution digital elevation models (DEMs). The results confirm that the proposed approach remains effective under the challenging low-altitude, wide-swath conditions and is well suited for accurate and robust local-scale topographic monitoring.