Geometric and radiometric recording of prehistoric graphic expression: the case of Peña Tu (Asturias, Spain)

Abstract In the studies on Prehistoric Graphic Expression, there are recurrent discussions about the tracings generated by different observers of the same motif. Methodological issues concerning the role of archaeological imaging are often implied within those debates. Do the tracings belong to the observational data exposition chapter, or are they part of the interpretative conclusions? How can the current technological scenario help solve these problems? In 2017, we conducted new documentation of the Peña Tu rock shelter, a well-known site with an intriguing post-palaeolithic graphic collection documented on several occasions throughout the twentieth century. Our objective was to provide quantifiable and, if possible, objective documentation of the painted and engraved remnants on the shelter’s surface. To achieve this, we employed two data capture strategies. One strategy focused on analysing the vestiges of paintings using a hyperspectral sensor, while the other centred on the geometric definition of engravings and the rock support, utilising photogrammetric techniques and laser scanning. These approaches presented various parallax challenges. Despite these challenges, our results were highly satisfactory. We resolved uncertainties regarding the formal features of specific designs that had been subject to debate for a long time. Additionally, we discovered previously unpublished areas with traces of paintings. Lastly, we developed a map highlighting recent alterations and deteriorations, providing a valuable tool for assessing the site’s preservation status. In conclusion, by employing advanced technology and comprehensive documentation methods, we significantly contributed to understanding and preserving the prehistoric graphic expressions at the Peña Tu rock shelter.