# Perspectives on the Structural Health Monitoring of Bridges by Synthetic Aperture Radar
## 3 Analyses of Structural Integrity of Bridges from SAR  
The experimental results are obtained by processing series of SAR data observed by the Italian CSK satellite constellation. The analysis focuses on the detection, localization, and quantification of vibration trends over five study cases concerning sensible bridges and highway overpasses. In order to achieve this objective, the vibration maps extracted from SAR observations are compared with each other to identify critical points within the structure of the bridge. This is mainly due to the fact that localized areas of fatigue on the bridge structure, such as corrosive phenomena or cracks can generate energy singularities clearly visible on the vibration maps estimated using the proposed technique.  
The main characteristics of the SAR acquisition are summarized in Table 1, whereas the detailed list of the performed experiments and data used are shown in Table 2. In particular, the following five cases have been studied:  
(1) **\"Ponte dell'Industria\"** is a bridge crossing the Tiber River when it flows through the city of Rome (in the analysis, we consider two opposite geometries, namely, right ascending and right descending, to compare different acquisitions over the same bridge and to prove the repeatability of the procedure);  
(2) **\"Celico\"** bridge is located in Calabria, a region in southern Italy (it consists of three main spans and two semi-arches);  
(3) **\"Bisantis\"** bridge is also located in Calabria (both Celico and Bisantis are made of pre-compressed concrete that are very old and still in operation today);  
(4) **\"Italia\"** of the \"SS-119\", an Italian motorway, is also located in Calabria region (the vibration anomalies are analysed);  
(5) the last case study investigates the vibration analysis of the the **\"Morandi\"** bridge, which collapsed during a strong storm on 14 August 2018 (the \"Morandi\" bridge crossed the city of Genoa and its collapse caused 43 victims, and, thanks to the proposed method, many critical points have been found on the collapsed stall in a period before the tragic event).  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**SAR Parameter** & **Value** \\ \hline Chirp bandwidth & 80 MHz \\ PRF & 2.5 kHz \\ PRT & 0.23 ms \\ Antenna length & 6 m \\ Type of acquisition & Stripmap \\ Polarization & HH \\ Acquisition duration & 5 s \\ Platform velocity & 7 km/s \\ Observation height & 650,000 m \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of the SAR acquisitions.  
\begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Case Study** & **Bridge Name** & **Processing** & **Coordinates (WGS-80)** & **Time of obs.** & **Number of obs.** \\ \hline
1 & Industria & Modal & \(41^{\circ}52^{\prime}18.96^{\prime\prime}\)N & 8 March–13 March 2018 & 2 \\  & & \(12^{\circ}28^{\prime}19.89^{\prime\prime}\)E & & \\
2 & Celico & Modal & \(39^{\circ}18^{\prime}49.84^{\prime\prime}\)N & 21 March 2018 & 1 \\  & & \(16^{\circ}20^{\prime}64.89^{\prime\prime}\)E & & \\
3 & Bisantis & Modal & \(38^{\circ}54^{\prime}31.41^{\prime\prime}\)N & 12 April 2018 & 1 \\  & & \(16^{\circ}35^{\prime}24.15^{\prime\prime}\)E & & \\
4 & Italia & Modal & \(38^{\circ}54^{\prime}6.11^{\prime\prime}\)N & 14 March 2018 & 1 \\
5 & Morandi & Modal & \(16^{\circ}34^{\prime}35.15^{\prime\prime}\)N & 21 January 2016–5 July 2018 & 2 \\  & & \(08^{\circ}53^{\prime}18.15^{\prime\prime}\)E & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: List of data used for experimental results.