Photogrammetric techniques for digitalization of underwater cultural assets: The case study of the Torre Santa Sabina’s Shipwreck

Underwater cultural sites are, for their intrinsic nature, among the most difficult-to-reach heritage. The difficulty of operating in underwater environments derives not only from the reduced stay time of the operator on the site but also to environmental condition that might affect the survey (such as light condition, turbidity of the water, etc.) reducing its overall quality. The possibility offered nowadays by the adoption of digital photogrammetry techniques allows one to virtually reconstruct the surveyed underwater assets to make it accessible also remotely, via visualization and dissemination platforms (online or offline). In order to improve the study of the documented cultural heritage artefacts and sites, it is crucial to adopt the right photogrammetric principles, such as carefully planning the acquisition geometry, opportunely calibrating the camera before the final acquisition, correctly acquire the images with satisfying the optimal overlap and sidelap, using metric scale bars and or Ground Control Points in order to achieve 3D metric and georeferenced products that are geometrically consistent and coherent with the real object of the survey. This paper is related to the photogrammetric survey of the late-imperial era roman shipwreck, located in Baia dei Camerini, Torre Santa Sabina (BR), Italy, in the framework of the project UnderwaterMuse (Italia-Croatia 2014-2020 Cooperation Programme). An integrated topographic and photogrammetric (underwater and UAV) survey has been conducted, and in the present research the last advancements in the underwater photogrammetry data acquisition and processing will be addressed in combination with the UAV achievable products. More in detail a focus on camera calibration and quality assessment of the achieved results will be presented.