Ambient noise measurements were made at seven different locations during the first four months of 1977. The measurement systems included: two types of towed arrays, a bottomed array, and systems with sensors distributed throughout the water column. The noise in the frequency regime dominated by shipping was found to be extremely high with a spectrum level of 92 dB//1 /spl mu/Pa at 50 Hz. These high levels were attributed to the high-density shipping. Horizontal directionality of the noise varied from site to site, ranging from highly directional to nearly nondirectional. The character of the directionality was highly dependent on the site position relative to shipping lanes. The noise showed very little dependence on depth.

Ambient noise measurements in the northwest Indian Ocean

: This report presents recommendations for future measurements and techniques for estimating the horizontal directionality of ocean ambient noise The recommendations are based upon (a) evaluations of present measurement data and techniques, (b) assessments of possible measurement-array configurations and techniques, and (c) the sensitivities of horizontal directionality measurements to vertical arrival structures

C. B. Burroughs

Papers

Horizontal Directionality of Ocean Ambient Noise.