Passive diver detection in warm waters

Passive diver detection relies on the detection of sounds emitted by underwater breathing apparatus. It is limited by the ambient noise. Passive detection and localization of scuba divers in a port environment up to 400 m has been reported. The applicability of these methods to warm waters has not been demonstrated yet. Indeed, warm waters are noisy waters whose background noise is usually dominated by the noise produced by the marine life, in particular by snapping shrimps that generate very loud transients. In this study, we report the first investigation of the detectability of scuba divers in warm waters using passive acoustics. The study was performed using data collected using the ROMANIS system. ROMANIS is a 2D array of 1.3 m meter diameter equipped with 508 sensors and developed at the National University of Singapore for ambient noise imaging. The data analysed were collected in April 2010 while scuba divers were deploying a target for imaging at 70 m from the array. The data analysed presents significant level of snapping shrimp noise (more than 200 snaps per second). It was analysed using beamforming. The large number of sensors on the array allows for processing of the data using a subset of sensors, thereby enabling to study the influence of the number of sensors. The beamformed data enabled detection of the scuba diver’s inhalations and to determine their azimuth and elevation. The study indicates that passive diver detection is applicable in warm waters dominated by snapping shrimp noise