A. Di Matteo

GPR Response From Buried Pipes: Measurement on Field Site and Tomographic Reconstructions

The identification of the physical nature of an object or target causing a ground-penetrating radar (GPR) anomaly, as well as the estimation of a targets dimensions and geometry, is rather challenging. To improve target identification, basic studies are still required, and they can be addressed primarily using a laboratory- or field-based physical model. The field model (test site) is usually expensive and difficult to build, but it provides data for controlled target properties and geometry from a natural environment that are essential for testing processing techniques. In this paper, we present the results from a field experiment where GPR data were collected on plastic and metallic pipes. The main objective is the comparison of the classical migration technique with a microwave tomography approach for reconstructing the geometrical target properties. The use of the microwave tomography approach will allow us to obtain more focused and stable images of the buried objects compared to the ones obtained using classical migration techniques.

Electromagnetic propagation features of ground penetrating radars for the exploration of martian subsurface

In this work, the effects of magnetic inclusions in a Mars-like soil are considered with reference to the electromagnetic propagation features of ground-penetrating radars (GPRs). Low-frequency and time-domain techniques, using L-C-R meters and TDR instruments, respectively, are implemented in laboratory experimental set-ups in order to evaluate complex permittivity and permeability and wave velocity for different scenarios of a dielectric background medium (silica) with magnetic inclusions (magnetite). Attenuation and maximum detection ranges have also been evaluated by taking into account a realistic GPR environment, which includes the transmitting/receiving antenna performance and the complex structure of the subsurface. The analysis and the interpretation of these results shed new light on the significant influence of magnetic inclusions on the performance of Martian orbiting and rover-driven GPRs.

Design and construction of a large test site to characterize the GPR response in the vadose zone

In this work Ground Penetrating Radar (GPR) and Time Domain Reflectometry (TDR) measurements are carried out on a test-site. The test site consists of a pit filled with gravel and sand in which a pipe system for water inflow is buried. The data are collected under different water charge conditions and the water level is monitored by piezometers. TDR measurements are performed at various depths using a multilevel probe system. GPR measurements are performed by using the single-offset reflection method with a system equipped with 250 MHz and 500 MHz antennas. The results pertaining to the water table depth estimations, obtained by calibrating time GPR section with TDR velocity data, have shown a good agreement with the piezometric responses.

GPR application to the structural control of historical buildings: two case studies in Rome, Italy2009-06

Preservation of historical buildings requires particular care, as any intervention must not alter or damage the style, structure or contents of the edifice. In order to properly plan the restoration of a building, non-destructive techniques can be used extensively to detect structural elements and weaknesses. Ground-penetrating radar (GPR) is particularly well adapted to this type of work, as the method is non-invasive, rapid and provides high-resolution images of contrasting subsurface materials. In the present work we show the successful application of the GPR technique to the investigation of two historical buildings that differ in age, structure and geometry. The first case is the GPR detection of fractures and internal lesions in the architrave of the Porticus Octaviae, a partially restored Roman building. The second case uses GPR in the important Zuccari Palace to determine the internal structure above vaulted ceilings that host a series of 16 th century frescos. Both buildings are located in downtown Rome, Italy. These examples show that GPR can give detailed, non-invasive data that describe the state of conservation of historical buildings. In particular, this technique can produce fundamental information for the restorers (e.g., location, dimension and geometry of the structural lesions) that will help them develop the best possible protection plan, retrieving quantitative information about the location and the dimension of the lesions as well as the thickness of the different layers.

Electromagnetic Parameters of Dielectric and Magnetic Mixtures Evaluated by Time-Domain Reflectometry

The frequency-domain analysis of time-domain reflectometry (TDR) data can be used to evaluate the electromagnetic (EM) parameters of a sample under test. The goal of this letter was to use TDR to determine EM parameters, assumed to be frequency independent, for various magnetite/glass-beads mixtures. The EM parameters are, in turn, used to determine the velocity and attenuation of propagating waves. The latter quantity is also obtained through the TDR voltage method. Velocities decrease, and attenuations increase with increasing magnetite content. The measurements of the present work are compared with the velocities and attenuations reported in the literature (measured via the network analyzer (NA) and LCR meter techniques). The velocities calculated using the various methods are in good agreement. In contrast, the attenuations determined by fitting the TDR data only agree with the NA measurements at high frequencies (450 MHz), while those obtained by the TDR voltage method match the low-frequency attenuations determined through the LCR meter. The reasons for these behaviors are discussed, and the need for precise handling of the TDR data is emphasized. The TDR fit procedure is recommended to obtain reliable EM parameters of materials.

On the attenuation factor measurements of glass beads/magnetite mixtures and on the effective frequency evaluation by time domain reflectometry

AhtracrSamples with different percentages (5-25%) of magnetite and different grains size ranges are analyzed by Time Domain Reflectometry (TDR) for deriving the bandwidth and the attenuation factor a . The spectral content of the signal changes as function of the material investigated. Indeed, the bandwidths narrow with the increasing of magnetite volume content of the sample. The spectral information coming from the bandwidth and the attenuations values were used to evaluate the effective frequency of the TDR signal. The attenuation factor values are obtained by. two different methods: i) wave amplitude at the second reflection, ii) electromagnetic parameters (evaluated with L-C-R meters) and TDR band widths. The two methods provide consistent a values within the experimental uncertainties. The agreement supports the possibility of measuring the attenuation factor from the second TDR reflection.

A GPR Investigation in Pompeii (Neaples, Italy) - The Archaeological Area of Nola Gate

The scope of the present work was to test the performance of Ground Penetrating Radar in the volcanic sediments, and to use this technique to investigate the archaeological ruins of one of the most important archaeological and geological sites in the world, Pompeii. The preliminary results demonstrate that the GPR technique is particularly suitable in this type of volcanic terrain. In fact, the survey conducted on the archaeological area of Nola Gate has produced good results both in term of signal penetration and vertical resolution. In particular, the radar data clearly shows a series of reflectors that match well with contacts observed in the geological section, as well as hyperbolic events related to man-made structures.