Studying the Construction of Floor Mosaics in the Roman Villa of Pisões (Portugal) Using Noninvasive Methods: High-Resolution 3D GPR and Photogrammetry

Abstract

Over the past decade, high-resolution noninvasive sensors have been widely used in explorations of the first few meters underground at archaeological sites. However, remote sensing actions aimed at the study of structural elements that require a very high resolution are rare. In this study, layer characterization of the floor mosaic substrate of the Pisões Roman archaeological site was carried out. This work was performed with two noninvasive techniques: 3D ground penetrating radar (3D GPR) operating with a 1.6 GHz central frequency antenna, which is a very high-resolution geophysical method, and photogrammetry with imagery obtained by an unmanned aerial vehicle (UAV), which is a very high-resolution optical method. The first method allows penetration up to 30-40 cm depth and 3D models can be obtained, and with the second method, very high detail surface images and digital surface models can be obtained. In this study, we analyze a combination of data from both sensors to study a portion of the floor mosaic of the Pisões Roman Villa (Beja, Portugal) to obtain evidence of the inner structure. In this context, we have detected the main structural levels of the Roman mosaic and some internal characteristics, such as etched guides, internal cracking, and detection of higher humidity areas. The methodology that we introduce in this work can be referenced for the documentation of ancient pavements and may be used prior to carrying out preservation activities. Additionally, we intend to show that a Roman mosaic, understood as an archaeological structure, does not consist of only beautiful superficial drawings defined by the tesserae, but these mosaics are much more complex elements that must be considered in their entirety for preservation.

From Its Core to the Niche: Insights from GPR Applications

“…Although there are few examples, GPR has also provided promising results in monitoring the state of conservation of works of art, such as to evaluate the adhesion between different layers and moisture in paintings and frescoes [104] and stratigraphy and water content in mosaics [105,106].…”

Studying the Water Supply System of the Roman Villa of Pisões (Beja, Portugal) Using Ground-Penetrating Radar and Geospatial Methods

“…In 2017, several geophysical surveys have been carried out with different methods to prospect the subsurface and assess the state of conservation of some structures. Between 2018 and 2020 was carried out a magnetic survey (vertical gradient mode) and groundpenetrating radar (GPR) in several sectors around the pars urbana (Figure 2) [14][15][16]. In the context of this work, we would like to know how the water supply and its distribution for the hydraulic elements of the villa were articulated.…”

Joint Investigation with Ground Penetrating Radar and Infrared Thermography as a Diagnostic Support for the Restoration of Two Wall Mosaics in the Church of St. Mary of the Admiral in Palermo, Italy

“…In fact, these techniques allow the increase of knowledge of the transformations that may have affected historical structures over the centuries, thus supporting and guiding restoration projects [24][25][26][27][28][29][30]. To minimize interpretative ambiguities, the joint use of different noninvasive techniques has often been proposed such as ground penetrating radar (GPR), terrestrial laser scanning (TLS) and infrared thermography (IRT) [31], unmanned aerial vehicle (UAV) photogrammetry and TLS [32], UAV photogrammetry and GPR [33], GPR, and electrical resistivity tomography (ERT) [34,35], GPR, IRT, and ERT [36].…”