ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

1aAO2. Predictions of the acoustic response of free-methane bubbles in muddy sediments.

Anthony P. Lyons

Michael E. Duncan

Dept. of Oceanogr., Texas A&M Univ., College Station, TX 77843-3146

James A. Hawkins, Jr.

Naval Res. Lab., Stennis Space Center, MS 39529-5004

Aubrey L. Anderson

Texas A&M Univ., College Station, TX 77843-3146

The response of the sediments of Eckernfoerde Bay, Germany to acoustic remote sensing has been attributed to gas features found within the sediment. The existence of features as small as 0.5 mm equivalent spherical radius has been confirmed by x-ray computed tomography of cores taken and scanned under in situ pressures. The interaction of an acoustic pulse from the Acoustic Sediment Classification System (ASCS) with this type of gassy sediment was modeled. The bubble scattering response included the effects of shear modulus and nonspherical bubbles. Model predictions made using the observed gas feature distribution and normal incidence ASCS data agree and show extended returns (greater than a pulse length) from the seafloor bubble layers as well as high attenuation within the bubble layers. These results show that the acoustic returns from the gas bubble layers are probably due to scattering and that differences in level of return can be attributed to random variations in the distributions of scatterers.