Underwater acoustic source signatures from recreation boats - Field measurement and guideline

The knowledge of the noise characteristics from recreational boats is scarce and there is little evidence to draw any conclusions on impact and recommend any measures. The first step to decrease this knowledge gap is to measure the underwater radiated noise (URN) from boats and calculate their source level. This study aims to develop a methodology for source level estimations of recreational boats and test it in field trials, where the URN from three boats are recorded. Parameters such as speed, measurement depth, direction, distance and transmission loss estimations are varied, aiming to study their effect on the calculated source level. One field campaign was carried out in 2019 and one in 2020. By combining the boats' GPS position and a hydrophone system's sound data, successful measurements of the boats' URN and their source levels was estimated. The acoustic signatures of all boats showed clear tones, stemming from the engines' and propellers' rotational frequencies. The estimated source level error was about ±3 dB. Finally, a measurement guideline was developed for the estimation of recreational boats' acoustic signature that can be used for comparison with published scientific studies, environmental impact studies and as input to source models.