Augmented reality can be deployed in various application domains, such as enhancing human vision, manufacturing, medicine, military, entertainment, and archeology. One of the least explored areas is the underwater environment. The main benefit of augmented reality in these environments is that it can help divers navigate to points of interest or present interesting information about archaeological and touristic sites (e.g., ruins of buildings, shipwrecks). However, the harsh sea environment affects computer vision algorithms and complicates the detection of objects, which is essential for augmented reality. This paper presents a new algorithm for the detection of fiducial markers that is tailored to underwater environments. It also proposes a method that generates synthetic images with such markers in these environments. This new detector is compared with existing solutions using synthetic images and images taken in the real world, showing that it performs better than other detectors: it finds more markers than faster algorithms and runs faster than robust algorithms that detect the same amount of markers.

Underwater cultural heritage sites represent an attractive and exciting experience for diving tourists, even if often it is complicated for them to understand the significance and value of the remains that are usually strongly damaged and covered by the marine organisms. Thanks to the recent advancements in technologies that overcome these problems, augmented reality is nowadays possible even in such harsh conditions, opening new possibilities for enhancing the diver's experience. However, no user study has formally evaluated the usefulness and usability of augmented reality in open sea underwater environments. This paper presents two novel solutions for underwater augmented reality: a compact marker-based system for small areas, and a complex acoustic system for large areas. Both of them were deployed at an underwater cultural heritage site and evaluated by ten divers in experiments analyzing their perception and remembrance, interests, and user experience. For comparison, the same study was also performed with non-divers assessing the marker-based system on land. Results show that both systems allow divers to encounter new and exciting moments and provide valuable insights for underwater augmented reality applications.