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.
Highlights
The diagnosis of the conservation state of monumental structures, from the constraints to the spatial distribution of their physical properties on shallow and inner building materials, represents one of the key objectives in the application of non-invasive techniques.In the field of cultural heritage, the complex task of the diagnostics of the state of conservation of ancient monuments is a topic that involves many subjects, such as public and private institutions, civil protections, etc
The economic aspect is to be taken into account, since the monitoring and intervention for the maintenance of monumental structures often require the outlay of important financial resources [1,2]
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 petrographical analysis, which is based on Optical Microscopy (OM)
Summary
The diagnosis of the conservation state of monumental structures, from the constraints to the spatial distribution of their physical properties on shallow and inner building materials, represents one of the key objectives in the application of non-invasive techniques. The higher spatial and spectral resolutions of sensors available for SfM photogrammetry improve the diagnostic analysis, especially in the knowledge phase They facilitate the monitoring of the conservation state of monumental structures, allowing for the attainment of natural colour in-time (time-lapse) texturized 3D models. The CRP technique plays a fundamental role in the planning and interpretation phases of 3D ultrasonic tomography, providing 3D high resolution measurable models on which to carry out a huge quantity of measurements (e.g., precise locations of the source and receiver points), which is indispensable in rendering the 3D ultrasonic data at their precise location This integrated methodology has been applied to a Carrara marble column in the Basilica of San Saturnino (Figure 1a,b), called the Church of Saints Cosma and Damiano, in Byzantine-Proto-Romanesque style, which is part of the Palaeo-Christian complex of the V-VI century.
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