Massimo Bavusi

Sparse Reconstruction From GPR Data With Applications to Rebar Detection

The problem of detecting and localizing 2-D thin scatterers (i.e., elongated scatterers whose cross sections are small in terms of the probing wavelength) from scattered field measurements is considered. To this end, a linear model that neglects mutual scattering and is based on a distributional representation of the unknown is established. An improved imaging technique based on a minimization algorithm, which takes advantage of the inherent sparseness of the considered ground-penetrating radar scenario, is presented and compared to a classical migration algorithm. The comparison is achieved for both synthetically generated and experimental data collected in realistic conditions under a multimonostatic/multifrequency configuration.

Transport infrastructure surveillance and monitoring by electromagnetic sensing: the ISTIMES project

The ISTIMES project, funded by the European Commission in the frame of a joint Call “ICT and Security” of the Seventh Framework Programme, is presented and preliminary research results are discussed. The main objective of the ISTIMES project is to design, assess and promote an Information and Communication Technologies (ICT)-based system, exploiting distributed and local sensors, for non-destructive electromagnetic monitoring of critical transport infrastructures. The integration of electromagnetic technologies with new ICT information and telecommunications systems enables remotely controlled monitoring and surveillance and real time data imaging of the critical transport infrastructures. The project exploits different non-invasive imaging technologies based on electromagnetic sensing (optic fiber sensors, Synthetic Aperture Radar satellite platform based, hyperspectral spectroscopy, Infrared thermography, Ground Penetrating Radar-, low-frequency geophysical techniques, Ground based systems for displacement monitoring). In this paper, we show the preliminary results arising from the GPR and infrared thermographic measurements carried out on the Musmeci bridge in Potenza, located in a highly seismic area of the Apennine chain (Southern Italy) and representing one of the test beds of the project.

Ground Penetrating Radar in Dam Monitoring: The Test Case of Acerenza (Southern Italy)

Nowadays, dam safety management is gaining great importance since it affects in a crucial way the monitoring and improvement of risky reservoirs, but this topic is very challenging since the dam safety requires long-term and time-continuous monitoring. In this framework, the exploitation of conventional geotechnical investigation methods often requires invasive actions in the inner of the structure to be investigated (destructiveness) and only provides punctual information for small volumes. On the contrary, the application of noninvasive sensing techniques makes it possible to investigate higher volumes without affecting the structure. In this paper we describe the application of GPR for the monitoring and diagnostics of one of the largest dams in the Basilicata region (Southern Italy). The investigation aims at detecting and localizing underground sandstone banks that are potential ways of flow of water below the dam. The manageability and the noninvasiveness of GPR have resulted in particularly suitable for this kind of application because the versatility of this geophysical method allows to investigate large areas with a good spatial resolution giving the possibility to detect the presence of inhomogeneities in the subsoil below the dam.

Structural monitoring via microwave tomography-enhanced GPR: the Montagnole test site

Structural integrity assessment and monitoring of infrastructures are key factors to prevent and manage crisis events (natural disasters, terrorist attacks and so on) and ensure urban safety. This necessity motivates huge interest towards design, optimization and integration of non-invasive remote and in situ diagnostic techniques. In this framework, ground penetrating radar (GPR) is a well-assessed instrumentation, which allows one to attain information on the inner status of man-made structures while avoiding invasive tests. However, despite its potential, a more widespread use of GPR is actually affected by the difficulties in providing highly informative and easily interpretable images as an outcome of the overall diagnostics procedure. This drawback can be mitigated thanks to the use of microwave tomography (MT) as a data processing tool able to enhance the achievable reconstruction capabilities, and several proofs of its effectiveness have been already shown. In this paper, the potential of the MT approach is investigated in the framework of structural monitoring by an experiment carried out in the Montagnole test site in the French Alps, where the progressive damage of a one-scale concrete beam has been monitored thanks to the integration of several electromagnetic sensing techniques. In this framework, the capability of the MT-enhanced GPR strategy is examined with respect to the possibility of providing information about the damage of the rebar grid of the beam.

A new combined wavelet methodology: implementation to GPR and ERT data obtained in the Montagnole experiment

Ground penetrating radar (GPR) and electric resistivity tomography (ERT) are well assessed and accurate geophysical methods for the investigation of subsurface geological sections. In this paper, we present the joint exploitation of these methods at the Montagnole (French Alps) experimental site with the final aim to study and monitor effects of possible catastrophic rockslides in transport infrastructures. The overall goal of the joint GPR–ERT deployment considered here is the careful monitoring of the subsurface structure before and after a series of high energetic mechanical impacts at ground level. It is known that factors such as the ambiguity of geophysical field examination, the complexity of geological scenarios and the low signal-to-noise ratio affect the possibility of building reliable physical–geological models of subsurface structure. Here, we applied to the GPR and ERT methods at the Montagnole site, recent advances in wavelet theory and data mining. The wavelet approach was specifically used to obtain enhanced images (e.g. coherence portraits) resulting from the integration of the different geophysical fields. This methodology, based on the matching pursuit combined with wavelet packet dictionaries, permitted us to extract desired signals under different physical–geological conditions, even in the presence of strongly noised data. Tools such as complex wavelets employed for the coherence portraits, and combined GPR–ERT coherency orientation angle, to name a few, enable non-conventional operations of integration and correlation in subsurface geophysics to be performed. The estimation of the above-mentioned parameters proved useful not only for location of buried inhomogeneities but also for a rough estimation of their electromagnetic and related properties. Therefore, the combination of the above approaches has allowed us to set up a novel methodology, which may enhance the reliability and confidence of each separate geophysical method and their integration.

A Comparison between Two GPR Data Processing Techniques for Fracture Detection and Characterization

The abstract deals with the fracture detection in civil engineering via Ground Penetrating Radar. In particular, we present the comparison between two data processing techniques. The first one is a conventional technique while the second one is a novel m

Groundwater Monitoring and Control by Using Electromagnetic Sensing Techniques

Groundwater resources, which are exposed to overexploitation and pollution at regional and local levels, may take benefit from fast, nonintrusive, and inexpensive monitoring methods based on electromagnetic techniques. In fact, the available technologies can help to improve management and protection of the aquifers. This chapter deals with the role of electromagnetic sensing techniques in water monitoring with a specific focus to pollution surveys in groundwater bodies. Being sensitive to the presence of water in the subsoil and its electrical conductivity, which in turn depends on the ionic content, the electromagnetic sensing techniques are useful tools for groundwater identification and soil quality assessment. In fact, these sensing techniques offer advantages such as quickness, nonintrusivity, and the possibility of investigating large areas at reasonable costs. However, the appropriate use of these techniques implies an adequate knowledge of their working principles as well as of their on field application procedures, which mainly depend on the survey aim and the geological and logistic conditions of the site. This chapter also discusses the uncertainty in the interpretation of results, which is due to the fact that the electromagnetic sensing techniques are based on indirect inspections. Several strategies can be exploited to reduce ambiguity of results, such as the integration of different electromagnetic techniques and the comparison between field data and those provided by laboratory experiments. These issues are herein addressed through practical examples concerning two study cases, one referred to a site located in Serbia-Herzegovina and one located in Italy. In particular, we illustrate the physical concepts, the operative aspects, the data processing, and the integration of results concerning the following measurement techniques: electrical resistivity tomography (ERT), ground-penetrating radar (GPR), time-domain-induced polarization (time domain IP), and self-potential method (SP). The two study cases concerns an industrial site and a large waste dump structure. These sites represent specific examples of soil monitoring and have been selected in order to evaluate the performance of the proposed techniques. For each site, we provide a description of the survey results accounting for geological evidences, logistic constraints, and physical limitation of the used techniques. Finally, we highlight the advantages offered by a cooperative use of different techniques and suggest strategies to overcome intrinsic limitations of each one of the considered survey methods.

Electromagnetic Sensing Techniques for Non-Destructive Diagnosis of Civil Engineering Structures

Health Assessment Methods (HAM) and Structural Health Monitoring (SHM) aim to improve the standard of knowledge regarding the safety and maintenance of structures and infrastructure acquiring information about geometrical, mechanical and dynamical characteristics of structures. In earthquake-prone areas, this activity has the double aim of assessing the buildings structural integrity and extracting information regarding their response during a seismic event in order to define appropriate activities for risk mitigation. A number of factors afflict buildings and infrastructure safety in seismic areas:  Outdated codes of practice: a significant number of highly urbanized areas are present globally, where a high percentage of structures have been designed and erected considering only gravity loading.  The age of the structures and the real in-situ performance of construction material significantly affect their overall behaviour.  Structural deficiencies such as poor material qualities and/or degradation of structural materials (rust, spalling etc.), inadequate construction detailing, low levels of ductility, brittle collapse mechanisms. The seismic assessment of structures is performed in terms of the estimation of the earthquake intensity that would lead to a certain damage condition and/or collapse. The assessment of the seismic vulnerability of existing buildings is generally based on the knowledge of building characteristics and through a complex analysis of the possible collapse mechanisms in order to identify the most probable failure for the given structure (as example: Ansari, 2005; Douglas, 2007; Moustafa et al., 2010). The methodological approach for the evaluation of a structure resistance is represented in Figure 1 where structural knowledge obtained through a series of test assessments is needed in order to define vulnerability and thus design suitable retrofit strategies.

GPR and ERT combined analysis on the basis of advanced wavelet methodology: The Montagnole testing area

Ground Penetrating Radar (GPR) and Electric Resistivity Tomography (ERT) are well assessed and accurate geophysical methods for the investigation of subsurface geological sections. In this paper, we present the joint exploitation of these methods al the Montagnole (French Alps) experimental site with the final aim to study and monitor effects of possible catastrophic rockslides in transport infrastructures. It is known that factors as the ambiguity of geophysical field examination, the complexity of geological scenarios, and the low signal-to-noise ratio affect the possibility to build reliable physical-geological models of the investigated subsurface structure. Here, we applied for the GPR and ERT methods at Montagnole site, the recent advances in the wavelet theory and data mining. Wavelet approach was specifically used to achieve enhanced (e.g., coherence portraits) images resulting from the integration of the different geophysical fields. This methodology based on the matching pursuit combined with wavelet packet dictionaries permitted us to extract desired signals in different physical-geological conditions, even in presence of strongly noised data. Such tools as complex wavelets were employed to the coherence portraits, combined GPR-ERT coherency orientation angle, to name a few, enable performing non-conventional operations of integration and correlation in subsurface geophysics. The estimation of the above mentioned parameters proved useful not only for location of buried inhomogeneties but also for a rough estimation of their electromagnetic and related properties. Therefore, the combination of the above approaches has allowed to set-up a novel methodology, which may enhance reliability and confidence of each separate geophysical method and their integration.

Electromagnetic Methods and Sensors for Water Monitoring

This paper deals with a brief presentation of non or minimally invasive techniques of interest for water security and monitoring applications, based on electromagnetic sensing. The techniques are presented according to the frequency range and to the degrees of novelty for the specific applicative context. For each technique, we briefly sketch the basic theory and the general and specific interest for the water monitoring. Besides well assessed techniques such as Electrical Resistivity, Electromagnetic Induction, Ground Penetrating Radar and Time Domain Reflectometry, Self Potential and Magnetometry, we give a short presentation of techniques of recent interest, some of them still in course of development, such as: Hyperspectral and TeraHertz Imaging.