Casula, Giuseppe

The research scope of the papers published in this Special Issue mainly focuses on high-precision and high-reliability positioning, navigation, and timing (PNT) with Global Navigation Satellite System (GNSS) or multi-source sensors, resilient PNT with GNSSs or multi-source sensors in challenging environments, integrated PNT with GNSSs and multi-sensor systems, applications of PNT with GNSSs or multi-source sensors, etc.

Abstract: Non-invasive techniques, such as close-range photogrammetry (CRP) and 3D ultrasonic tomography complemented with optical and scanning electron microscopy and mercury porosimetry, were applied to characterize the carbonate rock samples of the Calcari di Cagliari formation. The integrated approach started with the computation of high-resolution 3D models of the carbonate samples using the CRP technique to produce 3D high-resolution models texturized both with natural colors and intensity. 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 the elastic properties of such rocks and relate them to textural heterogeneity or internal defects. The results indicate that the relationship between longitudinal velocity and rock properties is complex even in the same carbonate formation. Understanding the relationship between the geomatic and geophysical responses in the investigated rock properties, such as textural characteristics and especially structure and geometry of pores, type of pores, tortuosity and cementing material, is important for many practical applications and especially in the diagnostic process of the conservation state of monumental structures. The integration of the above non-invasive techniques complemented by petrographical–petrophysical data proved to be a powerful method to associate each lithotype with a different susceptibility to degradation. The results presented in this paper demonstrate that the proposed integrated use of complementary methodologies would guarantee the reproducibility of the measurements both at the laboratory and field scale for the monitoring in time of the rock condition while giving a useful contribution in making decisions on an appropriate remedial strategy.

The integrated use of non-destructive geomatic and geophysical techniques such as close-range digital photogrammetry, laser scanner techniques, thermography, sonic and ultrasonic methods, resistivity, etc... for the diagnostics of the stone building materials of architectural structures has become increasingly dependent on the integration of different disciplines of applied research. As is well known many historic monuments are characterized by severe damage due to temporal degradation, problems caused by differential settlements of the foundations and various types of natural hazards. Therefore it is of great interest to test and develop effective, integrated non invasive procedures to detect the conservation state of the building materials of historic structures, and identify and prevent their potential vulnerability in order to preserve their intrinsic characteristics for a long time. For extensive applications, as well as for investigations on monuments or large architectural elements, scanning and digital high resolution images are particularly useful, thanks to their limited cost, high production and relatively simple reproducibility of the tests. These techniques give useful information on the shallow conditions of the investigated materials. Geophysical techniques such as the ultrasonic and resistivity methods are non-invasive and are considered the most appropriate to evaluate the internal structure and assess the quality of the stone materials of the architectural heritage. This paper presents an integrated approach that combines advanced geomatic survey procedures, such as close-range photogrammetry (CRP) based on high resolution images and Terrestrial Laser Scanner (TLS) techniques with a few geophysical techniques such as the ultrasonic and resistivity ones in order to test the effectiveness of the integrated approach in providing an effective diagnosis of stone building materials in the Basilica di San Saturnino (Cagliari – Italy). This Basilica is the oldest monument of the town of Cagliari (Italy) and represents an interesting synthesis of different construction techniques with heterogeneous stone materials of different origins. CRP and TLS were applied to the investigated elements with the aim of obtaining a natural colour texturized 2D-3D model with a calibrated scale and coordinates. The geometrical anomaly and reflectivity maps derived from the data of the CRP-TLS survey show the presence of some anomalies worthy of attention, but they were referred to the shallow materials. A further investigation on site using the ultrasonic pulse velocity (UPV) and electrical resistivity techniques were performed to investigate the materials in depth. The results of the CRP and TLS techniques allowed the best design of the ultrasonic and electrical techniques and also proved to be useful in the data interpretation phase.

The methods and the tools aimed at characterizing and analysing the carbonate materials used in the historic built heritage often follow different ways according to the different branches of applied research involved in the knowledge process. In this framework, the 3D digital models both of in situ architectural elements and of significative samples of rocks used as building materials can play an important role in relating different data and disciplines aimed at the prevention and conservation of the Cultural Heritage. Although the 3D geomatic and geophysical digital models represent privileged tools of the diagnostic analysis, they must be supported by the knowledge of the textural characteristics of the rocks under investigation with petrographic analyses. In order to study the stone materials heavily used in the historic built heritage and analyse their vulnerability to the conditions in their environment, it can be beneficial to study appropriately prepared samples and make as many measurements as necessary with different techniques. Moreover, some analyses are destructive and there is a limit to the number of samples that can be sacrificed. For this reason, in the analysis of rock samples, non-destructive techniques are constantly being improved. In this study, using a suitably implemented integrated methodology we analysed in detail samples of the carbonate rocks of the Calcari di Cagliari formation represented by Pietra Cantone, Tramezzario and Pietra Forte lithologies, mainly used in the past as construction materials for the buildings of the Historical Centre of Cagliari (Italy). Our methodology is represented by an integration of the geomatic survey carried out by structure-from-motion (SfM) digital close-range photogrammetry and the seismic tomography normally used for the in situ inspection adapted to laboratory tests on samples of the above lithologies using ultrasonic frequency signals. The rigorous metric of the geomatic 3D models was used to implement the ultrasonic survey by which internal characteristics and physical properties of the studied material are detected thanks to the spatial variations of the longitudinal velocity obtained after the tomographic inversion. The geomatic and geophysical data were complemented by an accurate analysis of the above carbonate materials by optical and scanning electron microscopy in order to detect their textural characteristics and especially the nature and distribution of their porosity. The microscopy analyses were integrated by mercury intrusion porosimetry (MIP) to obtain further information on the pore network, particularly on the effective porosity, pores-throat diameters/radii, permeability and tortuosity of the investigated materials. All the above parameters were found to affect the geomatic and geophysical behaviour of the carbonate materials. The integration of the multi-technique data produced in this study contributes to better understand the interaction between the investigated materials and the environment.

The Global Navigation Satellite System (GNSS) can provide users with high-precision positioning information continuously and benefits all walks of life, e.g., unmanned driving, urban navigation, deformation monitoring, etc. The important scientific research and application value of GNSSs have prompted many countries and regions to develop GNSS technologies. GNSS core positioning technologies, such as Precise Point Positioning (PPP) and Real-Time Kinematic positioning (RTK), can provide decimeter-level or even centimeter-level positioning accuracy in open environments. However, active GNSS positioning technologies are susceptible to complex conditions, including canyon environments, low-cost receivers, and multi-GNSS situations, and, on occasion, cannot provide accurate, continuous, and reliable positioning information. The diversification of GNSS systems and constellations, receiver types, and observation environments puts forward higher requirements for technology and algorithms to maintain high-precision positioning and navigation services. Advanced algorithms are key to solving GNSS practical application problems and expanding the scope of GNSS applications. This Special Issue aims at studies covering improved methods and the latest challenges in precise GNSS positioning and navigation, especially under complex conditions for various research investigations as well as a range of practical applications. Both theoretical and applied research contributions to the GNSS high-precision technology in all disciplines are considered. Topics may cover anything from precise muti-GNSS positioning algorithms and GNSS data processing to more comprehensive targets and scales. Therefore, new algorithms for high-precision positioning and navigation, GNSS receivers, software development for data collection and processing, and their applications in various fields are all included.

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.

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.

Abstract: This study presents the integrated application of a few non-destructive techniques, i.e., Close Range Photogrammetry (CRP), and low frequency (24 kHz) ultrasonic tomography complemented by petrographical analysis. The aim here is to assess the conservation state of a Carrara marble column in the Basilica of San Saturnino, which is part of a V-VI century Palaeo Christian complex in the city of Cagliari (Italy). The high resolution 3D modelling of the studied artifact was computed starting from the integration of proximal sensing techniques, such as CRP based on the Structure from Motion (SfM) technique, which provided information on the geometrical anomalies and reflectivity of the investigated marble column surface. The inner parts of the studied body were inspected successfully in a non-invasive way by computing the velocity pattern of the ultrasonic signal through the investigated materials, using 3D ultrasonic tomography. The latter was optimally designed based on the 3D CRP analysis and the locations of the source and receiver points were detected as accurately as possible. The integrated application of in situ CRP and ultrasonic techniques provided a full 3D high resolution model of the investigated artifact, which made it possible to evaluate the material characteristics and its degradation state, affecting mainly the shallower parts of the column. The 3D visualisation improves the efficiency, accuracy, and completeness of the interpretative process of data of a different nature in quite easily understood displays, as well as the communication between different technicians.

The diagnosis of the conservation state of monumental structures from constraints to the spatial distribution of their physical properties on shallow and inner materials represents one of the key objectives in the application of non-invasive techniques. In situ, CRP and 3D ultrasonic tomography can provide an effective coverage of stone materials in space and time. The intrinsic characteristics of the materials that make up a monumental structure and affect the two properties (i.e., reflectivity, longitudinal velocity) through the above methods substantially differ. Consequently, the content of their information is mainly complementary rather than redundant. In this study we present the integrated application of different non-destructive techniques i.e., Close Range Photogrammetry (CRP), and low frequency (24 KHz) ultrasonic tomography complemented by petrographycal analysis based essentially on Optical Microscopy (OM). This integrated methodology has been applied to a Carrara marble column of the Basilica of San Saturnino, in Byzantine-Proto-Romanesque style, which is part of the Paleo Christian complex of the V-VI century. This complex also includes the adjacent Christian necropolis in the square of San Cosimo in the city of Cagliari, Sardinia, Italy. The column under study is made of bare material dating back probably to the first century A.D., it was subjected to various traumas due to disassembly and transport to the site, including damage caused by the close blast of a WWII fragmentation bomb. High resolution 3D modelling of the studied artifact was computed starting from the integration of proximal sensing techniques such as CRP based on Structure from Motion (SfM), with which information about the geometrical anomalies and reflectivity of the investigated marble column surface was obtained. On the other hand, the inner parts of the studied body were successfully inspected in a non-invasive way by computing the velocity pattern of the ultrasonic signal through the investigated materials using 3D ultrasonic tomography. This technique gives information on the elastic properties of the material related with mechanical properties and a number of factors, such as presence of fractures, voids, and flaws. Extracting information on such factors from the elastic wave velocity using 3D tomography provides a non-invasive approach to analyse the property changes of the inner material of the ancient column. The integrated application of in situ CRP and ultrasonic techniques provides a full 3D high resolution model of the investigated artifact. This model enhanced by the knowledge of the petrographic characteristics of the materials, improves the diagnostic process and affords reliable information on the state of conservation of the materials used in the construction processes of the studied monumental structure. The integrated use of the non-destructive techniques described above also provides suitable data for a possible restoration and future preservation.

A field-integrated methodology using 3D ultrasonic tomography supported by close range photogrammetry (CRP) has been developed and evaluated as a tool to detect the presence and patterns of decay forms in a living adult holm oak (Quercus ilex L.) in an urban green area of the city of Cagliari, Sardinia, Italy. Close range photogrammetry was used to compute a high resolution 3D model of the studied tree, texturized with natural colors. Moreover, following the implemented workflow process it was possible to evaluate the deformation pattern of the studied tree over time. In a second step of our integrated approach, and in order to diagnose the state of health of the inner part of the studied tree in a non-invasive way, laboratory and in situ non-invasive ultrasonic techniques were applied. The results of the close range photogrammetry analysis supported the optimal design of the 3D ultrasonic tomography of the living adult holm oak. Ultrasonic tomography is one of the most powerful non-destructive testing techniques for the full-volume inspection of a structure. It produced physical information on the inner structure of the stem of the investigated tree. The results of the study show that the integrated application of close range photogrammetry and 3D ultrasonic tomography is a powerful tool for a highly accurate and objective evaluation of the external and internal decay of trees and for monitoring their conservation states. With the fully integrated approach, the diagnostic process aimed to prevent instability and the failure of trees can be greatly improved.