Airborne Synthetic Aperture Radar (SAR) systems are gaining increasing interest within the remote sensing community due to their operational flexibility and observation capabilities. Among these systems, those exploiting the Frequency-Modulated Continuous-Wave (FMCW) technology are compact, lightweight, and comparatively low cost. For these reasons, they are becoming very attractive, since they can be easily mounted onboard ever-smaller and highly flexible aerial platforms, like helicopters or unmanned aerial vehicles (UAVs). In this work, we present the imaging and topographic capabilities of a novel Italian airborne SAR system developed in the frame of cooperation between a public research institute (IREA-CNR) and a private company (Elettra Microwave S.r.l.). The system, which is named AXIS (standing for Airborne X-band Interferometric SAR), is based on FMCW technology and is equipped with a single-pass interferometric layout. In the work we first provide a description of the AXIS system. Then, we describe the acquisition campaign carried out in April 2018, just after the system completion. Finally, we perform an analysis of the radar data acquired during the campaign, by presenting a quantitative assessment of the quality of the SLC (Single Look Complex) SAR images and the interferometric products achievable through the system. The overall analysis aims at providing first reference values for future research and operational activities that will be conducted with this sensor.

Synthetic Aperture Radar (SAR) is an active sensor that can be mounted onboard satellite or airborne platforms for observing of Earth’s surface in any weather condition and even during night [1]. In the last years, it has been shown that the interferometric SAR (InSAR) technique allows [2] generating high quality Digital Elevation Models (DEMs) [1] from spaceborne [3] and airborne [4–7] SAR data. Airborne SAR systems, unlike satellite SAR ones, are particularly suitable for environmental monitoring in case of emergencies due to their capability to maintain very tight revisit times and to acquire data practically without orbital constraints. The contribution of this work fits very nicely within this context. Indeed, in this work, we show the results obtained from the data collected during the acquisition campaigns carried out with the AXIS [5] and MIPS [8] airborne X-band interferometric SAR systems over the Stromboli island (Italy). In particular, starting from multiple single-pass interferometric SAR surveys we present the differences of the generated DEMs with the aim of measuring the topographic changes induced by the eruptive activity over the whole island during the July 2019 – October 2022 time interval. The work is supported by an agreement between IREA-CNR and the Civil Protection Department of Italy.   References 1. Franceschetti, G.; Lanari, R. Synthetic aperture radar processing; 1999; 2. Moreira, A.; Prats-Iraola, P.; Younis, M.; Krieger, G.; Hajnsek, I.; Papathanassiou, K.P. A tutorial on synthetic aperture radar. IEEE Geosci. Remote Sens. Mag. 2013. 3. Rabus, B.; Eineder, M.; Roth, A.; Bamler, R. The shuttle radar topography mission - A new class of digital elevation models acquired by spaceborne radar. ISPRS J. Photogramm. Remote Sens. 2003. 4. Perna, S.; Esposito, C.; Amaral, T.; Berardino, P.; Jackson, G.; Moreira, J.; Pauciullo, A.; Junior, E.V.; Wimmer, C.; Lanari, R. The InSAeS4 airborne X-band interferometric SAR system: A first assessment on its imaging and topographic mapping capabilities. Remote Sens. 2016, 8. 5. Esposito, C.; Natale, A.; Palmese, G.; Berardino, P.; Lanari, R.; Perna, S. On the Capabilities of the Italian Airborne FMCW AXIS InSAR System. Remote Sens. 2020, 12. 6. Pinheiro, M.; Reigber, A.; Scheiber, R.; Prats-Iraola, P.; Moreira, A. Generation of highly accurate DEMs over flat areas by means of dual-frequency and dual-baseline airborne SAR interferometry. IEEE Trans. Geosci. Remote Sens. 2018. 7. Wimmer, C.; Siegmund, R.; Schwäbisch, M.; Moreira, J. Generation of high precision DEMs of the Wadden Sea with airborne interferometric SAR. IEEE Trans. Geosci. Remote Sens. 2000. 8. Natale, A.; Berardino, P.; Esposito, C.; Palmese, G.; Lanari, R.; Perna, S. The New Italian Airborne Multiband Interferometric and Polarimetric SAR (MIPS) System: First Flight Test Results. Int. Geosci. Remote Sens. Symp. 2022, 2022-July, 4506–4509.