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

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## Abstract

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## 1. Introduction

## 2. Exploited Data and Multi-Temporal SAR Techniques

#### 2.1. CSK Dataset

#### 2.2. The SBAS Technique

#### 2.3. The TomoSAR Technique

## 3. Results

## 4. Discussion and Conclusions

## Supplementary Materials

## Author Contributions

## Funding

## Acknowledgments

## Conflicts of Interest

## References

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**Figure 1.**Representation of the two exploited COSMO-SkyMed (CSK) frames acquired from ascending (black rectangle) and descending (red rectangle) orbits, superimposed on a Google Earth optical image. Note that the white rectangle falling within the two frames represents the area of interest surrounding the Polcevera viaduct close to the Morandi bridge.

**Figure 2.**SAR data representation in the temporal/perpendicular baseline plane for the two CSK datasets relevant to the area of interest. The black triangles and the red diamonds represent the ascending and descending acquisitions, respectively. The reference (master) images selected for the processing of the ascending and descending CSK datasets, relevant to the 29 October 2014 and to the 3 February 2015 acquisitions, respectively, are identified by the arrows.

**Figure 3.**Mean deformation velocity maps over the area of interest for (

**a**) Small BAseline Subset (SBAS) and (

**b**) TomoSAR processing results achieved for the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Colormap is set according to the estimated velocity with the convention that negative values correspond to departure from the sensor along the LOS. Reference pixels for SBAS and TomoSAR processing are located at [44.4130°, 8.8879°] and [44.4160°, 8.8738°], respectively, which are in stable areas far away from the bridge.

**Figure 4.**Highlight on the coherent pixels located within the yellow frame, corresponding to the northern roadway, for (

**a**) SBAS and (

**b**) TomoSAR processing results achieved for the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Colormap is set according to the estimated velocity with the convention that negative values correspond to departure from the sensor along the Line of Sight (LOS). The white graduated axis represents the longitudinal coordinate of the yellow rectangle whose origin is set at the southern/eastern end of the bridge.

**Figure 5.**Plots of the estimated height of the coherent pixels located within the yellow rectangle in Figure 4 for (

**a**) SBAS and (

**b**) TomoSAR results achieved for the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Red and black diamonds correspond to measurement points located on the roadway, pillars and cables and at the ground level, respectively. Horizontal axis corresponds to the longitudinal distance from the origin of the yellow rectangle located at its southern/eastern end, as reported by the white graduated scale in Figure 4.

**Figure 6.**Plots of the estimated deformation mean velocity of the coherent pixels located at the northern roadway level within the yellow rectangle in Figure 4 for the (

**a**) SBAS and (

**b**) TomoSAR processing results achieved for the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Horizontal axis corresponds to the longitudinal distance from the origin of the yellow rectangle located at its southern/eastern end, as reported by the white graduated scale in Figure 4.

**Figure 7.**Zoom of Figure 4 in the area of interest related to the collapsed pillar, (

**a**) SBAS and (

**b**) TomoSAR processing results over the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset.

**Figure 8.**Plots of the estimated deformation time series for the coherent pixels in the area of interest related to the collapsed pillar provided in Figure 7 for (

**a**) SBAS and (

**b**) TomoSAR results relevant to the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results for the descending dataset.

**Figure 9.**Highlight on the measurement points located within the red frame, corresponding to the southern roadway for (

**a**) SBAS and (

**b**) TomoSAR processing results related to the ascending dataset, (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Colormap is set according to the estimated velocity with the convention that negative values correspond to departure from the sensor along the LOS. The white graduated axis represents the longitudinal coordinate of the red rectangle whose origin is set at the southern/eastern end of the bridge.

**Figure 10.**Plots of the estimated height of the coherent pixels located within the red rectangle in Figure 9 for the (

**a**) SBAS and (

**b**) TomoSAR processing results related to the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. Red and black squares correspond to measurement points located at the roadway, pillars and cables and at the ground level, respectively. Horizontal axis corresponds to the longitudinal distance from the origin of the red rectangle located at its southern/eastern end, as reported by the white graduated scale in Figure 9.

**Figure 11.**Plots of the estimated mean deformation velocity of the coherent pixels located at the southern roadway level within the red rectangle in Figure 9 for (

**a**) SBAS and (

**b**) TomoSAR processing results of the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results relevant to the descending dataset. The horizontal axis corresponds to the longitudinal distance from the origin of the red rectangle located at its southern/eastern end, as reported by the white graduated scale in Figure 9.

**Figure 12.**Zoom of Figure 9 in the area of interest related to the collapsed pillar, (

**a**) SBAS and (

**b**) TomoSAR processing results over the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR processing results related to the Descending dataset.

**Figure 13.**Plots of the estimated deformation time series for the coherent pixels in the area of interest of the collapsed pillar provided in Figure 12 for the (

**a**) SBAS and (

**b**) TomoSAR results achieved for the ascending dataset, and (

**c**) SBAS and (

**d**) TomoSAR results related to the descending dataset.

Ascending | Descending | |
---|---|---|

Wavelength | ~3,1 cm | |

Acquisition mode | H-IMAGE | |

Average look angle | ~34° | ~27° |

Spatial resolution of the interferometric data | ~3 m × 3 m | |

Beam-ID | H4-05 | H4-01 |

Time interval | 23 February 2011–5 August 2018 | 7 January 2011–6 August 2018 |

Number of acquisitions | 132 | 134 |

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## Share and Cite

**MDPI and ACS Style**

Lanari, R.; Reale, D.; Bonano, M.; Verde, S.; Muhammad, Y.; Fornaro, G.; Casu, F.; Manunta, M. Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019). *Remote Sens.* **2020**, *12*, 4011.
https://doi.org/10.3390/rs12244011

**AMA Style**

Lanari R, Reale D, Bonano M, Verde S, Muhammad Y, Fornaro G, Casu F, Manunta M. Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019). *Remote Sensing*. 2020; 12(24):4011.
https://doi.org/10.3390/rs12244011

**Chicago/Turabian Style**

Lanari, Riccardo, Diego Reale, Manuela Bonano, Simona Verde, Yasir Muhammad, Gianfranco Fornaro, Francesco Casu, and Michele Manunta. 2020. "Comment on “Pre-Collapse Space Geodetic Observations of Critical Infrastructure: The Morandi Bridge, Genoa, Italy” by Milillo et al. (2019)" *Remote Sensing* 12, no. 24: 4011.
https://doi.org/10.3390/rs12244011