Mercedes Solla

3D GPR in forensics: Finding a clandestine grave in a mountainous environment

In the present work we show a forensic case study carried out in a mountainous environment. Main objective was to locate a clandestine grave which is around 10-20 years old and contains human remains of one individual and a metallic tool, probably a pick. Survey design started with an experimental burial of a pick at the expected depth (1m) as well as the calculation of synthetic radargrams in order to know if the 250MHz antenna was suitable for its detection and to have a record of the reflection of the pick. Conclusions extracted from the experiments together with rough terrain conditions suggested the use of the 250MHz antenna which allowed a good compromise between target detection and dense grid acquisition of an extensive survey area.

Ancient Stone Bridge Surveying by Ground-Penetrating Radar and Numerical Modeling Methods

Bridges are considered necessary engineering structures because they connect separated lands to improve economic and social development. In Spain, many of the bridges in service within the network of transport are masonry arch bridges built in ancient times. In addition to their age, the stability of these remaining bridges is questionable because of the changing loading conditions; therefore, they require periodic assessment of the condition state. Moreover, some of these bridges are considered a part of the cultural heritage of a region, so nondestructive evaluation is required to preserve their historical character. In this work, a medieval stone bridge in the Galician territory of Spain was evaluated using ground-penetrating radar, supported by a detailed geometric survey performed through a terrestrial laser scanner. The results revealed unknown geometrical data and hidden characteristics, including the thickness of ring stones in the interior of the vault, as well as the presence of ancient arches and restorations. To assist in the interpretation, finite-difference time-domain modeling was used, where realistic models were built from the accurate geometry provided. The synthetic data obtained were compared with the field data, which allowed for the identification of unknown structural details.

GPR Signal Characterization for Automated Landmine and UXO Detection Based on Machine Learning Techniques

Landmine clearance is an ongoing problem that currently affects millions of people around the world. This study evaluates the effectiveness of ground penetrating radar (GPR) in demining and unexploded ordnance detection using 2.3-GHz and 1-GHz high-frequency antennas. An automated detection tool based on machine learning techniques is also presented with the aim of automatically detecting underground explosive artifacts. A GPR survey was conducted on a designed scenario that included the most commonly buried items in historic battle fields, such as mines, projectiles and mortar grenades. The buried targets were identified using both frequencies, although the higher vertical resolution provided by the 2.3-GHz antenna allowed for better recognition of the reflection patterns. The targets were also detected automatically using machine learning techniques. Neural networks and logistic regression algorithms were shown to be able to discriminate between potential targets and clutter. The neural network had the most success, with accuracies ranging from 89% to 92% for the 1-GHz and 2.3-GHz antennas, respectively.

NDT Documentation and Evaluation of the Roman Bridge of Lugo Using GPR and Mobile and Static LiDAR

AbstractThe Roman Bridge of Lugo (Spain) has undergone many restorations throughout the last millennium. It currently supports heavy and constant pressures resulting from traffic loading. Therefore, frequent inspections are required. Within this article, different nondestructive testing (NDT) technologies were combined for the inspection and as-built three-dimensional (3D) documentation of this masonry arch bridge. Both mobile and static light detection and ranging (LiDAR) devices, integrated with digital cameras, were considered to analyze the exterior of the bridge whereas the ground penetrating radar (GPR) equipment was used to characterize its internal stonework. A 3D textured bridge model is given, which is combined with inner details from GPR. Its analysis could certainly benefit masonry arch bridge inspection.

Modelling and strength evaluation of masonry bridges using terrestrial photogrammetry and finite elements

Several numerical models are presented in this article, for the study of the ultimate behaviour of a real stone arch bridge. For the exact representation of the geometry an integral and comprehensive survey involving Terrestrial Photogrammetry and Ground Penetrating Radar is in order to provide a realistic 3D geometric model for the subsequent mechanical analysis of the bridge. The accuracy of the photogrammetric method permitted detecting cracks in different areas and the GPR completed the geometric model with information of hidden parts such as backfill, arch ring thickness, etc. Finite element analysis models, incorporating damage, elastoplasticity and contact, are then developed. Comparison between these models is considered in a single arch of the structure. The classical four hinges mechanism appears in the arch. A model of the whole structure, where the arch and the fill are taken into account, is finally developed. Results show how damage is developed in the body of the arch, for loadings that include forces, or vertical and transverse displacements in the supports.

Experimental forensic scenes for the characterization of ground-penetrating radar wave response

Over the last few decades, the use of non-intrusive geophysical techniques, which allows for coverage of an entire crime scene in a reasonable amount of time, in forensic investigation has increased. In this study, we analyze the effectiveness of ground-penetrating radar (GPR) in forensics. Experimental scenes were simulated and some of the most commonly buried items in actual crime scenes were introduced, such as bone remains, guns and drug caches. Later, a GPR survey was conducted on the experimental grids with a 500 MHz antenna. The final purpose was to characterize the radar wave response expected for each set of remains to assist with its identification in later actual investigations. The results collected provided promising information that can be used when surveying real cases. Nevertheless, there were some interpretational difficulties regarding the sizes of the items and the electromagnetic properties of the materials. For these cases, finite-difference time-domain modeling was employed to achieve an advanced interpretation of the field data. The simulated models used were built from accurate geometric data provided by photogrammetric methods, which replicate the experimental scenes in fine detail. Furthermore, this approach allowed for the simulation of more realistic models, and the synthetic data obtained provided valuable information for assisting in the interpretation of field data. As a result of this work, it was concluded that GPR can be an effective tool when searching for a variety of materials during a crime scene investigation.

Masonry arch bridges evaluation by means of GPR

Some masonry arch bridges in Galicia (NW Spain) were surveyed with GPR using 250 and 500 MHz antennas. The main goal of this work was to perform an analysis of historical bridges, obtaining information about filling material homogeneity, detecting inclusions of different materials, defining structural faults -such as internal voids or cracks- and detecting ancient features -as hidden arches or previous profiles of the bridge-. Geometric 3D models of the surveyed bridges obtained with Laser Scanning methods, were used as inputs to create synthetic radargrams through FDTD simulations in order to help GPR data interpretation.

Assessment of a concrete pre-stressed runway pavement with ground penetrating radar

This paper presents the results of the application of GPR to detect the constitution of a concrete pre-stressed runway pavement and the location of the rebars, with the aim of evaluation the bearing capacity of the runway.

GPR for road inspection: Georeferencing and efficient approach to data processing and visualization

GPR is a recommendable non-destructive technique for thickness measurement of pavement layers because data acquisition takes place at normal traffic speeds, making GPR a cost-effective technique. On the other hand, the large collected data, when the GPR system is mounted on a moving vehicle, is difficult to process. Given that processing is conducted by qualified practitioners, it is a key to obtain software tools that allow for accurate thickness measurements and fast processing times. In this paper, an easy to use and intuitive tool for pavement thickness measurement is presented. Exploiting the power of C++ programming language and the Qt framework advantages for developing applications with graphic interface, a simple and intuitive tool for a qualified worker is implemented in order to reduce the processing times and to give information at the earliest possible moment. Furthermore, the software provides a visualization application for the georeferencing of the field GPR data by using additional GPS (Global Positioning System) data. Given that the GPR acquisition software can connect to an external GPS for trace tagging, NMEA synchronization was used in this case. If the connection is set properly, the GPR acquisition software creates a number of files in order to get the GPR traces paired with a GGA sentence. After post-processing, all the traces are referenced to a SBET (Smooth Best Estimated Trajectory).

Reconstructing the Roman Site “Aquis Querquennis” (Bande, Spain) from GPR, T-LiDAR and IRT Data Fusion

This work presents the three-dimensional (3D) reconstruction of one of the most important archaeological sites in Galicia: “Aquis Querquennis” (Bande, Spain) using in-situ non-invasive ground-penetrating radar (GPR) and Terrestrial Light Detection and Ranging (T-LiDAR) techniques, complemented with infrared thermography. T-LiDAR is used for the recording of the 3D surface of this particular case and provides high resolution 3D digital models. GPR data processing is performed through the novel software tool “toGPRi”, developed by the authors, which allows the creation of a 3D model of the sub-surface and the subsequent XY images or time-slices at different depths. All these products are georeferenced, in such a way that the GPR orthoimages can be combined with the orthoimages from the T-LiDAR for a complete interpretation of the site. In this way, the GPR technique allows for the detection of the structures of the barracks that are buried, and their distribution is completed with the structure measured by the T-LiDAR on the surface. In addition, the detection of buried elements made possible the identification and labelling of the structures of the surface and their uses. These structures are additionally inspected with infrared thermography (IRT) to determine their conservation condition and distinguish between original and subsequent constructions.