Deep ocean noise measurements in the Philippine Sea.

Abstract

In the spring of 2009, a newly developed distributed vertical line array (DVLA) receiver made up of two, 1000‐m‐long subarrays with 30 hydrophones each was deployed for approximately 1 month in the northern Philippine Sea. One subarray spanned the sound‐channel axis, and the second subarray spanned the surface conjugate depth (about 4200 m). Twenty of the 30 hydrophones in the deep subarray were spaced 5 m apart (half‐lambda at 150 Hz), allowing the vertical directionality of the ambient noise below the surface conjugate depth to be determined. The minimum omnidirectional ambient noise levels decreased significantly below the surface conjugate depth at frequencies from 50 to 500 Hz, similar to behavior previously observed in the central North Pacific Ocean. The minimum noise levels presumably correspond to times when wind speeds are low and surface conditions are calm so that there is little locally generated, low‐frequency noise.