  The Mediterranean Sea has a vast maritime heritage which exploitation is made
difficult because of the many limitations imposed by the submerged environment.
Archaeological diving tours, in fact, suffer from the impossibility to provide
underwater an exhaustive explanation of the submerged remains. Furthermore, low
visibility conditions, due to water turbidity and biological colonization,
sometimes make very confusing for tourists to find their way around in the
underwater archaeological site. To this end, the paper investigates the
feasibility and potentials of the underwater Augmented Reality (UWAR)
technologies developed in the iMARECulture project for improving the experience
of the divers that visit the Underwater Archaeological Park of Baiae (Naples).
In particular, the paper presents two UWAR technologies that adopt hybrid
tracking techniques to perform an augmented visualization of the actual
conditions and of a hypothetical 3D reconstruction of the archaeological
remains as appeared in the past. The first one integrates a marker-based
tracking with inertial sensors, while the second one adopts a markerless
approach that integrates acoustic localization and visual-inertial odometry.
The experimentations show that the proposed UWAR technologies could contribute
to have a better comprehension of the underwater site and its archaeological
remains.
