This work presents a methodology to monitor the dynamic behaviour of tall metallic towers based on ground-based radar interferometry, and apply it to the case of telecommunication towers. Ground-based radar displacement measurements of metallic towers are acquired without installing any Corner Reflector (CR) on the structure. Each structural element of the tower is identified based on its range distance with respect to the radar. The interferometric processing of a time series of radar profiles is used to measure the vibration frequencies of each structural element and estimate the amplitude of its oscillation. A methodology is described to visualize the results and provide a useful tool for the real-time analysis of the dynamic behaviour of metallic towers.without the need to access the structure to install any device. Furthermore, an optimal technique should be easy to be included in a monitoring protocol of structural dynamic characteristics for the quick periodic inspection of towers and trellises.Ground-based radar systems have been proposed to monitor infrastructures and as a supporting tool in natural and man-made disasters [3][4][5][6]. For example, the Ground-Based SAR (GB-SAR) technique has been used to monitor dams and piers, merging ground-based radar measurements with those provided by traditional geodetic techniques [7][8][9].The characterization of the dynamic behavior of bridges by means of a ground-based radar, laser beam and laser scanning systems are presented in [10] and [11,12], respectively. The knowledge acquired in the case of the dynamic characterization of bridges can also be useful to study the structural health of telecommunication towers and power line trellises. We chose to use a ground-based radar to monitor the metallic towers. Among the useful advantages of this technique, we can cite: (a) the capability to provide information in any weather conditions and during night operations, and (b) the possibility to perform measurements for any distance between the tower and the radar, within a maximum range of about four kilometers. All of these properties are important for the inspection of the structural health of towers, and in cases of emergency. In particular, the larger maximum working range distance of the radar is extremely useful in the case of towers located in urban areas where it could be difficult to find places not affected by ambient sources of vibration, such as traffic jams. A ground-based radar can provide a full-scale measurement of towers subject to ambient vibrations as required in [1]. Ground-Based Real Aperture Radar (GB-RAR) measurements of vibration frequencies have been validated by accelerometers in many papers (e.g., [13,14]). A methodology to visualize the vibration spectra of each structural element of an infrastructure, imaged with a spatial resolution of 0.75 m in range, has been described in [15].In this work, we present an application of ground-based radar interferometry to measure the vibration frequencies and displacements of telecommunications towers. ...
Tangible cultural heritage, historical buildings and bridges have an important cultural significance and economic value within the tourism industry and the identity of local communities. The preservation and the assessment of their structural health are important issues which call for multidisciplinary teams and non-invasive monitoring techniques due the uniqueness and historical values of these man-made structures. Numerical models used to study the structural behavior of these historical buildings and bridges under different adverse conditions (e.g. intense traffic flow, natural hazard events, chemical pollution or simply aging) can benefit from accurate measurements of mechanical properties such as displacements and vibration frequencies, both bringing information about the static and dynamical behavior of such historical constructions. This work presents some results of structural monitoring of man-made structures by Ground-based Synthetic Aperture Radar (GBSAR) interferometry techniques. A ku-band GBSAR interferometer is used to derive displacement maps of the monitored target, with a sub-millimeter precisions. Furthermore, GBSAR interferometry is used to measure vibration frequencies of vertical and horizontal structures, such bell towers, towers, bridges and historical walls. The main advantage of this technique is its capability to operate in any weather and sun-illumination condition, in a truly Non-Destructive Monitoring (NDM) approach, i.e. without installing any reflector on the observed target.
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