Vertical line array tilt revealed through snapping shrimp noise

Abstract

The shallow-water acoustic variability experiment (SAVEX15), conducted in the East China Sea, unexpectedly recorded a great deal of snapping shrimp noise on a 16-element (56-m length) vertical line array deployed in 100-m water depths. These impulsive events can be used to find the tilt of the moored array which was caused by the strong ocean currents in the area. In this environment, the recorded snaps of bottom-dwelling shrimp within a radius of more than 500 m were largely separated from one another in time, and coherent time domain beamforming was successful in localizing snaps in time and range. The sparse and impulse nature of the snaps allowed for a simple normalization and gave tens of snap detections per second after a threshold detector. The results from the automated detector showed it was necessary to search with the beamformer over a three-dimensional space for reliable performance: (1) arrival time, (2) source range, and (3) array tilt. The results of the beamformer search in array tilt space are consistent with independent acoustic tilt measurements of the same array, showing that snapping shrimp noise in this region can provide valuable inference for the acoustic environment.