Diparttimento di Studi Umanistici Universita Ca Foscari Venezia

Image ‘stitching’ technique lets scientists explore shipwrecks from dry land

Shipwrecks and other underwater relics can tell archaeologists a lot about ancient people’s seafaring ways, but investigating these sites can be costly, time-consuming, and dangerous. Now, an inexpensive imaging method is allowing underwater archaeologists to ditch their wetsuits and explore complex, 3D renderings of the briny deep from the safety of dry land. Called multi-image photogrammetry, the process uses underwater cameras and sophisticated computer software to stitch together images and develop extremely accurate virtual dive sites. In a single dive day, the renderings can capture topographic details that would take weeks of manual measurements to record (above). Archaeologists studying ancient shipwrecks recently put this technique through the paces at three different shipwreck sites dated to the second and third centuries C.E. off the coast of Sicily in Italy. The wreck sites are littered with large marble columns and blocks and piles of amphorae—ceramic vats used by ancient people throughout the Roman Republic. By excavating and rephotographing the amphorae layer by layer, the archaeologists preserved a record of the shipwreck’s contents in their original sunken configuration, they report this month in the Journal of Cultural Heritage. And it’s not a purely archival effort: Analyzing 3D renderings of the Marzamemi I, a third century Roman shipwreck site off the coast of Pachino, Sicily, let the researchers accurately gauge the volume of the ship’s cargo of scattered marble blocks and columns. That, in turn, allowed them to estimate the size of the vessel—a freighter between 32 and 40 meters long—offering some of the first evidence of the type of transport ships used in this era.