Options
Ligas, Paola
Loading...
23 results
Now showing 1 - 10 of 23
- PublicationRestrictedEXPERIMENTAL APPLICATION OF 3-D TERRESTRIAL LASER SCANNING AND ACOUSTIC TECHNIQUES IN ASSESSING THE QUALITY OF STONES USED IN MONUMENTAL STRUCTURES(2007-10-14)
; ; ; ; ;Casula, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Fais, S.; Dipartimento di Geoingegneria e Tecnologie Ambientali - University of Cagliari – Cagliari (Italy) ;Ligas, P.; Dipartimento di Geoingegneria e Tecnologie Ambientali - University of Cagliari – Cagliari (Italy) ;Mora, P.; Dipartimento di Scienze della Terra e Geologico-Ambientali – University of Bologna (Italy; ; ; ; Hellenic Society for NDTThis paper briefly describes the preliminary results of an experimentation aimed to test a new non-destructive methodology based on the integrated application of 3-D terrestrial laser scanning and acoustic techniques in the ultrasonic range (54 kHz) in evaluating the quality of stone materials. Our target is to evaluate the state of conservation of stone building materials by correlating ultrasonic longitudinal pulse velocity and frequency spectra with the reflectivity or reflectance of the reflected 3-D laser scanner beam pulse transmitted to the target of an investigated surface.195 27 - PublicationOpen AccessThree-dimensional imaging from non-destructive techniques in the characterization of stone building materials(EGU - Copernicus, 2018-04-11)
; ; ; ; ; ; ; ; ; ; ; The acquisition of 3D data by means of different methodologies on architectural monumental structures when combined can highlight with efficiency the characteristics of the stone building materials. The result is a threedimensional imaging of different physical properties that can be analyzed and interpreted more objectively and accurately than the conventional two-dimensional ones. We have applied various three-dimensional non-destructive techniques to produce data that can better visualize and detect defects in the shallow and inner parts of the architectural elements built with stone materials. The 3D data volume of a different nature provides a less ambiguous image of the materials and contributes in efficiency by increasing both fidelity and resolution in the diagnostic process. In this paper, we combined high resolution Digital Color Images (DCI) and Terrestrial Laser Scanner (TLS) data for a dense 3D reconstruction of an ancient pillar in a monument of the town of Cagliari, Italy. The TLS technique was supported by a digital photogrammetry survey in order to obtain a natural color texturized 3D model of the study pillar. The 3D model was built with a specific software aligning and combining a set of 2D high resolution color images captured all around the investigated architectural element from multiple viewpoints using a normal handheld 2D digital reflex camera. Final high resolution natural color 3D model reproduces a faithful metrically –correct-scale copy of the analyzed structure and therefore can be effectively compared with the surface geometric anomalies and reflectivity values obtained by the TLS. During the TLS survey we operated a Leica HDS-6200 long-range phase shift terrestrial laser scanner in order to compute an aggregated 3D cloud representing the pillar surface texturized with its reflectivity and the position of the pixels in an intrinsic reference system. Geometrical anomaly maps showing interesting analogies were computed either from the 3D model derived from the TLS application or from the high resolution 3D model detected with the photogrammetry. Starting from the 3D reconstruction from previous techniques an acoustic tomography in an sector of prior interest of the investigated architectural element was carried out. Travel time of longitudinal elastic waves were measured along a great number of measurement paths between stations located on the perimeter of the investigated sections. Each station was alternatively used as transmitter and receiver and measurements of paths crossing the section in a large number of different directions were carried out. Each ray between stations divided in small segments, each corresponding to a pixel element. Inversion techniques were used to obtain a map of the distribution of the longitudinal wave velocity across the sections, thanks to specific software exploiting appropriate reconstruction algorithms. The ultrasonic tomography proved to be an effective tool for detecting internal decay or defects, locating the position of the anomalies and estimating their sizes, shapes, and characteristics in terms of elastic-mechanical properties. Finally, the combination of geophysical and petrographical data sets represents a powerful method for understanding the quality of the building stone materials in the shallow and inner part of the investigated architectural structures.74 7 - PublicationOpen AccessHigh Resolution 3D modelling of Cylinder shape bodies applied to 1000 ancient AD columns(EGU - Copernicus, 2020-05-08)
; ; ; ; ; ; ; ; ; A multi-technique high resolution 3D modelling is described here aimed at the investigation of the state of conservation of carbonate columns of the 1000 BC ancient church of Buon Camino located in the homonymous district of the town of Cagliari (Italy). The integrated application of different Non-Destructive Testing (NDT) diagnostic methods is of paramount importance to locate damaged parts of the building material of artefacts of historical buildings and to plan their restoration. In this study a multi-step procedure was applied starting with a high resolution 3D modelling performed with the aid of Structure from Motion (SfM) Photogrammetry and Terrestrial Laser Scanner (TLS) methodologies. For this delicate task we operated simultaneously a Nikon D-5300 digital Reflex 24.2 Mega pixel Camera and a Leica HDS-6200 Terrestrial Laser Scanner. Subsequently, starting from the information detected with the above methods deeper material diagnostics was performed by means of high resolution 3D ultrasonic tomography aimed at the capillary definition of the elastic properties in the inner parts of the building materials. Measurements of longitudinal wave velocity from ultrasonic data were performed using the transmission method, namely two piezoelectric transducers coupled on the opposite sides of the investigated columns. The ultrasonic data acquisition was planned designing an optimal survey and providing a very good spatial coverage of the investigated columns. The columns were then criss-crossed by a large number of ray paths forming a dense 3D net. The SIRT (Simultaneous Iterative Reconstruction Tomography) algorithm was used to produce the 3D rendering of the velocity distribution inside the investigated columns. With this method the damaged parts were located and it was possible to distinguish them from the unaltered areas. The information on the superficial material conditions obtained by SfM and TLS techniques were compared and integrated with the information of the inner materials obtained by 3D ultrasonic tomography. The results of the above non invasive geophysical techniques have been interpreted in the light of the different textural and petrophysical features of the study carbonate building materials. The study of the main textural features, such as the relationship between bioclasts, carbonate matrix, or that of the cement and petrophysical characteristics such as the nature and distribution of porosity were found to be of fundamental importance in the interpretation of the geophysical data (e.g. TLS reflectance and longitudinal acoustic wave propagation). Therefore a detailed analysis of the textures and pore microstructure were carried out from petrographic thin-sections in Optical and Scanning Electron Microscopy (OM/SEM). The final result of our multi-step-technique integrated methodology is a sophisticated 3D model with a high resolution 3D image representing the internal and external parts of the investigated columns in order to account for their static load resistance and possibly plan their conservation and restoration. The described procedure can also be applied to other cases in which a diagnosis is needed of the state of conservation of the variously shaped, layered-stones and composed artefacts typical of ancient historical buildings.91 16 - PublicationOpen AccessAn integrated petrophysical-geophysical approach for the characterization of a potential caprock-reservoir system for CO2 storage.(EGU - Copernicus, 2016-04-20)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; The selection of a CO2 geologic storage site requires the choice of a study site suitable for the characterization in order to create a robust experimental database especially regarding the spatial petrophysical heterogeneities and elasto-mechanical properties of the rocks that make up a potential caprock-reservoir system. In our study the petrophysical and elasto-mechanical characterization began in a previously well drilled area in the northern part of the Sulcis coal basin (Nuraxi Figus area - SW Sardinia - Italy) where crucial geologic data were recovered from high-quality samples from stratigraphic wells and from mining galleries. The basin represents one of the most important Italian carbon reserves characterized by a great mining potential. In the study area, the Middle Eocene - Lower Oligocene Cixerri Fm. made up of terrigeneous continental rocks and the Upper Thanetian - Lower Ypresian Miliolitico Carbonate Complex in the Sulcis coal basin have been identified respectively as potential caprock and reservoir for CO2 storage. Petrophysical and geophysical investigations were carried out by a great number of laboratory tests on the core samples and in situ measurements on a mining gallery in order to characterize the potential caprock-reservoir system and to substantially reduce geologic uncertainty in the storage site characterization and in the geological and numerical modelling for the evaluation of CO2 storage capacity. In order to better define the spatial distribution of the petrophysical heterogeneity, the seismic responses from the caprock-reservoir system formations were also analysed and correlated with the petrophysical and elasto-mechanical properties In a second step of this work, we also analysed the tectonic stability of the study area by the integrated application of remote-sensing monitoring spatial geodetic techniques. In particular, the global positioning system (GPS) and interferometric synthetic aperture radar (inSAR) were considered useful tools to test the tectonic stability of the storage site. We computed the crustal strain rate of the Sulcis basin starting from the horizontal and vertical velocities detected by applying the two above remote sensing techniques. At the beginning we calculated the Eurasian intra-plate velocity and position time series of some good quality permanent GPS sites present in the study area. We then compared the computed GPS height variation of these sites with the line of sight (LOS) component of InSAR permanent scatters time series detected with the aid of the small baseline (SBAS) method and located closer to the GPS stations. The horizontal components show insignificant residual intra-plate velocities ranging between 0-1 mm/y, while the vertical velocities are comprised between 0 to 2 mm/y, testifying to the stability of the area. The same remote techniques mentioned above can be used during and after the injection of the CO2 to monitor the storage site. This remote monitoring option can be effective, cheap and repeatable.75 9 - PublicationOpen AccessCharacterization of rock samples by a high-resolution multi-technique non-invasive approach(© 2018 Copernicus GmbH, 2019-04-11)
; ; ; ; ; ; ; ; ; ; ; ; ; This paper describes a high resolution multi-technique non invasive approach in which three different techniques (photogrammetric, terrestrial laser scanner and acoustic tomography) are integrated with petrographic data for a detailed characterization of rock samples. To study stone materials both outcropping and in depth, with appropriately prepared samples one can make as many measurements as necessary with different techniques. Moreover, some characterization analyses are destructive and there is a limit on the number of samples that can be sacrificed. The samples need to be carefully selected to ensure they are representative of the rock types under study and significant in different fields (e.g. analysis of the degradation of stone building materials, analysis of aquifer, study of natural reservoirs). As a result, analysis made by the above non invasive techniques integrated with petrographical data on the same materials becomes an indispensable source of data. For the characterization of non-invasive rock samples we started a computation of high resolution 3D models of two samples of a different nature, a comenditic pyroclastic rock and a Pietra Forte carbonate rock, using the terrestrial laser scanning (TLS) methodology and digital photogrammetry. Data were collected using a Leica HDS6200 TLS and a Nikon D-300 digital Reflex camera with the necessary conditions of the highest resolution modality, small incidence angles and a high dynamic range (HDR) in the case of digital images. The resulting clouds and images were processed by specific software using a multi-step procedure which starts with the data input and filtering with elimination of defective points, manual data editing, automatic filtering, raw and fine registration with an iterative closest point (ICP) algorithm in a bundle adjustment modality and successive aggregation of all clouds in high resolution 3D models. Finally, the resulting radiometric information available, such as reflectivity maps, high resolution (HR) photogrammetry textured models and patterns of geometrical residuals, were interpreted in order to locate and underline materials anomalies and differences in composition together with a comparison of reflectance and natural colour anomalies with the roughness of surface materials. Starting with the accurate 3D reconstruction from previous techniques, an acoustic tomography on each rock sample was carefully planned and carried out. Travel time of longitudinal elastic waves were measured along a large number of measurement paths between stations located on the perimeter of the investigated samples. Each measurement point was alternatively used as transmitter and receiver. Inversion techniques were used to obtain a map of the distribution of the longitudinal wave velocity across the sections, thanks to specific software exploiting appropriate reconstruction algorithms. Ultrasonic tomography proved an effective tool in detecting internal defects and heterogeneity of the samples, and led to their fine characterization in terms of elastic-mechanical properties. Finally, the integration of the above three geophysical non invasive techniques with petrographical data represents a powerful method for the definition of the heterogeneity of the rocks at a different scale and for calibrating in situ measurements.110 18 - PublicationOpen AccessA Contribution to the Geological Characterization of a Potential Caprock-Reservoir System in the Sulcis Coal Basin (South-Western Sardinia)(2019-11-27)
; ; ; ; ; ; ; ; ; ; ; ; ; The results provided by this study contribute to the geological characterization of a potential caprock-reservoir system for CO2 storage in the experimental area of the mining district of the Sulcis Coal Basin (south-western Sardinia, Italy). The work is aimed to improve the knowledge of the petrographic and petrophysical characteristics of the siliciclastic and carbonate geological formations that make up the potential caprock-reservoir system. Core samples from a number of wells drilled in the study area for mining purposes were analyzed especially for texture and physical properties (longitudinal velocity, density, porosity, and permeability). The preliminary integrated petrographic and petrophysical characterizations indicate that the Upper Paleocene to Early Eocene potential carbonate reservoir is heterogeneous but presents suitable reservoir zones for CO2. A preliminary analysis of the potential caprock siliciclastic lithologies of the Middle Eocene to Lower Oligocene suggests that they appear suitable for CO2 confinement. Finally, to account for the stability of the investigated area, an accurate geodynamical study of south-western Sardinia was carried out using global navigation satellite system and advanced differential interferometric synthetic aperture radar methodologies in order to estimate vertical and horizontal crustal displacements. The study area results stable, since it is characterized by surface crustal horizontal and vertical velocities smaller than 1 mm/year and few mm/year, respectively.962 95 - PublicationOpen AccessThree-dimensional imaging from laser scanner, photogrammetric and acoustic non-destructive techniques in the characterization of stone building materials(2018-07-27)
; ; ; ; ; ; ; ; ; ; ; Abstract. When combined, the three-dimensional imaging of different physical properties of architectural monumen- tal structures acquired through different methodologies can highlight with efficiency the characteristics of the stone building materials. In this work, we compound high res- olution Digital Color Images (DCI) and Terrestrial Laser Scanner (TLS) data for a dense 3-D reconstruction of an ancient pillar in a nineteenth century building in the town of Cagliari, Italy. The TLS technique was supported by a digital photogrammetry survey in order to obtain a natural color texturized 3-D model of the studied pillar. Geometri- cal anomaly maps showing interesting analogies were com- puted both from the 3-D model derived from the TLS ap- plication and from the high resolution 3-D model detected with the photogrammetry. Starting from the 3-D reconstruc- tion from previous techniques, an acoustic tomography in a sector of prior interest of the investigated architectural ele- ment was planned and carried out. The ultrasonic tomogra- phy proved to be an effective tool for detecting internal decay or defects, locating the position of the anomalies and estimat- ing their sizes, shapes, and characteristics in terms of elastic- mechanical properties. Finally, the combination of geophysi- cal and petrographical data sets represents a powerful method for understanding the quality of the building stone materials in the shallow and inner parts of the investigated architectural structures.986 102 - PublicationOpen AccessDiagnostic Process of an Ancient Colonnade Using 3D High-Resolution Models with Non-Invasive Multi Techniques(2023-03-14)
; ; ; ; ; ; ; ; ; Here, an avant-garde study of three ancient Doric columns of the precious, ancient Romanesque church of Saints Lorenzo and Pancrazio in the historical town center of Cagliari (Italy) is presented based on the integrated application of different non-destructive testing methods. The limitations of each methodology are overcome by the synergistic application of these methods, affording an accurate, complete 3D image of the studied elements. Our procedure begins with a macroscopic in situ analysis to provide a preliminary diagnosis of the conditions of the building materials. The next step is laboratory tests, in which the porosity and other textural characteristics of the carbonate building materials are studied by optical and scanning electron microscopy. After this, a survey with a terrestrial laser scanner and close-range photogrammetry is planned and executed to produce accurate high-resolution 3D digital models of the entire church and the ancient columns inside. This was the main objective of this study. The high-resolution 3D models allowed us to identify architectural complications occurring in historical buildings. The 3D reconstruction with the above metric techniques was indispensable for planning and carrying out the 3D ultrasonic tomography, which played an important role in detecting defects, voids, and flaws within the body of the studied columns by analyzing the propagation of the ultrasonic waves. The high-resolution 3D multiparametric models allowed us to obtain an extremely accurate picture of the conservation state of the studied columns in order to locate and characterize both shallow and internal defects in the building materials. This integrated procedure can aid in the control of the spatial and temporal variations in the materials’ properties and provides information on the process of deterioration in order to allow adequate restoration solutions to be developed and the structural health of the artefact to be monitored.346 27 - PublicationOpen AccessCharacterization of Rock Samples by a High-Resolution Multi-Technique Non-Invasive Approach(2019-10-29)
; ; ; ; ; ; ; ; ; Three di erent non-invasive techniques, namely Structure from Motion (SfM) photogrammetry, Terrestrial Laser Scanner (TLS) and ultrasonic tomography integrated with petrographic data, were applied to characterize two rock samples of a di erent nature: A pyroclastic rock and a carbonate rock. We started a computation of high-resolution 3D models of the two samples using the TLS technique supported by a digital SfM photogrammetry survey. The resulting radiometric information available, such as reflectivity maps, SfM photogrammetry textured models and patterns of geometrical residuals, were interpreted in order to detect and underline surface materials anomalies by a comparison of reflectance and natural colour anomalies. Starting from the 3D models from previous techniques, a 3D ultrasonic tomography on each rock sample was accurately planned and carried out in order to detect internal defects or sample heterogeneity. The integration of the above three geophysical non-invasive techniques with petrographical data—especially with the textural characteristics of such materials—represents a powerful method for the definition of the heterogeneity of the rocks at a di erent scale and for calibrating in situ measurements.953 106 - PublicationOpen AccessDiagnostic process of an ancient colonnade using non-invasive volume visualization multi techniques(Copernicus - GMBH, 2022-05-23)
; ; ; ; ; ; ; ; ; The diagnostic process on the cultural heritage by non-invasive multi techniques generates multiple volumes of different data sets. Such volumes can be applied to a whole range of problems from diagnostics of the building stone materials to their in-time monitoring for maintenance and conservation. The results of the diagnostic process in multimodal data sets can be rendered effective by comparing multiple volumes at the same time and over time since the safety of monumental structures requires periodic monitoring. As already shown in recent works that focused on the integration of heterogeneous data from complementary techniques, the use of a single technique is generally insufficient to obtain a reliable diagnostic process. The multi-technique high resolution 3D models described in this paper was aimed to investigate the conservation state of a precious carbonate colonnade in the ancient church of Saints Lorenzo and Pancrazio, dating to about the second half of the thirteenth century and located in the old town of Cagliari (Italy). The diagnostics of the carbonate colonnade was made by 3D non-invasive multi-techniques, i.e. Terrestrial Laser Scanner (TLS), close range photogrammetry (CRP) and ultrasonic tomography supported by petrographic investigations. To obtain a natural colour texturized 3D model of the columns with calibrated scale and coordinates both the TLS and CRP techniques were applied. The geometrical anomaly and reflectivity maps derived from the data of the TLS-CRP survey show presence of some anomalies worthy of attention. The 3D reconstruction with previous techniques was the essential base for the planning and execution of the 3D ultrasonic tomography that played an important role in detecting internal defects and voids and flaws within the materials by analysing the propagation of ultrasonic waves. The results of the non-invasive diagnostic techniques on the building carbonate materials of the ancient colonnade were supported by thin section and mercury intrusion porosimetry (MIP) analyses in order to study their porosity and other textural characteristics such as the grainsmatrix or grains-cement relationships, the bioclasts packing, the pore network and other petrophysical parameters (i.e. permeability and tortuosity). Knowledge of these characteristics is key to understanding the different susceptibility of the building carbonate materials to degradation and recognizing any forms of degradation while providing fundamental support to the interpretation of the geophysical data.46 10
- «
- 1 (current)
- 2
- 3
- »