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This paper investigates the performance of an advanced imaging procedure for ground penetrating radar (GPR) operating in contactless configuration, i.e., when data are collected at variable distances from the air-soil interface. A data processing procedure is presented, based on an advanced implementation of a microwave tomographic approach. This improved version, recently proposed by the authors, is able of accounting for the near-field distribution generated by a directional transmitting antenna. The effectiveness of the procedure is shown by processing numerical data, which are obtained by suitably implementing a realistic system on a full-wave commercial simulator. Metallic canonical objects are considered to compare the reconstruction capabilities of the proposed algorithm with respect to more conventional procedures, as well as to assess the role of the antenna distance from the air-soil interface. [ABSTRACT FROM AUTHOR]

The imaging capabilities achieved from a ground-penetrating radar (GPR) system based on a contactless differential measurement configuration and from a microwave tomographic approach are investigated. The system is made up of two receiving antennas located at different heights and placed symmetrically with respect to the transmitting antenna. The data, obtained as the difference between the signals measured by the two receivers, are processed by means of a microwave tomographic approach, which is based on a linear model of the electromagnetic scattering and is specifically designed for the differential GPR system. The achievable reconstruction capabilities are theoretically investigated and their dependence on the offset between the receiving antennas is taken into account in order to provide hints about the preferable offset. The theoretical analysis corroborates that, in the case at hand, the reconstructed images are affected by a spatial filtering effect and the retrievable spectral content is reduced by “hyperbolas of zeroes,” whose occurrence increases with the spatial offset between the two receiving antennas. The effectiveness of the proposed GPR system and of the theoretical analysis is assessed against both synthetic and experimental data. [ABSTRACT FROM PUBLISHER]

The monitoring of the structural integrity of critical transport infrastructures is extremely important in order to prevent accidents, disasters and ensure urban safety. For this reason, several remote and in situ nondestructive electromagnetic technologies have been exploited as diagnostic tools, from which it is possible to obtain information and images of the infrastructure inner status at different spatial and temporal scales. In this framework, this paper deals with holographic ground-penetrating radar tomographic imaging, used as an in situ diagnostic tool to provide high-resolution images of shallowly buried metallic and dielectric objects. As a matter of fact, the need of integrating information gathered at different scales for a global assessment of the structure health makes the (local and high resolution) image obtained by means of this technique particularly valuable. In particular, we consider the Rascan-4/4000 radar system coupled with a tomographic imaging approach specifically tailored to process holographic data, which is adopted to improve the achievable spatial resolution. A proof of concept of the reconstruction capabilities is given against laboratory data. Moreover, on-field examples in the framework of concrete structures monitoring are shown by processing data collected at the Musmeci bridge in Potenza, Italy. [ABSTRACT FROM AUTHOR]

We discuss the applicability of the Linear Sampling Method (LSM) to GPR surveys carried out using array-based configurations. Since the images achieved via LSM are known to get worse when using a small number of antennas and a limited aperture, we introduce an analytic tool to foresee the expected LSM performance for a fixed array size and number of antennas. Notably, such a tool allows us to support (and appraise) the adoption of LSM to data collected with short arrays moved above the investigated domain, which is the configuration most viable in applications. [ABSTRACT FROM AUTHOR]

In the recent years, structural monitoring of large infrastructures (buildings, dams, bridges) or more generally man-made structures has raised an increased attention due to the growing interest about safety and security issues and risk assessment through early detection. In this framework, aim of the paper is to introduce a new integrated approach which combines two sensing techniques acting on different spatial and temporal scales. The first one is a distributed optic fiber sensor based on the Brillouin scattering phenomenon, which allows a spatially and temporally continuous monitoring of the structure with a "low" spatial resolution (meter). The second technique is based on the use of Ground Penetrating Radar (GPR), which can provide detailed images of the inner status of the structure (with a spatial resolution less then tens centimetres), but does not allow a temporal continuous monitoring. The paper describes the features of these two techniques and provides experimental results concerning preliminary test cases. [ABSTRACT FROM AUTHOR]

This paper presents a case study regarding the cooperative use of non-destructive contactless diagnostic investigations as a tool to aid and assist the degradation evaluation of an iconic Roman masonry bridge: Ponte Lucano in Tivoli, Italy. Specifically, unmanned aerial photogrammetric surveys are considered to perform detailed visual inspections and obtain a geometrical 3D model; infrared thermography analyses are carried out to characterize the thermal surface map of the structure detecting anomalies related to material degradation, such as the presence of humidity; ground penetrating radar investigations are performed to improve knowledge of the bridge subsurface structure. The results of the analyses demonstrate that the integration of mentioned diagnostic tools provides information regarding the degradation state of the stones and its causes, as well as regarding the evolution of the structure from its construction up to the present configurations. • A multi-sensing approach is proposed for enhancing structural and material degradation evaluation. • UAV photogrammetric survey was used for visual inspection and 3D model reconstruction. • Infrared thermography allowed to identify ongoing material pathologies. • Ground Penetrating Radar was used for subsurface investigations. • The methodology was applied to an ancient Roman masonry bridge. [ABSTRACT FROM AUTHOR]