Operational Research of AIS AtoNs in Inland Waterways: A Case Study of a Selected Stretch on the Danube

Abstract

This study investigates the deployment and operational performance of AIS Aids to Navigation (AtoNs) on the Danube River, focusing on a selected 9-kilometer stretch in Slovakia. The research is aimed at assessing the radio visibility, energy consumption, impact on VHF Data Link (VDL) load, and positional accuracy of the deployed buoys, providing insights for future implementations on inland waterways. Radio visibility has remained stable, with a success rate of over 90% for receiving transmitted AIS messages during uninterrupted operational periods. However, high water levels have disrupted operations by sweeping buoys away, necessitating re-deployment. Energy consumption analysis has revealed that AtoN Type 1, which operates without sensors, has maintained a stable battery voltage above the critical level (12.4 V) throughout the test period, even during cloudy conditions. For AtoN Type 3, the battery has also remained stable without sensors. However, when operating in repeater mode or with sensors, the battery levels have dropped below the critical point during extended periods of reduced sunlight, leading to communication failures and necessitating external charging. The study has also evaluated the VDL load impact, finding it minimal, even when the buoys operating in repeater mode. Specifically, AtoNs without sensors has been used only 0.6% of the available VDL slots, indicating a negligible effect on the overall system. Positional accuracy has been was assessed by analysing "off-position" alerts. Initial settings have shown frequent off-position reports, especially during high water conditions. Adjusting the radius to 150 meters has significantly reduced these alerts, achieving near-perfect position retention during the final testing phase, except for occasional deviations likely due to environmental factors. While AIS AtoNs shows promise for enhancing inland waterway navigation, challenges such as anchoring stability during high water, energy management, and precise positioning require further refinement. These findings are critical for guiding the broader deployment of AIS AtoNs in inland waterways.