Visual acquisition system for georeferenced monitoring and reconstruction of the sea bottom using audio for data synchronisation

This work describes a Smart Dive Scooter (SDS) to be used as a support tool for monitoring application of different marine species. Professional divers of Environmental Protection Agencies are periodically involved in monitoring activities. Ligurian Regional Agency for the Environmental Protection (ARPAL) and the University of Pisa (UNIPI) are collaborating towards the integration of classical methodologies with ICT tools to support the work of divers in terms of safety, cost effectiveness and time effectiveness. The SDS is the first step in this direction. It is a classical Dive Scooter, used for rapid movements underwater, that is integrated with sensors for environment monitoring (a set of cameras) and for data georeferencing (acoustic localisation system). The SDS will be used by ARPAL divers to quickly acquire images of the bottom of a target area. Processing of optical and positioning data will allow to build a virtual model on which perform all the analysis and measurement activities. This approach results in limiting the time underwater for operators increasing the area mapper per each dive. The paper focuses on the technique used for the synchronization of optical data among the various cameras and of them with the acoustic position measurements. This goal is obtained exploiting the audio tracks acquired by the cameras avoiding the necessity of bulky and energy expensive dedicated computers. Results of the validation based on experimental data collected at sea are reported.