Geometric distortions in FMCW SAR images due to inaccurate knowledge of electronic radar parameters: analysis and correction by means of corner reflectors

• Published in: Remote sensing of environment Vol. 232; p. 111289
• Main Authors: Esposito, C., Natale, A., Palmese, G., Berardino, P., Perna, S.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01-10-2019; Elsevier BV
• Subjects: Airborne SAR; Algorithms; Continuous radiation; Corner Reflectors; Data acquisition; Distortion; FMCW SAR; Helicopters; Low altitude; Onboard equipment; Parameters; Radar; Radar data; Radar equipment; Radar parameter estimation; Reflectors; Superhigh frequencies; Synthetic aperture radar; Synthetic Aperture Radar (SAR); Airborne SAR; Radar parameter estimation; Corner Reflectors; Synthetic Aperture Radar (SAR); FMCW SAR
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2019.111289

In the last years the Frequency Modulated Continuous Wave (FMCW) technology has been playing an ever greater role in the realization of compact, light and cheap Synthetic Aperture Radar (SAR) systems to be mounted onboard small, low altitude platforms such as airplanes, helicopters and drones.
To correctly focus FMCW SAR images, it is necessary to accurately know some system parameters, including the frequency sweep rate of the signal transmitted by the radar. It may happen, however, that this frequency sweep rate is not very accurately measured by the radar provider, and thus an incorrect value of this parameter is used during the SAR data focusing procedure. This may produce serious geometric distortion effects in the focused FMCW SAR images. To circumvent these problems, in this work we present a procedure that estimates the frequency sweep rate actually employed by the FMCW radar, thus providing a key information that can be then profitably used to achieve the correct focusing of the SAR data acquired by the radar system at hand. More specifically, we propose an algorithm that exploits on one side the focused SAR images corrupted by the geometric distortion effects induced by the inaccurate knowledge of this radar parameter, and on the other side the very precise in-situ measurements of the positions of a limited number of Corner Reflectors (CRs) properly deployed over the observed scene.
The effectiveness of the proposed algorithm has been tested on real data acquired by an airborne X-band FMCW SAR system.
•The algorithm estimates the actual FMCW radar frequency sweep rate.•The presented approach makes use of in-situ measurements on Corner Reflectors.•The algorithm leads to a range misalignment smaller than the system resolution.