Abstract
This paper presents the development of a low-energy passive acoustic vessel detector to work as part of a wireless underwater monitoring network. The vessel detection method is based on a low-energy implementation of Detection of Envelope Modulation On Noise (DEMON). Vessels produce a broad spectrum modulated noise during propeller cavitation, which the DEMON method aims to extract for the purposes of automated detection. The vessel detector design has different approaches with mixtures of analogue and digital processing, as well as continuous and duty-cycled sampling/processing. The detector re-purposes an existing acoustic modem platform to achieve a low-cost and long-deployment wireless sensor network. This integrated communication platform enables the detector to switch between detection/communication mode seamlessly within software. The vessel detector was deployed at depth for a total of 84 days in the North Sea, providing a large data set, which the results are based on. Open sea field trial results have shown detection of single and multiple vessels with a 94% corroboration rate with local Automatic Identification System (AIS) data. Results showed that additional information about the detected vessel such as the number of propeller blades can be extracted solely based on the detection data. The attention to energy efficiency led to an average power consumption of 11.4 mW, enabling long term deployments of up to 6 months using only four alkaline C cells. Additional battery packs and a modified enclosure could enable a longer deployment duration. As the detector was still deployed during the first UK lockdown, the impact of COVID-19 on North Sea fishing activity was captured. Future work includes deploying this technology en masse to operate as part of a network. This could afford the possibility of adding vessel tracking to the abilities of the vessel detection technology when deployed as a network of sensor nodes.
Highlights
Introduction published maps and institutional affilOur oceans cover more than 70% of the world’s surface and for island nations such as the United Kingdom (UK), this can result in a large amount of coastline being vulnerable if not effectively monitored [1]
The acoustic modem is band limited to the propeller cavitation band of interest and resonant frequency of the transducer, which will be used in the remaining vessel detector design
A rigid hulled inflatable boats (RHIB) owned by Newcastle University was instructed to make several passes near to the vessel detector within the Port of Blyth estuary
Summary
Our oceans cover more than 70% of the world’s surface and for island nations such as the United Kingdom (UK), this can result in a large amount of coastline being vulnerable if not effectively monitored [1]. The English channel spans approximately 75,000 km and weather conditions can be extreme, especially during the winter months [9]. To monitor such a large area in all conditions using sea- and air-based vehicles would be challenging, incredibly labour intensive, and could carry a sizeable cost. A low-cost alternative to detect surface vessels could help to address some of the examples illustrated for monitoring ocean activity
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