Geoposition data aided mosaicing for archeology sites documentation: The islet of Bisaga (Kornati Archipelago) site case

Part of underwater archaeologist's work consists in documentation of underwater sites. This is done by divers, with deployment of markers, poles, grids, etc. over the sea-bottom. Surveys with the traditional techniques require a considerable effort limiting the possibilities of multiple inspection surveys by the responsible agencies. Within the last ten years, ISME (Interuniversity Ctr. Integrated Systems for the Marine Environment) and SBAT (Italian Ministry of Culture, Superintendence of Archaeological Goods of Tuscany - Soprintendenza per i Beni Archeologici di Toscana) have worked toward automation of the survey process. The objective is the development of low-cost, easy-to-use and non-invasive systems to obtain a geo-referenced augmented map of a wreck site. During the VENUS project, funded by European Commission - Information Society Technologies (IST) and ended in 2010, UNIVPM - Università Politecnica delle Marche (ISME) and SBAT has worked together providing scientific methodologies and the technological tools for the virtual exploration of deep underwater archaeological sites. The VENUS project improved the accessibility of underwater sites by generating thorough and exhaustive 2D and 3D records for virtual exploration. UNIVPM's team and SBAT's team, following the work done in VENUS, in the last year (2010), have continued to develop new technologies and have validated techniques with other archaeological institutions. This paper presents the results obtained by UNIVPM's team within the Breaking the Surface 2010 Workshop
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(Murter, Croatia) in studying one famous cultural and historical heritage site in Kornati Archipelago. Several dives made on this site and a program of remote sensing using an AUV and an ROV with a camera was made. In addition to these explorations, a number of finds are been geo-localized and a final map has been created starting from the photomosaic of the sea-bottom. To this aim, different technological components are been developed or integrated, including a still camera for photogrammetric reconstruction of the site and an USBL acoustic positioning system. Crucial to the performance of the automated system has been the integration of the acoustic positioning system with the photo archive in the dive state estimation algorithm, in the design and definition of a specific data format used to store the data; in the geo-referentiation of the estimated position and in the determination of the geometrical features of the site. This positioning data will be effective also in facilitating excavation operations, allowing to focus the diving on the precise spot determined by the archaeologists after the geo-referenced surveys.