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Featured Application: Imaging in stratified media and imaging of buried cavities. This contribution deals with the focusing and time–depth conversion of GPR data in a two-layer scenario. In a layered scenario, the different propagation velocities of the electromagnetic waves in different layers can induce distortion in the reconstruction. In particular, it is not possible, with common data processing, to achieve the focusing of both the targets embedded in the upper and deeper layers at the same time. We will present a strategy for mitigating this problem. The strength points of this strategy are its simplicity and the fact that it only requires a commercial code for the GPR data processing plus some steps easily implementable through a homemade code. This work extends a contribution of the same authors at the 20th International GPR conference held in Chanchung, China, in June 2024, and the conclusions are updated with three-dimensional numerical results, including depth slices determined directly in the spatial domain. Both numerical and experimental data will be shown. [ABSTRACT FROM AUTHOR]

The paper deals with a combined time–depth conversion strategy able to improve the reconstruction of voids embedded in an opaque medium, such as cavities, caves, empty hypogeal rooms, and similar targets. The combined time–depth conversion accounts for the propagation velocity of the electromagnetic waves both in free space and in the embedding medium, and it allows better imaging and interpretation of the underground scenario. To assess the strategy's effectiveness, ground penetrating radar (GPR) data referred to as an experimental test in controlled conditions are accounted for and processed by two different approaches to achieve focused images of the scenario under test. The first approach is based on a classical migration algorithm, while the second one faces the imaging as a linear inverse scattering approach. The results corroborate that the combined time–depth conversion improves the imaging in both cases. [ABSTRACT FROM AUTHOR]

This paper deals with ground‐penetrating radar prospecting and exploits a semi‐heuristic strategy to account for inhomogeneous background media, empty cavities or topography of the surface. We assume here that no more than a commercial processing software is available. Customarily, commercial codes assume a homogeneous soil and a flat interface in order to achieve the focusing of the data. Therefore, this is also the model exploited here, whereas the data are referred to an inhomogeneous soil or to a non‐flat interface. The proposed strategy exploits the principle that 'the data speak', even if with some ambiguity and some reticence, and they can reveal or at least suggest important features of the underground scenario. On this basis, heuristically, we exploit features derived from the data themselves as a posteriori information, improving the available focusing and time–depth conversion even having at disposal a basic model of the background scenario. [ABSTRACT FROM AUTHOR]

In this work, we present a case history relative to ground penetrating radar measurements performed close to the Roman amphitheatre of Lecce, Italy. We have performed a classical data elaboration with focusing of the data and slicing putting into evidence hidden details of the structure of the monument. It will be shown that the interpretation of the ground penetrating radar data is meaningfully helped by the consultation of ancient documents, which makes the final result multidisciplinary. Finally, we have georeferenced the data matching the shape of the depth slices with the shape of the investigated roads. In fact, we did not have at disposal any differential global satellite navigation systems. Indeed, this can be a method exploitable in cases when satellite data are not available, either because the area is shadowed or because the user does not have a differential global satellite navigation system. The proposed geographical matching is achieved by means of the matching between the shape of the slices and those of the physical obstacles present in the field. Therefore, it is essentially based on a continuous of points, and so it is probably more precise than a method based on the only vertexes. In particular, the proposed procedure does not require any deformation of the shape of the slice. [ABSTRACT FROM AUTHOR]

This document is an introduction to a special issue of the journal Geophysical Prospecting on "Advanced techniques, methods, and applications for an integrated approach to geophysical prospecting." The issue focuses on the use of integrated approaches in geophysics, which involve the intelligent use of multiple techniques and the combination of their results. The special issue includes 14 papers that cover a range of techniques such as seismic, geoelectric, ground-penetrating radar (GPR), and magneto-telluric, as well as various applications including mining, cultural heritage, and geological evaluations. The papers explore topics such as reservoir modeling, water reservoir mapping, machine learning algorithms, mine structure detection, and archaeological investigations. The document concludes with acknowledgments and a statement that the data are available upon request. [Extracted from the article]

In this article we present the results of a geomorphological and geophysical investigation carried out in the Regional Park of Matera Murgia, also known as Park of the Rupestrian Churches (world site protected by UNESCO), in Basilicata region, southern Italy. The aim of this investigation is to support the scheduled restoration works in some rupestrian historical sites and the safety of the tourist route that connects the churches along the eastern side of Gravina river valley. In particular, a ground penetrating radar (GPR) prospection was conducted on frescoed surfaces in two rupestrian churches permitting the detection of different kinds of problems affecting the fresco surfaces, such as lesions and efflorescence. [ABSTRACT FROM AUTHOR]

Ground-penetrating radar (GPR) mapping provides a three-dimensional analysis of archaeological features within the context of landscape studies. The method's ability to measure the intensity of radar reflections from deep in the ground can produce images and maps of buried features not visible on the surface. A study was conducted in some areas near the Domus Romana in Rabat (Malta) in order to investigate the still uncovered archaeological structures. The purpose of the GPR survey was to guide the excavation operations (planned but postponed due to Covid-19) and to allow us to understand the development of the defensive walls of the city and any other structures related to the Roman mansion. The choice of the areas to be investigated was therefore guided both by previous archaeological excavations and by the considerations made above. The results obtained through the GPR made it possible to shed light on some of the aspects related to the questions posed by the archaeologists, highlighting part of the structures related to the defensive walls, part of the structures related to water supply and conservation and part of the wall structures related to the Roman mansion itself. [ABSTRACT FROM AUTHOR]

In this contribution we will show the results of a non-invasive GPR prospecting performed in the archaeological site of San Vito dei Normanni, in the outskirts of Brindisi, Apulia region, southern Italy, where the ancient population of the Messapians had an important settlement. The present work was performed in the framework of a school in the field financed by the Basilicata Region. The interpretation of the data has been based on the depth slices, on the processed Bscans and on the apriori available information is provided. Future excavations will be driven also by the results achieved from this GPR prospecting. [ABSTRACT FROM AUTHOR]

This paper is inserted into the framework of inverse scattering with application to Ground Penetrating Radar (GPR) data and is meant to provide a method helping to apply inverse scattering algorithms to electrically large investigation domains. In particular, we focus on the depth slices that are particularly important in application on cultural heritage and propose in relationship with the depth slices a strategy that we will call “shifting zoom” that is specifically a method to mitigate the effects of the limited view angle in the linear tomographic inversion applied to GPR data. In particular, this paper is an extended version of the contribution (Persico et al. in: Proceedings of Imeko international conference on metrology for archaeology and cultural heritage, Lecce, Italy, 2017a), published in the Proceedings of the conference metrology for archaeology 2017. We propose here a validation of the shifting zoom versus experimental data gathered in a controlled test site, and we will show the effect of the shifting zoom on depth slices achieved from these data after a linear inverse scattering processing has been applied for their focusing. [ABSTRACT FROM AUTHOR]

Linear inverse scattering problems can be solved by regularized inversion of a matrix, whose calculation and inversion may require significant computing resources, in particular, a significant amount of RAM memory. This effort is dependent on the extent of the investigation domain, which drives a large amount of data to be gathered and a large number of unknowns to be looked for, when this domain becomes electrically large. This leads, in turn, to the problem of inversion of excessively large matrices. Here, we consider the problem of a ground-penetrating radar (GPR) survey in two-dimensional (2D) geometry, with antennas at an electrically short distance from the soil. In particular, we present a strategy to afford inversion of large investigation domains, based on a shifting zoom procedure. The proposed strategy was successfully validated using experimental radar data. [ABSTRACT FROM AUTHOR]

In this contribution, some possible effects of large band electromagnetic interferences on Ground Penetrating Radar (GPR) data are shown, and a possible way to counteract them is shown, too. The mitigation of the interferences is implemented thanks to a prototypal reconfigurable stepped frequency GPR system, that allows to program the integration time of the harmonic tones vs. the frequency. In particular, an algorithm for the measurement of the effects of the interferences in the field (linked to the signal to interference ratio) is proposed and tested vs. experimental data. The paper will show some advantages and some drawbacks of the proposed procedure. [ABSTRACT FROM AUTHOR]

This paper presents ground penetrating radar (GPR) results joined with and back-upped by endoscopic tests performed in two churches. The aim of this work is to show how the endoscopic tests can help the interpretation of the achieved GPR images, and this will be shown with respect to two case histories in southern Italy. The usefulness of the endoscopic tests depends on the kind of targets, but is expected to be particularly useful in cases of buried cavities, where information about the volume and the possible past use of the cavity can be retrieved. In the examined cases, the endoscopic tests allowed the presence of three cavities to be established, helping also in the interpretation of their possible nature and use, even if the endoscopic probe was not gyroscopic nor equipped with a laser for the precise measure of the distances. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

In this paper, we propose an automated detection algorithm for well- and ill-shaped ground-penetrating radar reflection hyperbolas for complex media, calibrated with human recognition principles. The algorithm detects the apex of the hyperbolas by fitting an analytical function of a hyperbola to the profile edge dots detected with a Canny filter. The existence of a hyperbola is determined using a set of carefully chosen criteria calibrated in order to fit the ambiguity zone for the human brain. The inherent misshapedness of field hyperbolas is further considered by defining a buffer zone around the theoretical hyperbola. First, the method was tested in the laboratory over tree roots and PVC pipes and on field images over tree root systems. Both time- and frequency-domain radars were used on-ground. After around 1–3 min of computation time for 10 000 edge dots in a MATLAB environment (single 1.96-GHz processor), the results showed rates of false alarm and nondetection of maximum 20% and 28%, respectively. In comparison with the semiautomated hyperbola detection provided by a commercial software, these rates were lower. Second, we conducted a sensitivity analysis to estimate the validity of the fitting of a hyperbola equation neglecting the object radius. The fitting was close, but the derivation of the relative permittivity from the analytical equation neglecting the radius led to high errors. In conclusion, owing to the low computational time and its good performances, the proposed algorithm is suitable for complex environments. [ABSTRACT FROM AUTHOR]

In this paper, we show the results of three case histories where GPR prospecting has been interpreted also with the aid of a specific archive research on documents of the XVI and XVII century. The case histories are related to three churches of the renaissance and baroque period in Lecce, Lecce, Southern Italy. The aim is to deliver the usefulness of GPR prospecting in these kind of monuments and to show how the likelihood of the interpretation can be increased when historical information is available. [ABSTRACT FROM AUTHOR]

We focus on the choice of the investigation domains for a 2-D linear inversion algorithm based on the Born approximation. The application of an inversion algorithm to a wide B-scan requires the subdivision of the data into several observation domains and the partition of the buried scenario into different investigation domains, and this can be done in many ways, which raises the problem of examining the well advisedness of the adopted choice. In particular, here, we will propose the possibility of a double sequence of investigation domains. The results will also be compared with a migration algorithm. [ABSTRACT FROM PUBLISHER]

This paper deals with the reconstruction of buried targets exhibiting both dielectric and magnetic characteristics, starting from GPR data collected at the interface air/soil. The problem is tackled under the Born approximation. In particular, two-dimensional migration and linear inversion results will be compared versus experimental data and three-dimensional representations of the reconstructions achieved from both methods will be shown. [ABSTRACT FROM AUTHOR]

The Romano-British site of Barcombe in East Sussex, England, has suffered heavy postdepositional attrition through reuse of the building materials for the effects of ploughing. A detailed GPR survey of the site was carried out in 2001, with results, achieved by usual radar data processing, published in 2002. The current paper reexamines the GPR data using microwave tomography approach, based on a linear inverse scattering model, and a 3D visualization that permits to improve the definition of the villa plan and reexamine the possibility of detecting earlier prehistoric remains. [ABSTRACT FROM AUTHOR]

In this contribution, we propose ground-penetrating radar (GPR) investigation performed close and on some prehistoric tumuli, locally called "piccole specchie", in the countryside around the town of Parabita (Lecce), within the Salento peninsula (southern Italy). In order to perform the GPR investigation on the tumuli, an unconventional method of data acquisition was exploited, involving, consequently, some non-conventional data processing steps. Photogrammetric survey was also performed, and 3D digital models of the prehistoric tumuli were created. The investigations have revealed some anomalies under two out of three investigated tumuli, which were interpreted as prehistoric tombs. [ABSTRACT FROM AUTHOR]

We study the impedance parameters and the energy transmitted and received by a couple of antennas working in a nonhomogeneous background. The focus is on stepped frequency ground penetrating radar (SF-GPR) prospecting. In particular, we propose a reconfiguration of the GPR system versus the frequency that accounts for the background scenario, and we show that the reconfiguration can improve the frequency behavior of the antennas significantly. Tests performed on two bow-tie antennas will be shown. [ABSTRACT FROM PUBLISHER]

This paper deals with the application of a frequency-domain microwave-tomography-imaging algorithm to a multibistatic configuration in ground-penetrating-radar applications. First, the authors formulate the inverse problem as a linear one by exploiting the Born approximation. Then, the reconstruction capabilities of the solution algorithm are investigated, and an optimal frequency step to be adopted for the reconstruction is discussed and determined. Finally, inversion results are presented with synthetic data obtained from time-domain simulations and then Fourier transformed in frequency domain. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we present some possibilities offered by an inverse scattering approach in the reconstruction of hidden objects using ground penetrating radar (GPR) on time-domain experimental data. We will show that an inverse scattering approach can allow the detection and the determination of the geometrical features of the targets in an automatic way, thus reducing the dependence of the “interpretation” from the personal expertise of the human operator. In particular, this can be made by exploiting a linear approximation of the electromagnetic scattering that allows us to achieve effective and reliable inversion algorithm. [Copyright &y& Elsevier]

This paper deals with a linear two-dimensional inverse scattering problem within a half space geometry with data gathered far away from the interface, which is relevant in ground penetrating radar contactless data processing. In particular, the role of the measurement configuration is discussed with regard to the information retrievable from multifrequency data. [ABSTRACT FROM AUTHOR]

In this contribution, we present some results achieved in the archaeological site of Le Cesine, close to Lecce, in southern Italy. The investigations have been performed in a site close to the Adriatic Sea, only slightly explored up to now, and where the presence of an ancient Roman harbour is alleged on the basis of remains visible above all under the current sea level. This measurement campaign has been performed in the framework of a short-term scientific mission (STSM) performed in the framework of the European Cost Action 17131 (acronym SAGA), and has been aimed to identify possible points where future localized excavation might and hopefully will be performed in the next few years. Both a traditional elaboration and an innovative data processing based on a linear inverse scattering model have been performed on the data. [ABSTRACT FROM AUTHOR]

As the frequency of earthquakes has increased in Korea in recent years, designing earthquake-resistant facilities has been increasingly emphasized. Structures constructed with rebars are vulnerable to shaking, which reduces their seismic performance and may result in damage to human life and property. Because the construction of facilities requires the maintenance of sub-constructions, such as by cutting rebars or compensating for missing rebars, information on rebar diameter is required. In this study, the YOLO-v3 algorithm, which has the fastest object recognition performance, was applied to the structural correction data, and a basic experiment was conducted in the air to predict the diameter of rebars in a facility, in real time based on ground-penetrating radar data. The reason for using the YOLO-v3 algorithm is that in the case of GPR data that change slightly according to the diameter of the reinforcing bar, it is difficult to discriminate with the naked eye, and the result may change depending on the inspector. The model achieved a higher accuracy than conventional rebar detection and diameter prediction methods. In addition, the possibility of real-time rebar diameter prediction during construction, using the proposed method, was verified. [ABSTRACT FROM AUTHOR]

In this paper, we propose the combination of different migration results achieved on the same data in order to account for different values of the propagation velocities of the electromagnetic waves within the considered Ground Penetrating Radar (GPR) profile. These different values can be the result of a variable lithological composition or (more probably for short Bscans) the results of different moisture levels, or both. Here, we separately consider the two cases of horizontal or vertical variability of the propagation velocity with a transition zone between two zones with constant propagation velocity. Moreover, we also propose a time-depth conversion accounting for these different values of the propagation velocity along the considered GPR Bscan. The method is applied to real data gathered in the field with regard to a concrete coverage containing liner layers. [ABSTRACT FROM AUTHOR]

The regular application of geophysical survey techniques to evaluate archaeological sites is well established as a method for locating, defining, and mapping buried archaeological materials. However, it is not always feasible to apply a range of different methods over a particular site or landscape due to constraints in time or funding. This paper addresses the integrated application of three geophysical survey methods over an important archaeological site located in south Italy. In particular, it is focused on the results achieved from a past geophysical survey and the ongoing excavations performed by archaeologists in the site of Muro Leccese. Muro Leccese (Lecce) is one of the most important Messapian archaeological sites in southern Italy. The archaeological interest of the site was generated since the discovery of the remains of Messapian walls (late 4th–3rd centuries BC). With the aim of widening the archaeological knowledge of the Messapian settlement, several integrated methods, including magnetometry, ground-penetrating radar, and electrical resistivity tomography were used on site to fulfill a number of different research objectives. Since the most important targets were expected to be located at shallow soil depth, a three-dimensional (3D) ground-penetrating radar (GPR) survey was carried out in two zones, which were labeled respectively as zone 1 and zone 2, and were both quite close to the archaeological excavations. The GPR investigations were integrated with a 3D electrical resistivity tomography (ERT) survey in zone 1 and with a magnetometric, in gradiometry configuration survey in zone 2. The integration of several techniques allowed mapping the structural remains of this area and leading the excavation project. The geophysical results show a good correspondence with the archaeological features that were found after the excavation. Current work on the geophysical survey data using different codes for the processing of the data and merging different datasets using a Geographic Information System allowed achieving a user-friendly visualization that was presented to the archaeologists. [ABSTRACT FROM AUTHOR]

The bilateral project "Non-invasive investigations to enhance the knowledge and the enjoyment of cultural heritage", conducted together by the Institute for Archaeological and Monumental Heritage IBAM-CNR and the Department of Geoscience of the University of Malta, has allowed to schedule performed integrated geophysical prospections [1] both in Italy and in Malta, part of which have been already performed. In this contribution, we will describe a work regarding the Roman amphitheatre of Lecce, Italy, where ground penetrating radar and passive seismic measurements were performed. The amphitheatre of Lecce is a particular monument because it is only partially visible. In particular, its memory was lost and its traces appeared causally when digging for a building work at the beginning of last century. It was not possible to excavate it entirely because of the presence of subsequent structures, by now historical in their turn, of renaissance-baroque style. In particular, the "ambulacra", i.e. the corridors under the steps that originally surrounded the entire arena, are walled at a certain point and it is not known if they continue or not beyond the current limit up to form a closed ring, or if they collapsed. In particular, part of these ambulacra prolong under the current St Oronzo square, and we have performed geophysical investigation in the square and in particular in an area where the buried ambulacra, if still present should pass. The investigations reveals that it is probable that, at least partially, the ambulacra continue, but it is not possible to establish if they join from both sides and still form an elliptical ring under the square, also because the vertex of the ellipsis should be placed under a church where we could not perform prospections at the moment. AcknowledgmentsThis work has been performed thanks to the support of the bilateral project "Noninvasive investigations for enhancing the knowledge and the valorization of the cultural heritage", carried out by the Institute for Archaeological and Monumental Heritage IBAM-CNR and the Department of Geoscience of the University of Malta.ReferencesInnovative Instrumentation and Data Processing Methods in Near Surface Geophysics, edited by R. Persico, S. Piro and N. Linford, Elsevier, ISBN 978-0-12-812429-1, 2018. [ABSTRACT FROM AUTHOR]

Abstract: In this paper we deal with an indirect measure of the dielectric permittivity of the soil starting from GPR surface data collected on a buried “cooperative” target, meant as an object buried on purpose and whose extent is known a-priori. This target is exploited in order to achieve, from its image obtained from a suitable GPR data processing, an indirect measure of the dielectric permittivity of the embedding soil. GPR data processing is based on a linear microwave tomographic approach funded on the Born Approximation. Using this Born approach on two-dimensional inversion tests, we investigate the effect of the soil''s electrical conductivity and permittivity on this indirect measure and demonstrate that the electrical field scattered by a spot-like buried object permits an accurate estimation of the soil permittivity even when no information of the soil conductivity is available. [Copyright &y& Elsevier]

In this paper, the results of a ground penetrating radar (GPR) prospecting survey performed in the Roman archaeological site of Aquinum are shown. The prospecting was performed in two distinct areas. The first one was close to the remains of the ancient thermal baths, where a public project intends to build a car park. The second area is close to an apsidal Roman building, and it was of interest to establish whether, and possibly up to what extent, the remains of this partially revealed structure continue, or maybe whether meaningful further structures are present. [ABSTRACT FROM AUTHOR]

This paper is focused on the presentation and discussion of an object oriented approach, applied to the Hierapolis (Turkey) site, to automatically detect the subtle features linked to buried archaeological remains. The data processing is applied twice: (i) first, globally at the whole image and, (ii) second, at the significant subsets identified by global analysis, in order to refine the previously obtained categorization. Object oriented approaches are usually based on two main steps: i) first the segmentation, ii) then the classification. Herein, we first performed the unsupervised classification step and, then, the segmentation. This choice is given by the specificity of archaeological issue, in particular: (i) the subtle features/targets to be identified are partially or totally unknown and characterized by a very small spectral separability from the background, and therefore (ii) the discrimination between archaeological class and substrates likely suffers significant confusion. To cope with these issues, the first step is based on an unsupervised classification, which provides a first ‘rough’ categorization of pixels; the second step, based on the segmentation, enables us to extract the geometric shape, and, in turn, to only categorize as archaeological class those pixels belonging to geometrically (rectangular and linear) shaped clusters. Outputs from this classification identify rectangular and linear features of archaeological interest whose size suggested that they may be a farm and some sectors of an aqueduct, respectively. Results from satellite based analysis were successfully evaluated by georadar and geomagnetic prospection along with field survey. From georadar and geomagnetic prospection we were able i) to confirm the presence of buried remains and ii) to detail and characterize these archaeological features at the subsoil level as well as to define the local stratigraphy. From field survey we dated the detected buried remains to a period spanning from Imperial Roman to early Byzantine historical times. [ABSTRACT FROM AUTHOR]