5aUW6. Modal coupling in forward propagation through a layered dipping sediment with consolidation.

Session: Friday Morning, December 6

Time: 9:04

Author: Roger M. Oba
Location: Naval Res. Lab., Washington, DC 20375-5320


A parabolic equation with shear is used to compute the acoustic field in a shallow-water environment with a layered dipping sediment. Such sediments are typically formed by erosion of consolidated tectonically upturned layers. These are modeled in tilted sediment structure of a uniform vertical thickness over a range-independent hard sub-bottom. The water sound speed is range independent and depth dependent in a fixed depth environment. The PE propagated acoustic field is decomposed into local modes. In some instances the regularity of the layering permits a reasonable approximation by periodic layer spacing. Periodic layering gives significant structure to its modal coupling determined largely by the horizontal aspect of the layer spacing. Treating the interlayer spacing as a gamma-distributed random variable introduces phenomena not found in the periodic case. Even with very slight sediment tilt, transmission loss can be significantly different from the case with horizontal layering. The relative contribution of shear modulus compared to other parameters, especially density as it contributes to impedence mismatch, is explored.

ASA 132nd meeting - Hawaii, December 1996