ASA 127th Meeting M.I.T. 1994 June 6-10

1pUW1. Vertical noise versus wind speed.

Joan C. Lange

Stephen K. Mitchell

Scott J. Levinson

Appl. Res. Labs., Univ. of Texas at Austin, Austin, TX 78713

The outpost sunrise exercise was conducted at a deep, high bottom loss area in the Pacific Ocean. Vertical 24-element arrays, nested for 75 and 150 Hz, were moored at the seabottom and at critical depth. The exercise was conducted during the fall, when high wind speeds are likely; wind speed (w) was recorded from a nearby buoy. For w(greater than or equal to)4.5 m/s, omnidirectional noise depended on receiver depth and frequency band. At 300 Hz, ambient noise recorded below the critical depth was well correlated with wind speed, but at lower frequencies, this was not so. Correlation of beam noise level [BNL((phi))] for w(greater than or equal to)4.5 m/s depended on vertical angle (phi). Horizontally ((phi)=0(degrees)), the field was dominated by distant noise. BNL((phi)) for (phi)(less than or equal to)15(degrees) closely tracked w. BNL((phi)) was estimated at 65 and 130 Hz. BNL(90(degrees)) increased from 55 to 70 dB//(mu)Pa[sup 2] Hz-sr as w increased from 4.5 to 11 m/s. Theoretical BNL((phi)) with source directionalities of a dipole, plane of monopoles, and volume of monopole planes are compared with data. A source modeled as a of a plane of monopoles between (lambda)/5 and (lambda)/3 depth best fist the data. [Work supported by the Office of Naval Research.]