Abstract
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.
Highlights
As RaemfionteaSlenps.o20in20t,12it, xisFOoRnPcEeERagREaVinIEWworth remarking that the results achieved by exploit1i1nogf 1t7he two independent Small BAseline Subset (SBAS) and Tomographic SAR (TomoSAR) approaches are in very good agreement, regardless of the reference pixels selection, confirming the robustness of the applied MT-InSAR processing approaches
It is once again worth remarking that the results achieved by exploiting the two independent SBAS and TomoSAR approaches are in very good agreement, regardless of the reference pixels selection, confirming the robustness of the applied MT-InSAR processing approaches
This is quite evident by the analysis of the deformation time series and related mean velocities in correspondence to the Morandi bridge obtained by exploiting both ascending and descending data and both the SBAS and the TomoSAR MT-InSAR approaches
Summary
On the 14 August 2018, the Polcevera viaduct—known as the Morandi bridge—in the city of Genova (Italy), which connects the eastern and western sides of the Genova metropolitan area and represents the main highway to link Southern France and Northern Italy, suffered the collapse of a section of the deck approximately 240 m long, adjacent to pier 9, close to the Polcevera river, causing the death of 43 people, and leaving 11 injured [1]. The results presented in [2] allow the Authors to conclude that the CSK-based InSAR analysis reveals an increased deformation magnitude over time in correspondence to points located near the strands of the deck next to the collapsed pier, between 12 March 2017 and the beginning of August 2018 These findings clearly disagree with those of the above-mentioned expeditious analyses carried out immediately after the bridge collapse. In the presented study, we reprocessed the overall ascending and descending CSK dataset analyzed in [2] by exploiting two independent SAR processing techniques: the Small BAseline Subset (SBAS) [5,6,7] and the Advanced Tomographic SAR (TomoSAR) [8,9] approaches, respectively These two methods are nowadays well-established tools for the investigation of the temporal evolution of displacements affecting buildings and infrastructures [10,11,12,13,14,15,16,17,18,19,20]. Our findings, resulting from the independent processing of each dataset, lead us to conclude that we do not find any evidence of the pre-collapse displacements reported in [2] in pixels located near the strands of the deck next to the collapsed pier
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