UOTag: An All-Angle Passive Optical Tag for Underwater Environment

Underwater operations require divers to access location-specific information, such as inspection protocols and safety guidelines. However, existing technologies face significant limitations: acoustic systems rely on expensive and bulky transceivers, RF communication is limited to centimeter-scale range, and laser systems require precise alignment. In this paper, we present UOTag, a passive, all-angle optical tag system leveraging commercial off-the-shelf (COTS) smartphones as receivers for underwater information retrieval. Traditional optical tags like QR codes provide high information capacity but perform poorly underwater due to narrow viewing angles and a limited range of just 3-6 meters. UOTag adopts the QR code concept for underwater information delivery and leverages a rhombic dodecahedron structure to enable 360° three-dimensional viewing angles, allowing tag access from any direction and eliminating alignment constraints. The system incorporates an underwater-optimized encoding-decoding framework and replaces black-and-white QR codes with a blue-yellow color scheme, effectively extending operational range underwater. Real-world experiments in a pool and at sea show working distances of 11.8 meters and 7.2 meters, respectively, using a compact tag with an edge length of just 15 cm. The system operates with a latency of just 113 ms and costs $8.50 per tag, enabling practical deployment as a convenient information source for divers.