Automatic detection of boats in underwater recordings

Abstract

The research addresses a growing environmental challenge in Swedish coastal waters, where increasing recreational boat traffic poses risks to marine ecosystems through underwater noise pollution [1]. While commercial vessels can be tracked through AIS transponders, the vast majority of recreational boats operate without monitoring systems [2], leaving a significant gap in our understanding of their environmental impact. To address this challenge, an automated detection system using underwater acoustic recordings was developed to identify and quantify recreational boat presence in coastal waters. Building on established signal processing techniques, a detection system based on the short-time-average/long-time-average (STA/LTA) algorithm was implemented [3]. The focus is on optimizing three key components: bandpass filtering parameters, window functions, and detection thresholds. During fieldwork in August 2024, continuous underwater recordings along the Swedish coast were collected using SoundTrap and RTsys hydrophones. To validate the system’s performance, Reciever Operating Characteristic (ROC) curves were used [4] to fine-tune the detection parameters for optimal sensitivity while minimizing false positives. Through systematic testing, an STA of 3 minutes and an LTA with the same length as the recording were found to yield the best performance. The frequency band of 100 Hz to 4000 Hz showed the highest effectiveness in detecting vessel noise. Threshold optimization revealed that values below 0.5 minimize missed detections, while values above 0.8 reduce false positives, establishing an optimal operating range of 0.5 to 0.8. These values were obtained from recordings containing numerous boat passages. They may vary for recordings with fewer passages. The resulting energy detector offers a practical and adaptive solution for monitoring recreational boat activity. These findings enhance the ability to quantify anthropogenic noise in marine environments and provide a foundation for informed environmental protection efforts.