# Perspectives on the Structural Health Monitoring of Bridges by Synthetic Aperture Radar  
[PERSON]  
1 Engineering Department, University of L'Aquila [PERSON], Monteluco, Poggio di Roio, 06073 L'Aquila, Italy 14  
[PERSON]  
2 Science and Technology for Transportations Faculty, Universita degli Studi \"[PERSON]\", 1  
[PERSON], 12, 82100 Benevento, Italy; [EMAIL_ADDRESS]  
[PERSON]  
3 Engineering Department, University of Sannio, Universita Degli Studi del Sannio, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON]  
4 Univ-Civita degli Studi, 1  
[PERSON], 12, 82100 Benevento, Italy; 31 Instituto de Ciencias, Universita degli Studi, 1  
We demonstrate that an alternative, and, less expensive and much more portable approach can be used through spaceborne synthetic aperture radar (SAR), thanks to its coherent nature capable to accurately measure several parameters [2; 3; 4; 5]. The benefits of SAR for infrastructure monitoring have been already proved in [6; 7; 8; 9] where Differential Interferometry (DInSAR) is applied, and, when the more complex Persistent Scatterers Interferometry (PS-InSAR) is used [10; 11]. These techniques are able to estimate structure displacement with millimetric precision, along the acquisition time of long series of interferometric SAR observations, although these methods to be accurate need to preserve a good level of coherence in the images within the acquisition time frame [11]. Moreover, acquiring a long temporal series of interferometric SAR observations, as needed for infrastructure monitoring with the PS-InSAR technique, is not a trivial job and, in any case, a minimum number of observations is needed in order to have a reliable phase screen atmosphere estimation [12]. Even more, observing bridges with PS-InSAR is a difficult task because of their large vibrations, this issue is particularly critical when heavy traffic or strong winds are present [13; 14]. All these issues might prejudice the operative SAR products' employment in infrastructure monitoring. On the contrary, we show that measuring infrastructure vibration using a single SAR image, thus ensuring customers to immediately get the result, is possible through micro-motion (m-m) estimation based on modal proprieties analysis, as also recently shown for dam monitoring [15]. In this paper, we give evidence that this approach also well works for a more challenging situation than that represented by bridges (dams are very large infrastructures, which have very extended surfaces and the Doppler perturbations of the received electromagnetic bursts can be more easily detected). In the present work, we consider several examples and demonstrate that different observation geometries do not affect the effectiveness of the method when the selected cases are considered. And this also foresees well for the robustness of the method because of the recurring geometrical conditions inherent the SAR constellation missions that usually are conceived for the application at hand.