Knowledge of submerged cultural heritage through high resolution digital photogrammetry

Underwater cultural heritage is an integral part of the human heritage and, as such, attention must be paid to its preservation. If the safety of the assets on land is not guaranteed, for the submerged ones the critical issues are greatly increased. Therefore, it is necessary to collect and analyze data that will enable us to enhance and safeguard these assets in the best possible way. The Archimedes project aims to map, analyze and enhance these assets, in different environments. In this paper some techniques for underwater data collection and analysis using a photogrammetric approach will be shown. Particular attention has been paid to the camera calibration phase, a fundamental part of underwater surveys. Different softwares ware used, which allowed to do direct comparisons. It was also evaluated which type of data is best to minimize the presence of distortions. Another analysis that has been addressed is that of radiometric calibration of the data. The depth at which the submerged asset is located is closely related to the presence of light, and this affects both the data acquisition phase and the processing phase. The processed data are part of two different datasets. The first one was acquired at Coluccia Island (Sardinia), and the second one was acquired at Porto Cesareo (Apulia). Both datasets were acquired in shallow water. As a final analysis, the calibration of images acquired with a new dual-camera system with the presence of a dome was done to reduce the presence of distortions in the data acquisition phase. It is important to remember that the underwater heritage is part of our history and culture and it is our duty to safeguard it, but not only that. The Archimedes project aims not only to analyze these assets, but also to make them accessible to underwater and non-underwater tourism, through means such as virtual reality. In this way, the entire heritage, which is accessible to those with specific expertise, is made reachable to a much wider audience