Master thesis : Design of a System to Investigate Underwater Radiated Noise of Small Craft

Abstract

Underwater Radiated Noise started to be recognized as a threat to the marine ecosystem balance about 50 years ago. Since then, regulations and evaluations of the acoustic signature of big-sized ships have become a common practice. Nowadays, the detection, localization, tracking, and classification of this kind of ship are accurately estimated by radar or AIS. However, in recent years the number of small and mid-sized ships has been increasing rapidly along with human recreational activities in coastal zones, and now is required a better understanding of their environmental impact. Small craft are challenging to detect because of lack of AIS and they have weak acoustic signatures for the most common monitoring systems. Moreover, information published in the literature about the acoustics of this kind of ship is limited, even though they can be widely diverse. This work describes the methodology to design a system to investigate underwater-radiated noise of small craft using only acoustic means. At first, a Direction of Arrival (DOA) model considering two, three and four receivers was formulated and validated. Second, a 4-hydrophones array measurement system was designed, assembled and tested in the bay of Kiel, recording sample data from a motor sailing boat and other vessels passing nearby. Then, the data was processed and evaluated with the DOA model to estimate the bearing location of the recorded sources. Finally, the results were compared with the GPS data from the ships. The system shall then be able to detect the presence of several small craft to later allow entering this information into soundscape calculations.