Generation of Accurate, High-Resolution Digital Elevation Models From Ultrawideband, Drone-Borne, Repeat-Pass Interferometric SAR

Synthetic aperture radar (SAR) interferometry (InSAR) is a remote sensing technique that allows the generation of digital elevation models (DEMs) by combining two complex SAR images taken with a certain across-track separation. DEMs are of paramount importance for monitoring the Earth's surface and have traditionally been obtained using space- and airborne SAR systems, which are, however, characterized by stringent bandwidth regulations, constrained revisit times, and costly deployment and operation. Drone-borne InSAR enables cost effective surveillance of local areas with unprecedented accuracy and resolution through the exploitation of wider bandwidths and has therefore emerged as an attractive complementary system with short deployment times and flexible revisit intervals. This paper shows how to generate accurate, high-resolution DEMs through multiple acquisitions performed by a radar with ultrawide fractional bandwidth onboard a drone. We discuss the impact of the characteristics of the system and the acquisition parameters on the quality of the resulting DEMs. We also present a SAR processing scheme based on the omega-k algorithm, which allows fast processing of the drone-based raw SAR data and still yields comparable quality as back-projection algorithms, and an InSAR algorithm that takes into consideration the wide bandwidth of the system and exploits it to support phase unwrapping using radargrammetry. An experimental demonstration is conducted showing that DEMs with a height accuracy of a decimeter can be obtained at an independent posting of 25 cm × 25 cm. The system presented in this paper enables the generation of very high-quality DEMs with very short temporal baselines and also represents an important step towards the realization of single-pass distributed drone-based InSAR systems in the future.