Jiang, YuehanYuehanJiangRenner, Bernd-ChristianBernd-ChristianRenner2026-01-302026-01-302025-12-04IEEE International Symposium on Multi-Robot and Multi-Agent Systems, MRS 2025https://hdl.handle.net/11420/61213We present an online underwater localization method that enables passive vehicles to localize themselves by overhearing two-way ranging (TWR) communication between an active vehicle and multiple acoustic anchors. Swarm simulations confirm the scalability of the system and show faster position updates, as well as improved accuracy compared to the active benchmark. A field experiment in a shallow water canal using the low-cost BlueROV2 underwater vehicle and ahoi modems has demonstrated the real-world applicability of the system, achieving an RMSE of approximately 0.82m.enTechnology::600: TechnologyConference Paper10.1109/mrs66243.2025.11357275Conference Paper