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Byline: Giuseppe Casula, Silvana Fais, Paola Ligas This paper briefly describes the preliminary results of an experiment that aimed to test a new nondestructive methodology based on the integrated application of Three-Dimensional (3D) 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 materials by correlating ultrasonic longitudinal pulse velocity and frequency spectra with the reflectivity or reflectance of the reflected 3D Laser Scanner (LS) beam pulse transmitted to a part of an investigated surface.

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. [ABSTRACT FROM AUTHOR]

Due to recent human activity many holm oak trees (Quercus ilex L.) are planted in the public and private gardens in Sardinia. At present many of these trees are afflicted by decay especially that caused by pathogenic fungi which produce tail disease and bark cancer. A field methodology using ultrasonic tomography supported by a digital photogrammetry survey has been developed and evaluated as a tool to detect the presence and patterns of internal decay in a living adult holm oak tree. Ultrasonic methods are commonly used to detect the elastic characteristics and thus the dynamic properties of different materials (e.g. stone, concrete, wood) although the interpretation of the data is very complex because elastic wave propagation strictly depends on the heterogeneity, the porosity and other material properties. Weak materials, the presence of fractures or decay zones, small cavities, and cracks within the materials are potential defects characterized by low ultrasonic velocity compared to the velocity in healthy materials. In this sense, ultrasonic velocity can be used effectively as one of the main diagnostic physical parameters to detect internal decay and define the healthy state of the investigated holm oak stem with diameter at breast height (DBH) of 32 cm. In this study, considering the nature and size of the investigated tree and the target of the study, an ultrasonic investigation by the three-dimensional ultrasonic tomography technique was carried out at 24kHz. The ultrasonic measurements were performed in situ using the portable ultrasonic non-destructive digital indicating tester (PUNDIT Lab plus) by Proceq (Schwerzenbach, Switzerland) and piezoelectric transducers. Silicone snug sheets were chosen as the coupling agent because they provided the best contact transducer material as deduced from many tests.The travel time of the longitudinal elastic waves was measured along a large number of measurement paths between stations located on the perimeter of the stem. Each station was alternatively used as a transmitter and a receiver. The sector of the stem was criss-crossed by a large number of discrete rays. Each ray between stations was divided into small segments, each corresponding to a pixel element. The travel time of the longitudinal ultrasonic signals along the source-receiver ray paths was recorded together with the relative position and orientation of each ray. The ultrasonic data volume was processed by specific software exploiting appropriate reconstruction algorithms to obtain a three-dimensional representation of the distribution of the longitudinal wave velocity inside the stem. Results show that ultrasonic tomography may be an effective tool for a high accuracy evaluation of the internal decay of the investigated tree and for monitoring its conservation state.KEY WORDS: Holm oak, ultrasonic tomography, decay detection, monitoring. [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]