FROG: A PORTABLE UNDERWATER MOBILE MAPPING SYSTEM

Abstract. Browsing the scientific and professional literature it appears that the concept of mobile mapping underwater is not as common as in ‘terrestrial’ applications. Nevertheless, exploring and mapping the ocean’s depths is a priority challenge for humankind, today more than ever. Radio waves, such as the GNSS or UWB signal, have a very limited transmission underwater, resulting in the absence of an underwater global positioning system. Consequently, the main sounding methods (i.e., depth measuring systems) are based on the fusion of inertial and acoustic sensors, which allow for systematic mapping of vast seafloor areas. However, photogrammetric surveying methods are preferred when high resolution and reliable colour information are essential aspects in the project economy. This class of approaches include visual odometry and visual SLAM (vSLAM), which represent a valid tool for navigation and positioning in GNSS-denied environments, such as underwater. In this paper, we present a portable underwater mobile mapping system, named FROG, which implements a vSLAM based solution to guide the survey according to photogrammetric principles. FROG is built upon the Guided Photogrammetry - GuPho concept and, thanks to its modular design, can be used by a diver or installed on a micro ROV and controlled remotely from a support vessel. In the paper, FROG characteristics will be detailed, and its potentialities demonstrated in real case applications at sea and in lakes.