Wind-generated ambient noise in the deep ocean trenches

Under the influence of the wind, breaking waves create bubbles, which oscillate as monopoles thus acting as efficient sources of sound. In the deep ocean trenches, bottom reflections are often negligible and the bubble-generated ambient noise is primarily downward traveling. The Deep Sound instrument platform is designed to record the noise on pairs of hydrophones, aligned vertically and horizontally, to depths as great as 11 000 m. Deep Sound consists of a Vitrovex glass sphere, three recovery antennas, a high-performance data acquisition system, inertial navigation, and a CTD plus sound speed sensor, with power provided by lithium-ion batteries. It descends under gravity, and releases a drop weight at depth, at which point it returns to the surface under buoyancy, collecting sound speed and acoustic data on the descent and ascent. Deep Sound has been deployed in the Challenger Deep in the Mariana Trench, the Tonga Trench, the Sirena Deep, and the Philippine Sea. One of the conclusions from the data is that the noise field in the deep trenches conforms to the simple Cron and Sherman theoretical model provided that the local sound speed is used in the computation of the spatial coherence of the noise. [Research supported by ONR.]