## 1 Introduction
In this paper, we focus on the above described first level of the observational chain, which combines the Differential Synthetic Aperture Radar (SAR) interferometry (DInSAR) measurements and accelerometer based data for the monitoring of strategic infrastructure located in Rome; this activity falls within the WP6 \"Structural Health Monitoring and Satellite Data\" 2019-21 Reluis Project developed under the framework of the Italian Civil Protection Department agreement. In this first stage of observation, the DInSAR measurements provide information about the long-term deformation status both of the structure and of the surrounding soil. This twofold point of views has been introduced in order to tentatively distinguish between generalized deformation trend induced by independent large scale geological processes such as, for example, subsidence or landslide affecting the area, and localized deformation trends mainly related to the structure or to the soil-structure interaction. The vibrational-based data (accelerometric and/or velocimetric data) provide information about the frequencies of structural vibration and their possible variation over time. Several studies demonstrate the possibility to use changing in modal characteristics of a monitored structure to detect damages and criticalities on both structural and non-structural components, see [7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23]). These in situ data have been provided by the Italian Civil Protection Department (DPC), through the Seismic Observatory of Structures (OSS) [24], a network of permanent seismic monitoring systems installed on public buildings, bridges and dams [25]. Moreover, the in situ observations have been completed with a visual survey of the building and several ambient vibration measurements, which have been performed on October 2020. The overall analysis has the aim of evaluating the condition of the structure, assess any already existing or potential defects and identify possible anomalies. The paper is organized as follows: Section 2 briefly summarizes the main aspects and applications of the exploited DInSAR technique; in Section 3 the case study is illustrated; Section 4 reports the main geological characteristics of the investigated area where the case study is located; in Section 5 data processing and results are displayed; Section 6 provides a discussion about the advantages and limits of different methods. Section 7 reports the main findings together with the conclusions. Differential Synthetic Aperture Radar Interferometry (DInSAR) for Structural Deformation Monitoring  
Remote sensing can provide valuable information in a large variety of natural and anthropic hazard scenarios thanks to its synoptic capability, for instance when a seismic event occurs in remote regions, or the main communication systems are damaged [26]. In this framework, the Synthetic Aperture Radar (SAR) satellite sensors have been widely used in the last decades for analyzing the surface displacements, uplifts and subsidence phenomena caused by earthquakes [27; 28; 29; 30], since they provide high spatial resolution images relevant to very large areas on the Earth's surface, with all weather and continuous (night and day) imaging capabilities. Research outputs have been already published regarding post-seismic building damage assessment performed by combining pre- and post-seismic images [31; 32; 33], using SAR simulations or combining radar and optical remote-sensing data [26; 34]. The satellite DInSAR technique is one of the most innovative methodologies for ground and structures displacement monitoring in urban areas. DInSAR is based on the exploitation of the phase difference (i.e., interferogram) between two temporally separated SAR images that, following the phase unwrapping operation [35; 36], permits information on the detected displacements to be retrieved, projected along the radar sensor Line of Sight (LOS), that occurred between the two acquisition times, with centimeter accuracy [30].