Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019)

• Published in: Remote sensing (Basel, Switzerland) Switzerland), 2020-12, Vol.12 (24), p.4011
• Main Authors: Lanari, Riccardo, Reale, Diego, Bonano, Manuela, Verde, Simona, Muhammad, Yasir, Fornaro, Gianfranco, Casu, Francesco, Manunta, Michele
• Format: Article
• Language: English
• Subjects: Accuracy; bridge collapse; Bridge failure; Bridges; Collapse; Datasets; deformation time series; Infrastructure; infrastructures monitoring; InSAR; Interferometry; Investigations; Orbits; Remote sensing; SBAS; Sensors; Spatial discrimination; Spatial resolution; Time series; TomoSAR; Velocity
• ISSN: 2072-4292; 2072-4292
• DOI: 10.3390/rs12244011

We present in this comment a Multi-Temporal SAR Interferometry (MT-InSAR) analysis showing that the results published by Milillo et al. (2019) in the Remote Sensing Journal, presenting the evidence of space geodetic observations relevant to displacements occurring before the collapse of the Morandi Bridge, happened in Genova (Italy) on the 14 August 2018, are questionable. In particular, we focus on the InSAR results obtained by Milillo et al. (2019) by processing the 3 m × 3 m resolution COSMO-SkyMed (CSK) data collected from ascending and descending orbits on the area of interest. These results, thanks to the high spatial resolution and the short revisit time characterizing this multi-orbit SAR dataset, represent the cornerstone of their analysis. The main findings of their study allow Milillo et al. to conclude that the InSAR processing of this COSMO-SkyMed dataset reveals the increased deformation magnitude over time of points located near the strands of the deck next to the collapsed pier, between 12 March 2017 and August 2018. In this comment, we show the results obtained by the IREA-CNR SAR team after processing the same ascending and descending CSK dataset, but by using two alternative and independent processing techniques: the Small BAseline Subset (SBAS) and the Advanced Tomographic SAR (TomoSAR) approaches, respectively. Our analysis shows that, although both the SBAS and the TomoSAR analyses allow achieving denser coherent pixel maps relevant to the Morandi bridge, nothing of the pre-collapse large displacements reported in Milillo et al. (2019) appears in our results, leading us to deeply disagree with the findings of their InSAR analysis.