Motivation

Oceans and rivers have significant economic and ecological importance, which drives increasing interest in observing and understanding underwater environments. Many applications—including ropeless fishing, marine ecosystem monitoring, and tracking of equipment or divers—require reliable object detection and localization.
A particularly challenging example is river bedload tracing, which is used to study sediment transport processes in waterways.  Therefore, tracers integrated into artificial stones mimick real sediment particles sized down to 4 cm. They are deployed to the riverbed in large numbers and tracked over multi-year periods. As a result, tracers must be tiny, power-efficient, and low-cost, as they are typically not recovered.

Goals and Contributions

This project aims to enable thumb-sized passive acoustic tracers that last for years on a battery and cost only tens of Euros. To achieve this goal, our institute takes a holistic approach researching minimalistic Tracer hardware designs, optimal (wideband) waveforms, and robust detection and localization algorithms to make the most out of the limited energy budget of the tracers.

So far, our tracers

• achieved a runtime of over a year on a coin-cell battery while transmitting a beacon every 15s,

• could be detected over more than 400m distance in quiet waters,

• cost about 15€ per tracer (hardware only), including the transducer, and

• could be localized with below 10m accuracy.

Further research will aim at finding effective strategies to mitigate the destructive effects in realistic scenarios: Shallow-water areas exhibit strong multi-path propagation, complicating the accurate localization, and flow noise induced by the water flow around the hydrophones, especially relevant in rivers, introduces additional noise, reducing the detection distances.