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Interferometric radars are widely used sensors for structural health monitoring. They are able to perform dynamic measurements of displacement with sub-millimeter precision. Today, the Ku-band is the most common, due to the spread of commercial systems operating in this band. At the same time, the W-band sensors are gaining ever more interest. Other popular systems work in the X-band. Since the characteristics of the measurements dramatically depend on the operative frequency, it is essential to highlight their differences. For instance, higher frequency allows for high displacement resolution, but it is more subject to phase wrapping and decorrelation effects. In this paper, a direct comparison between radars operating in X, Ku, and W-band for bridge monitoring is carried out. The radars provide frequency-modulated continuous-wave signals. Experimental campaigns were performed both in controlled and realistic scenarios (a stayed bridge). The results of the experiments demonstrate that all the three sensors are suitable for performing dynamic structure monitoring despite their differences. It is worth noting that this comparative analysis has highlighted the role of amplitude variation in phase/displacement measurement. Regarding this point, the three different bands exhibit significant differences. [ABSTRACT FROM AUTHOR]

Ground penetrating radar (GPR) is a powerful non‐destructive investigation tool widely used in archaeology. Its capabilities are greatly enhanced when it is operated in combination with a terrestrial laser scanner. This article reports on the radar investigation of the floor of Palazzo Vecchio's Great Hall. This monumental hall has been decorated by the most prominent artists of Italian Renaissance and it has radically changed at least twice since the 15th century. The aim of this investigation is to find features inside and under the floor that can contribute to a better reconstruction of the history of this monument. The main findings of this prospection have been the detection of a transversal girder not known on the south side of the Great Hall and a hemicycle structure under the floor. Both are probably remains of the works for adapting the hall to be used as the National Parliament of Italy between 1865 and 1870. [ABSTRACT FROM AUTHOR]

In this paper, we report on an experimental activity aimed at investigating the potential of two terrestrial remote-sensing techniques, namely, ground-based SAR (GB SAR) interferometry and terrestrial laser scanning, in order to retrieve snow-depth (SD) measurements in mountainous regions. Terrestrial laser scanning is a more consolidated technique based on the measurement of the optical (near infrared) reflectivity, and it is affected by the surface of the snow layer: a temporal data sequence allows us to estimate the absolute SD variation. Recent use of SAR interferometry to evaluate snow-mass characteristics is based on relating the measured interferometric phase shift to a change in the snow mass. Interferometric GB SAR measurements and terrestrial laser scanner scans were collected together with pointwise conventional measurements of physical snow parameters during the winters of 2005/2006 and 2006/2007. The experiment was carried out in the Wattener Lizum, a high Alpine area at about 2000-m elevation north of the main ridge of the Austrian Alps in Tyrol. Notwithstanding the difficulty of providing both lengthy data record in dry snow conditions and detailed knowledge of the observed snow characteristics, the obtained results confirmed the presence of a clearly measurable interferometric phase variation in relation to the growing height of the snow layer. A comparison of the SD maps obtained through the two techniques shows differences partly due to the different nature of the two observations. Index Terms--Ground-based microwave interferometry, snow depth (SD), terrestrial laser scanner (TLS).

Remote dynamic monitoring of bridges by a high-speed interferometric radar is proposed. The equipment is a continuous-wave step-frequency radar with very fast frequency hopping that is capable of sampling the structure at a rate high enough for transient analysis of motion through phase comparison of successively acquired images. An experimental test carried out on a highway bridge forced by vehicular traffic is presented. Index Terms--Dynamic monitoring, interferometry, radar, remote sensing, structural test.

The alpine village of Lamosano, Belluno, Italy, located near a wide and active landslide, has been seriously threatened by ground instabilities since 1960. In this paper, the results obtained by two different remote-monitoring techniques, synthetic aperature radar interferometry and three-dimensional laser-scanner imaging, planned for Lamosano hazard assessment, are presented. Both techniques compare images taken at different times to map and classify changes that occurred on the imaged scenario. The radar and laser data are gathered at the same dates with about ten-month temporal separation. The displacements measured separately by each of the two techniques highlight a similar sliding motion on the Lamosano village area, providing a good validation to each other and contributing to the definition of the village instability hazard. Index Terms--Digital models, displacement fields, landslide monitoring, synthetic aperture radar (SAR) interferometry, terrestrial laser scanner (TLS).

Ground-based synthetic aperture radar (GB-SAR) interferometry has already been recognized as a powerful tool, complementary or alternative to spaceborne SAR interferometry, for terrain monitoring, and for detecting structural changes in buildings. It has been noted that, in spite of the very short range, compared with the satellite configuration, in GB-SAR measurement the disturbances due to atmospheric effects cannot be neglected either. The analysis of the interferometric phases of very coherent points, called permanent scatterers (PSs), allows the evaluation of the atmospheric disturbance and the possibility of removing it. In this paper, the PS analysis is carried out both on a test site facility and on a real campaign (Citrin Valley, Italy) that provided data with a temporal baseline of about ten months. Index Terms--Atmospheric effect, ground-based synthetic aperture radar (GB-SAR) interferometry, landslide monitoring, permanent scatterer (PS), radar.

The application of ground-based radar iterferometry for landslide monitoring is here analyzed: a case study based on an experimental campaign carried out in Italy in the year 2002 is discussed. Interferometric data obtained from coherent synthetic aperture radar (SAR) images acquired by means of C-band ground-based equipment ave analyzed. The campaign was aimed at retrieving potential terrain movements of a small landslide observed hundreds of meters away. Critical aspects related to spatial and temporal decorrelation ale discussed: the use of optical photogrammetry as a technique for evaluating mechanical stability and correcting geometric distortion is presented. Results also confirmed that the application of ground-based radar interferometry can be attractive and effective if the acquired SAR images maintain an adequate coherence on different dates. Index Terms--Decorrelation, differential interferometry, ground-based synthetic aperture radar, phase stability, synthetic aperture radar (SAR).

Joint time-frequency analysis of penetrating radar response has been tested using simulated and experimental data as a processing tool for detecting stratified features inside a masonry structure. The radar response has been simulated exploiting the formalism of the propagators inside a finite number of dielectric layers. Experimental testing has been carried out by varying the thickness of the hollow space between two walls. Index Terms--Continuous wave step frequency (CW-SF), joint time-frequency analysis (JTFA), microwave, nondestructive testing, radar.

In this paper, the authors propose an innovative survey radar technique based on microwave holographic images for dynamic testing of large structures providing both vibration amplitude pattern and frequency. Theoretical background is provided and experimental results obtained during a dynamic test on a concrete and masonry building are reported. Index Terms--Large structure, microwave, nondestructive testing, radar, remote monitoring.

A miniaturized probe comprising a circular array of optical fibers coupled to a graded-index microlens has been designed for analyzing colloidal solutions by photon correlation spectroscopy (PCS). The system's suitability for PCS measurements was validated by experimental testing performed in bulk solutions and small drops of monodisperse and bimodal test colloidal solutions. Key words: Colloidal solutions, dynamic light scattering, optical fibers, particle size analysis, photon correlation spectroscopy.