Marine Archaeological Surveying Using Snake Robots: The Eely Survey of Figaro Wreck in the High Arctic

The exploration and documentation of underwater archaeological and historical sites have been significantly enhanced by the utilization of marine robotics of various sizes, propulsion capabilities, sensor configurations, and autonomy levels. Highly flexible and articulated underwater vehicles, also referred to as kinematically hyper-redundant robots, have garnered a lot of interest in subsea operations in the last few years, thanks to their high degree of maneuverability and adaptability to the environment they are navigated into. This article presents the integrated photogrammetric mapping of an underwater cultural heritage site using an underwater snake robot for the first time. The snake robot Eely submerged down to the 20th century wreck Figaro , 35 m deep, in Trygghamna fjord, in the Svalbard archipelago. A multidisciplinary team of engineers, marine archaeologists, and surveyors cooperated on this purpose within the wider framework of a shipwreck mapping campaign in the High Arctic. While the snake robot is capable of fully autonomous untethered operations, for this mission, the 6-m-long vehicle was deployed as a remotely operated vehicle so that real-time mapping and online decision-making were feasible. The Eely platform's photogrammetric concept, that is described in detail in the paper, is based on its ability to change shapes depending on the geometry of the object or area of mapping interest. A set of multiple cameras and lights was mounted along the three segments of the articulated robot aiming for visual data acquisition and photogrammetric documentation, while a set of acoustic sensors was used to enhance global situational awareness on the site and provide real-time information about the progress of the mission to the supervising archaeologist through augmented maps. A multibeam echosounder, mounted on the bottom of the middle segment of the robot, allowed for status updates of the site's coverage, while a forward-looking sonar allowed for obstacle avoidance. In this paper, we provide a detailed description of the methodology used for the wreck survey covering each stage from mission planning (mission's scope, definition of sub-tasks, platform and sensors configuration, and design and simulation of the robot's transects over the wreck), to the real-world operations and data acquisition, and, finally, results. We compare our findings with previous missions at the same wreck site, both qualitatively and quantitively, and finally discuss how such innovative technology, like snake robots, can bring marine archaeological mapping to a new level.