Journal Papers Working Group 4   (with acknowledgement to COST Action TU1208)

Archaeology & Cultural heritage (from the most recent paper to the oldest)

[wg4-ACH-j3] S. Santos-Assunçao, K. Dimitriadis, Y. Konstantakis, V. Perez-Gracia, E. Anagnostopoulou, R. Gonzalez-Drigo, "Ground-penetrating radar evaluation of the ancient Mycenaean monument Tholos Acharnon tomb," EAGE Near Surface Geophysics (NSG), vol. 14(2), pp. 197-205, April 2016, doi: 10.3997/1873-0604.2015030 (Spain, Greece; STSM Outcome; INDUSTRY INVOLVEMENT; TU1208 NSG Special Issue) 

Abstract: The assessment of cultural heritage requires high-resolution and non-destructive methodologies. Ground-penetrating radar is widely applied in the inspection of historical buildings. However, some structures with curved surfaces make the radar data acquisition process difficult and consequently the following data interpretation. This paper describes a case study concerning a circular and buried Greek monument. This monument is a magnificent tomb buried with irregular stones. However, its structure and the internal stones arrangement are unknown. Therefore, a radar survey was carried out to achieve two main objectives: (i) identification of hidden elements and arrangement of the stones and (ii) detection of specific zones where further restoration and maintenance should be recommended. The methodology for the radar data acquisition involves the use of a laser scan in order to define accurately each radar line, covering all the internal surface of the tomb. Radar data processing was developed by converting Cartesian coordinates into polar coordinates. This proce- dure allows defining better the internal anomalies, improving the radar data interpretation. The main results of the survey were three: (i) the presence of a hidden target buried in the corridor access to the tomb; (ii) the description of the internal structure of the walls of the tomb, defining the stones arrangement and the position and depth to the keystone; and (iii) the existence of delimited zones where the signal is highly attenuated, probably due to a high salt content.

[wg4-ACH-j2] M. Solla, R. Asorey-Cacheda, X. Núñez-Nieto, B. Conde-Carnero, “Evaluation of historical bridges through recreation of GPR models with the FDTD algorithm,”  Construction and Building Materials (Elsevier), vol. 77, pp. 19-27, January 2016; doi: 10.1016/j.ndteint.2015.09.003 (Spain)

Abstract: This work presents the evaluation of a medieval masonry bridge that has suffered different restorations throughout history. Ground penetrating radar was used to define the internal state of the structure. Given that the heterogeneity in masonry complicates the interpretation of field data, numerical modelling was employed to improve such interpretation. The combination of photogrammetric and thermographic data, jointly with the development of custom algorithms, was used to create the synthetic model; while real GPR data supported the media characterization. The resulting data allowed for the interpretation of both composition and distribution of different materials in the interior of the bridge.

[wg4-ACH-j1] V. Pérez-Gracia, J. O. Caselles, J. Clapés, G. Martinez, and R. Osorio, “Non-destructive analysis in cultural heritage buildings: Evaluating the Mallorca cathedral supporting structures,” Non Destructive Testing and Evaluation International (Elsevier), vol. 59, pp. 40–47, October 2013; doi: 10.1016/j.ndteint.2013.04.014 (Spain)

Abstract: Geophysical prospecting surveys are being increasingly used in non-destructive evaluations of structures, and several methods can be applied in the evaluation of cultural heritage buildings. However, accurate studies of cultural heritage structures usually need the application of combined techniques, historic and structural knowledge also being necessary. The present paper describes the application of two non- destructive testing techniques: ground-penetrating radar and seismic tomography, in the analysis of some structural elements' inner geometries and physical properties. This job is part of a more complete project developed to define the Mallorca Cathedral structural behaviour. Both geophysical methods are used in a complementary way. GPR allows the detection of small anomalies (changes of about centimetres), and the results are used to select the most appropriate seismic tomography initial model. The aim of the study is to define the internal structural configuration as well as the stone quality. Results reveal the internal structure of columns, walls and buttresses, showing different structural elements. Even when the visual inspection points to external damages, the detailed NDT evaluation indicates that the inner structure is in good condition and the ashlars are of good quality.

Geology, Geophysics & Geotechnics  (from the most recent paper to the oldest)

[wg4-GGG-j3] A. Gosar, T. Čeru, “Search for an artificially buried karst cave entrance using ground penetrating radar: a successful case of locating the S-19 Cave in the Mt. Kanin massif (NW Slovenia),” International Journal of Speleology, vol. 45(2), pp. 135-147, May 2016; doi: 10.5038/1827-806X.45.2.1979 (Slovenia; OPEN ACCESS)

Abstract: The S-19 Cave was with its explored depth of 177 m one of the most important caves of the Mt. Kanin massif, but after its discovery in 1974, a huge snow avalanche protection dyke was constructed across the cave entrance. To excavate the buried cave, the accurate location of the cave had to be determined first. Since the entrance coordinates were incorrect and no markers were available, application of geophysical techniques was necessary to do this. A Ground Penetrating Radar (GPR) with special 50 MHz rough terrain antennas was selected as the single suitable geophysical method for the given conditions where thick debris overlay a rugged limestone surface. Nevertheless, it was not possible to directly detect the relatively narrow cave entrance itself due to data resolution limits. However, a historical photo of the area showed that the cave entrance was located in a local depression, which therefore represented the main target of the GPR survey. Seven GPR profiles were measured across the rough and steep surface causing difficulties in traversing the area with sensitive research equipment. In all recorded radargrams a small depression was clearly imaged under debris, and recognized as a topographic feature with the cave entrance. Based on the GPR data interpretation, the exact location for digging was determined and the thickness of debris assessed at 6.5–7 m. A massive excavation by a dredger resulted in a successful opening of the cave entrance, confirming both its geophysically determined location and its estimated depth. The application of an advanced geophysical method was therefore proven successful in providing a solution to this specific case in karst exploration and an important cave was saved.

[wg4-GGG-j2] S. Santos-Assunçao, V. Perez-Gracia, V. Salinas, O. Caselles, R. Gonzalez-Drigo, L. G. Pujades, N. Lantada, "GPR Backscattering Intensity Analysis Applied to Detect Paleochannels and Infilled Streams for Seismic Nanozonation in Urban Environments,"  IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing (JSTARS), vol. 9(1), pp. 167-177, January 2016; doi: 10.1109/JSTARS.2015.2466235  (Spain; GPR 2014 Special Issue)

Abstract: Seismic microzonation of urban areas is used to be determined from few soils’ response measurements in each area. In consequence, results can be considered correct only in the case of possible depth-dependent soils, being the existence of lateral soil changes the cause of imprecision. Ground-penetrating radar (GPR) could be a useful tool to determine, previously to the pas- sive seismic measurements, the location of geological structures. Moreover, depending on the ground materials, the GPR energy is randomly backscattered. Consequently, the background noise in the radar scans increases. Therefore, the analysis of the amplitude of the noise could be a useful method to determine changes on the ground characteristics. The analysis of the background GPR amplitude noise is tested in two radar lines, crossing the city of Barcelona. The results show significant differences in the back- ground noise amplitude in the A-scans that could be used to define zones in the city depending on the noise level. These changes on the amplitude are associated with the backscattered energy as a conse- quence of soil characteristics. Hence, the analysis of the variation in the background noise amplitude allows defining the possible location of subterranean streams, paleochannels, and other struc- tures crossing the plain of the city. Radar results are also compared to ambient vibration measurements, using the spectral horizontal- to-vertical (H/V) quotient, and to historical and contemporary information. The application of the methodology underscores the ability of the evaluation of the backscattering associated with the background noise in the scans in the detection of sharp geological changes in sedimentary deposits.

[wg4-GGG-j1] M. Zajc, B. Celarc, A. Gosar, "Structural–geological and karst feature investigations of the limestone–flysch thrust-fault contact using low-frequency ground penetrating radar (Adria–Dinarides thrust zone, SW Slovenia),"  Environmental Earth Sciences (Springer), vol. 73(12), pp. 8237-8249,  June 2015; doi:  10.1007/s12665-014-3987-x (Slovenia) 

Abstract:  The Karstic thrust edge, a pronounced geomorphologic step, which is a result of the tectonostratigraphic evolution of the active Adria–Dinarides thrust zone, represents a major obstacle for the planned new railway route Divača–Koper. Thus, the geotechnical and structural properties as well as the geometry of the thrust-fault planes in this area are of great importance. Since geological mapping cannot give insight into the subsurface to reveal a complex 3D structure, and the numerous boreholes needed to investigate the area would be too expensive and time consuming, the application of a geophysical method such as ground penetrating radar (GPR) is needed. To test the method for determining near surface features and detecting low-angle inclined thrusts, a low frequency GPR system with 50 MHz rough terrain antenna was used to record 13 GPR profiles along all three floors of the Črnotiče quarry, where the spatial position of the Socerb thrust fault that separates limestones above and flysch layers below is relatively well documented. The profiles were positioned across selected existing boreholes. The GPR results were correlated with borehole data as well as geological mapping results. The GPR provided not only precise information on the geometry of the Socerb thrust fault, but was also very useful for establishing the position of some known as well as several potential cavities, both air- and sediment-filled. In areas further from the thrust-fault zone, where the limestone is less tectonically damaged, it was also possible to determine apparent dip angles of the strata, which after reconstruction matched the true dips gathered from geological mapping.

Humanitarian applications of GPR: Vital signs of buried and trapped people - UXO  (from the most recent  to the oldest)

[wg4-H-j3] S. Kadioğlu, Y.K. Kadioğlu, “Visualization of buried anti-tank landmines and soil pollution: analyses using ground penetrating radar method with attributes and petrographical methods,” EAGE Near Surface Geophysics (NSG), vol. 14(2), pp. 183-195, April 2016, doi: 10.3997/ 1873-0604.2016010 (Turkey; TU1208 NSG Special Issue)

Abstract: This paper presents an approximation to display buried anti-tank landmines with ground-penetrating radar method, including physical data attributes by measuring data in a special military field and determination of soil pollution using mineralogical and chemical features of the soil obtained by confocal Raman spectrometry and polarized energy dispersive X-ray fluorescence, which are petrographical methods, before and after bursting the mine. Two-dimensional ground penetrating radar data were acquired on parallel profiles using 800-MHz shielded antenna on unexploded anti-tank landmines buried approximately 10 cm–15 cm in depth. After general processing in the time domain, we employed migration, a frequency–wavenumber (F–K) filter, and ground-penetrating radar data attributes with an amplitude envelope, spectral whitening, and first-time derivative to activate anti-tank landmine visualization. Finally, we obtained three-dimensional half bird’s eye view of the processed volume with each separate attribute. We also derived the transparent threedimensional volumes by assigning opacity to the amplitude–colour range. The results showed that the depth slices including attributes and the transparent three-dimensional depth–volumes could clearly image the anti-tank landmine. In addition, migration and F–K filter during special processing were very important in removing data noise. Ground-penetrating radar data attributes—particularly amplitude enveloping— could suppress small phase shifts in the neighbouring traces of the landmine amplitude anomalies and helped to obtain more complete results showing location and depth in the three-dimensional volume. The results of the analyses of the major oxide elements and heavy metal elements, such as Fe2O3, Pb, Zn, As, Mn, Mo, Co, Ni, Sb, and Sn, in the test area revealed that there were almost no major differences before and after blasting the anti-tank landmines. This indicates that one-time bursting of the anti-tank landmines in the field has not polluted the soil in this area.

[wg4-H-j2] V. Ferrara, “Technical Survey About Available Technologies For Detecting Buried People Under Rubble Or Avalanches,” WIT Transaction on The Built Environment, vol. 150, pp. 91-101, May 2015; doi: 10.2495/DMAN150091 (Italy; OPEN ACCESS)

Abstract: Among all activities carried out in disaster scenarios, such as collapsed buildings, earthquakes, and avalanches, the detection and rescue of buried or trapped people have the priority. The paper aims at presenting the progress in the technological development of electronic devices and systems used to detect people buried under rubbles or avalanches. Many technologies realize detection, but only electromagnetic ones assure best results in terms of speed and accuracy of a relief, working also in a noisy environment. We can divide the methodologies using electromagnetic propagation in the three main. One is based on detection of active or passive electronic devices carried by the victim; the second one detects the body of a person as perturbation of the backscattered electromagnetic wave, due to dielectric discontinuity in the medium; the third case is based on the detection of vital signs. Both last two methodologies can be suitable for detecting people trapped under rubbles that can be free to move, also partially. More frequently, a buried person is motionless, because he is unconscious or the ruins block him. Consequently, the detection of vital signs, such as heartbeat or breathing, is the unique possible only. Performances and limits of each method is presented in the article, together with possible innovations.

[wg4-H-j1] X. Núñez-Nieto, M. Solla, P. Gómez-Pérez, and H. Lorenzo “GPR Signal Characterization for Automated Landmine and UXO Detection Based on Machine Learning Techniques,” Remote Sensing, vol. 6(10), pp. 9729-9748, October 2014; doi:10.3390/rs6109729  (Spain; OPEN ACCESS)

Abstract: 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.

Environment

[wg4-E-j1] J. Jezova, L. Mertens, S. Lambot, “Ground-penetrating radar for observing tree trunks and other cylindrical objects,” Construction and Building Materials, vol. 123, pp. 214-225, October 2016, doi: 10.1016/j.conbuildmat.2016.07.005 (Belgium)

Abstract: To improve forest management and to prevent collapses of trees, it is necessary to investigate the internal part of tree trunks. In order to do it non-invasively, ground-penetrating radar (GPR) appears as a promising inspection device. The objective of this paper is to investigate particularities of tree trunks radar images, considering the circumferential data acquisition geometry, as a function of the radar configuration and trunk section structures. In order to better understand this kind of data, a target reflection curve was analytically described, then, the total internal reflection (TIR) phenomenon was explained and illustrated. Subsequently, classical radar measurements were compared with an application of differently shaped (planar and circular) metal shields acting as perfect electrical conductors (PEC). For comparing the methods, three experiments were performed: (1) numerical simulations using the software gprMax2D, based on Finite-Difference Time-Domain method, (2) GPR investigation of a laboratory model of a tree trunk, (3) real tree trunk measurements. The use of a planar or circular PEC increased the visibility of the medium edges, so, these GPR images were considered of a better quality. Internal object reflection curve and TIR detection were essential for general description of a GPR image. All experiments showed satisfactorily the internal inhomogeneity and the information will be useful for future tomographic reconstruction.

Combined use of GPR & complementary NDT techniques  in civil engineering (from the most recent paper to the oldest)

[wg4-NDT-j5] V. Marecos, M. Solla, S. Fontul, and V. Antunes, “Assessing the pavement subgrade by combining different non-destructive methods,” Construction and Building Materials, vol. 135, pp. 76-85, March 2017, doi: 10.1016/j.conbuildmat.2017.01.003 (Spain, Portugal; STSM Outcome)

Abstract: The subgrade provides support to the pavement system and assures an effective distribution of traffic loads in depth. Therefore, a failure in the subgrade will have consequences on the entire pavement behaviour. This work presents an integrated approach for the analysis of the road subgrade condition by combining different Non-Destructive Testing (NDT) techniques. Different Ground Penetrating Radar (GPR) systems, both antennas configuration and frequencies, were tested in order to achieve the best methodology for subgrade cracking detection. Additionally, NDT load tests were performed with two deflectometers, Falling Weight Deflectometer (FWD) and Light Weight Deflectometer (LWD), aiming to determine the elastic modulus of the subgrade and consequently detect damaged areas. The tests were conducted at a real scale test section built to simulate pavement foundation layers consisting of clay soil subgrade, frequently used in African countries. The main tests performed are presented and analysed in this paper. Troubleshooting’s are referred mainly related with GPR wave propagation on clayey materials, due to high absorption. Recommendations are made regarding the use of GPR antennas as air-coupled antennas lead to a better identification of pavement layer interfaces while ground-coupled antennas were preferable to detect anomalous areas, namely cracking and debonding. The results showed good agreement between both NDT methods (GPR and load tests) in the identification of the anomalous areas and were validated with some in-situ cores extracted.

[wg4-NDT-j4] S. Lagüela-López, M. Solla-Carracelas, L. Díaz-Vilariño, Julia Armesto-González, “Inspection of radiant heating floor applying non-destructive testing techniques: GPR AND IRT,” DYNA, vol. 82(190), pp. 221-226, March-April 2015; doi: 10.15446/dyna.v82n190.43913 (Spain; OPEN ACCESS)

Abstract: The inspection of radiant heating floors requires the use of non-destructive techniques, trying to minimize inspection impact, time and cost, and maximize the information acquired so that the best possible diagnosis is given. With this goal, we propose the application of infrared thermography (IRT) and ground penetrating radar (GPR) for the inspection of radiant heating floors with different floor coatings, in order to evaluate the capabilities and information acquirable with each technique. Specifically, two common floor coatings have been inspected: ceramic tiles and parquet flooring. Results show that each technique provides different information: condition of the pipelines (IRT), geometry and configuration (GPR), concluding that the optimal inspection is constituted by the combination of the two techniques.

[wg4-NDT-j3] S. Santos-Assunçao, V. Perez-Gracia, O. Caselles, J. Clapes, and V. Salinas, “Assessment of Complex Masonry Structures with GPR Compared to Other Non-Destructive Testing Studies,” Remote Sensing, vol. 6(10), pp. 8220-8237, August 2014; doi:10.3390/rs6098220 (Spain; OPEN ACCESS)

Abstract:  Columns are one of the most usual supporting structures in a large number of cultural heritage buildings. However, it is difficult to obtain accurate information about their inner structure. Non-destructive testing (NDT) methodologies are usually applied, but results depend on the complexity of the column. Non-flat external surfaces and unknown and irregular internal materials complicate the interpretation of data. This work presents the study of one column by using ground-penetrating radar (GPR) combined with seismic tomography, under laboratory conditions, in order to obtain the maximum information about the structure. This column belongs to a “Modernista” building from Barcelona (Spain). These columns are built with irregular and fragmented clay bricks and mortar. The internal irregular and complex structure causes complicated 2D images, evidencing the existence of many different targets. However, 3D images provide valuable information about the presence and the state of an internal tube and show, in addition, that the column is made of uneven and broken bricks. GPR images present high correlation with seismic data and endoscopy observation carried out in situ. In conclusion, the final result of the study provides information and 3D images of damaged areas and inner structures. Comparing the different methods to the real structure of the column, the potential and limitations of GPR were evaluated.

[wg4-NDT-j2] M. Solla, S. Lagüela, H. González-Jorge, and P. Arias, “Approach to identify cracking in asphalt pavement using GPR and infrared thermographic methods: Preliminary findings,” Elsevier Non Destructive Testing and Evaluation (NDT&E) International, vol. 62, pp. 55-65, March 2014; dx.doi.org/10.1016/j.ndteint.2013.11.006 (Spain)

Abstract: Pavement condition is a factor of major interest due to its direct contribution to safety and comfort of the users of the road. Consequently, road inspections imply the evaluation of different parameters such as roughness of the pavement, skid resistance, and presence and condition of cracks. Although the first two parameters can be quantitatively evaluated with different sensors, the latter is usually only qualitatively assessed by visual inspection. This paper deals with this drawback through the combined application of Ground Penetrating Radar and Infrared Thermography to the detection and characterization of cracks in pavement and their origins.

[wg4-NDT-j1] J. Domitrović, T. Rukavina, “Application of GPR and FWD in assessing pavement bearing capacity,” Romanian Journal of Transport Infrastructure, vol. 2(2), pp. 11-21, December 2013; ISSN 2286-2218 ISSN-L 2286-2218 (Croatia; OPEN ACCESS)

Abstract: The process of pavement maintenance and rehabilitation starts by collecting the data which will form the base for evaluation of pavement functional and structural condition. Collection of data can be performed by destructive and non-destructive testing. Usually preferred are the non-destructive methods, that do not damage the pavement, and the process of pavement evaluation is objective and repeatable. Non-destructive testing methods are becoming more and more popular, especially for assessing the structural condition of the pavement. Non-destructive testing by a Falling Weight Deflectometer (FWD) and the analysis of so collected data by the process of backcalculations is today the usual tool for assessing pavement bearing capacity. One of the basic input parameters for analysis of the data collected by FWD is pavement layers thickness. The practice in Croatia is to determine pavement layers thickness by coring. This destructive method affects pavement integrity, so the number of such tests should be kept to the minimum. By coring the accurate thickness of all pavement layers is obtained on specific point locations. Thus, numerous deviations in layer thickness remain unnoticed, and in the end, use of such data for the process of backcalculations does not provide ac urate values of layer moduli. Coring can be replaced with non-destructive method of testing by Ground Penetrating Radar (GPR), which provides continuous information on thickness of all pavement layers. The paper shows the method for assessing the bearing capacity of the pavement based on the data collected by FWD, GPR and coring. The calculation for layer moduli was performed by the ELMOD software, separately for the layers thickness data obtained by coring, and separately for the thickness obtained by GPR tests. Analysis and comparison of the results of calculated elasticity moduli obtained by using various methods for collecting layer thickness data were performed in the paper.