Stevens Passive Acoustic Detection System (SPADES-2) and its prospective application for windfarm underwater noise assessment

Stevens Institute of Technology has been conducting development and field tests of various underwater passive acoustic systems for several years. Several such systems provided localization of boats and divers. The new version of SPADES has a tethered bottom-mounted circular 2.2-m underwater acoustic array with eight hydrophones. Since the cost of underwater acoustic sensing hardware limits the ubiquitous, the cost of the array was significantly reduced compared with the previous version of SPADES due to manufacturing the hydrophones in-house and utilizing a lightweight tether marketed for remotely operated vehicles (ROV). The tether can provide power and communication up to 1 km away and power to the data acquisition. The software has been developed for real-time direction-finding using Steered Power Response Phase Transform (SRP-PHAT) method, combined with the region-zeroing (RZ) approach to multi-source separation. The array was tested for seven months in the shallow and busy waters of the Hudson River tracking small boat activity. The system's reliability and long tether make it attractive for long-term observation of underwater noise such as monitoring wind farm noise, marine mammals, and shipping traffic. Direction-finding can help identify noise unrelated to wind farms.