Search

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. [ABSTRACT FROM AUTHOR]

Rock-carved cultural heritage sites are often developed in slopes formed by weak rocks, which due to their peculiar lithological, geotechnical, and morpho-structural features are characterized by excellent carvability, which at the same time makes them prone to weathering, deterioration, and slope instability issues. In this context the use of advanced close-range nondestructive techniques, such as Infrared Thermography (IRT) and Unmanned Aerial vehicle-based Digital Photogrammetry (UAV-DP) can be profitably used for the rapid detection of conservation issues (e.g., open fractures, unstable ledges-niches, water seepage and moisture) that can lead to slope instability phenomena. These techniques, when combined with traditional methods (e.g., field surveys, laboratory analysis), can provide fundamental data (such as 3D maps of the kinematic mechanisms) to implement a site-specific and interdisciplinary approach for the sustainable protection and conservation of such fragile cultural heritage sites. In this paper some examples of conservation problems in several rupestrian sites characterized by different geological contexts, from the mountainous regions of Georgia to the ancient city of Petra in Jordan, are presented, with the aim of evaluating the potential of the proposed integrated approach. The final aim is to provide conservators, practitioners, and local authorities with a useful, versatile, and low-cost methodology, to be profitably used in the protection and conservation strategies of rock-carved sites. [ABSTRACT FROM AUTHOR]

Three different 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 different 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 different scale and for calibrating in situ measurements. [ABSTRACT FROM AUTHOR]

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.Key words: Terrestrial laser scanner, photogrammetric technique, 3D ultrasonic tomography, stone samples. [ABSTRACT FROM AUTHOR]

A combination of digital photogrammetry and Global Positioning Systems (GPS) surveying has been used to measure landslide surface displacements and to estimate the volume involved in the movement. Ninety-eight percent of landslides mapped as active in the Emilia-Romagna region of northern Italy are reactivations of dormant mass movements. The Ca'' di Malta landslide, south of Bologna, was chosen to test this integrated system. A 0.5-m cellsize Digital Elevation Model (DEM) with vertical accuracy of 0.1 m was generated using digital photogrammetric techniques.We have used a combination of digital photogrammetry and three GPS techniques to monitor landslide movement. Rapid static surveying in which the survey observations are made for a period of minutes yielded sub-centimetre positions for several marked points distributed on a longitudinal axis along the landslide. Kinematic surveying, in which the observations are carried out continuously, in this case by a walking person, provided models of the surface (1×1 m grid) by measuring the position of irregularly distributed points. Continuous observations over 7 months were made between two GPS receivers. One positioned within the moving landslide body and the other at a fixed location outside the landslide. An automatic procedure was developed to download, process and compute relative movement at constant time intervals. The accuracy achieved with the GPS measurements ranges between several millimetres to a few centimetres for static and kinematic observations, respectively.This integrated survey technique is a cost-effective method that could be applied to other structural and morphological settings. The real-time monitoring could be coupled with a warning system for landslide hazard management and the repeated kinematic GPS surveys derive precise DEMs of a landslide, providing information on geometry, volumes and evolution of the phenomenon. [Copyright &y& Elsevier]