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

3pUW3. Ambient noise and reverberation in the Littoral Region west of Mallorca.

J. A. Shooter

H. J. Huang

C. L. Hackert

J. A. TenCate

T. G. Muir

Appl. Res. Labs., University of Texas at Austin, Austin, TX 78713-8029

A. Kristensen

A. Caiti

E. Michelozzi

M. Max

SACLANT Undersea Res. Ctr., 19026 LaSpezia, Italy

Experiments were carried out in the area west of Mallorca, Balearic Islands where the seafloor is a relatively flat, thin (~1 m), calcareous sand sediment atop a hard limestone bottom some 100 m below the sea surface. A linear, uniformly spaced array of 24 hydrophones with element separations of 2 m was deployed. Reverberation measurements were made with wideband (SUS) and narrow-band sources with the array deployed vertically and horizontally on the seafloor. The measurements show the area to be quite unique, due to the hard, flat, high velocity bottom. It is highly reverberant with unusually low ambient noise. Transmission loss measurements were made at several depths and have been analyzed with computations using OASES (SAFARI). For this area, the transmission loss and scattering strength are strongly frequency dependent. Both show a relatively high-frequency minimum in the 500- to 800-Hz band. Other unique features of this area are presented. [Work supported by Advanced Research Projects Agency, Maritime Systems Technology Office.]