Performance of a Passive Acoustic Linear Array in a Tidal Channel

Baseline ambient sound level assessment is important in quantifying anthropogenic noise contributions. Static acoustical sensing in high-flow conditions is complicated by pseudosound, or flow noise, caused by turbulent flow on the surface of a hydrophone. Signal processing methods are used to identify and suppress flow noise at low frequencies (
$< $
500 Hz) in data collected on a four-element horizontal hydrophone array in Minas Passage, a tidal channel in the Bay of Fundy, in October 2016. Spectral slope analysis is used to identify the frequencies at which the flow noise and ambient noise contributions to the recorded signal are equal, between 180 and 275 Hz for current speeds of 0.1 to 2.6 m/s, respectively. The maximum frequencies at which flow noise is observed, between 100 and 125 Hz over the same current speed range, are determined using analysis of the spatial coherence. The array's performance in the Minas Passage is quantified by an empirical relationship between flow speed and the spectral critical frequencies of the coherent output from the linear array. Coherent averaging (broadside beamforming) is demonstrated as a potential flow noise suppression technique, improving low-frequency passive acoustic monitoring in a high-energy tidal channel.