The response of the sediments of Eckernfoerde Bay, Germany to acoustic remote sensing previously has been attributed qualitatively to gas features which were postulated to exist in situ within the sediment. The existence of features as small as 0.5-mm equivalent spherical radius has now been confirmed by x-ray computed tomography of cores taken and scanned at in situ pressures. The interaction of an acoustic pulse from the acoustic sediment classification system (ASCS) with this type of gassy sediment was modeled and the results are presented here. The bubble scattering response model includes both the effects of nonspherical bubbles and of sediment resistance to shear deformation (as expressed by the dynamic shear modulus). Model predictions made using the observed gas bubble distribution agree with normal incidence ASCS data, exhibiting extended returns (i.e., greater than the source pulse length) from the seafloor bubble layers as well as high attenuation within the bubble layers. Spectrograms of ASCS and modeled return pulses were also similar. These results suggest that the acoustic return characteristics of the near surface sediments of Eckernfoerde Bay are dominated by scattering from a distribution of gas bubbles with depth.
