Synthetic Aperture Radar Drone Gets Interferometric Imaging

Henrik Forstén upgraded his synthetic-aperture radar (SAR) drone with a stronger autofocus algorithm and interferometric imaging capability to overcome earlier resolution limits. The main bottleneck had been GPS position error of about one meter, which blurred images; Forstén improved position estimation and added support for RTK positioning or PPK post-processing to achieve centimeter-level accuracy. The software changes sharpen the radar imagery, and interferometric processing - comparing phase information between repeated flights - lets the system extract elevation information rather than assuming flat terrain.

Hardware improvements accompanied the software: the radar’s phase-locked loop that generates the FMCW frequency sweep was stabilized for cleaner phase data, and the FPGA controller’s SD-card I/O bottleneck was addressed by implementing a simple high-speed compression scheme so raw radar data can be recorded in real time. Forstén’s interferometric workflow flies the same path twice at different altitudes and forms an interferogram to produce detailed elevation maps and correct the apparent leaning of tall objects that single-pass SAR produces. The result is a small, low-cost drone SAR platform capable of high-resolution range and elevation imaging.