Innovative Techniques to Support the Surveying and the Exploration of Underwater Sites by Scientific and Recreational Divers

Abstract

In the submerged environment divers often suffer from low visibility conditions that make difficult the orientation within an underwater site. At present, there is a lack of technologies and tools supporting the divers to better orientate themselves in the underwater environment and to simplify their comprehension of the context. The research aims to design and develop innovative solutions to support divers, both recreative and technical/scientific ones, through a novel system for underwater navigation and exploration, providing them with underwater geo-localization, contextualized information, augmented reality (AR) contents and recommendation about the optimal path to follow during the dive. A first aspect on which the research work focused is the Underwater Image Enhancement. This study has led to the development of a software tool to enhance underwater images with well-known methods at the SoA. A benchmark of these well-known methods has been produced and some guidelines to evaluate the underwater image enhancement methods have been formulated. The effort of this part of the research has been to guide the community towards the definition of a more effective and objective methodology for the evaluation of underwater image enhancement methods. Another aspect of the research concerned the Underwater Navigation and Underwater AR (UWAR). A software for underwater tablets, namely Divy, has been designed and developed to support divers’ navigation and exploration. It enables the divers to access different features such as the visualization of a map of the underwater site that allows them to know their position within the submerged site, the possibility to acquire geo-localized data, the visualization of additional information about specific points of interest and the communication with the surface operators through an underwater messaging system. On this basis, the UWAR concept applied in Underwater Cultural Heritage sites has been designed and developed as well, consisting of an augmented visualization representing a hypothetical 3D reconstruction of the archaeological remains as they appeared in the past. The geo-localization is provided by an acoustic localization system, but this kind of technology suffers from a low update rate, and cannot be employed alone for the AR purpose. To improve the performance of the UWAR and provide the users with a smooth AR visualization, a hybrid technique that merges data from an acoustic localization system with data coming from a visual inertial-odometry framework has been conceived and developed to deliver positioning information with a higher update rate with respect to the acoustic system alone. In particular, given the low update rate of the acoustic system, a strategy has been implemented aimed to fill the gaps between two consecutive acoustic positioning data. User testing has been conducted to assess the effectiveness and potential of the developed UWAR technologies. Finally, an innovative approach to dive planning based on an original underwater pathfinding algorithm has been conceived. It computes the best 3D path to follow during the dive in order to maximise the number of Points of Interest (POIs) visited, while taking into account the safety limitations strictly related to scuba diving. This approach considers the morphology of the 3D space in which the dive takes place to compute the best path, taking into account the diving decompression limits and avoiding the obstacles through the analysis of a 3D map of the site.