Accession Number : ADA324900

Title :   Finite Difference Modeling of Bottom Reverberation.

Descriptive Note : Final rept. 1 Sep 93-28 Feb 97,

Corporate Author : WOODS HOLE OCEANOGRAPHIC INSTITUTION MA

Personal Author(s) : Stephen, Ralph A.

PDF Url : ADA324900

Report Date : 07 MAY 1997

Pagination or Media Count : 3

Abstract : Finite difference modeling was used to compare scattering from volume and interface heterogeneities at the seafloor. Two-dimensional and three-dimensional models for flat seafloors with sub-bottom heterogeneities, single facets, and statistically rough seafloors were compared. Significant secondary and tertiary scattering from rough, hard bottoms representative of basaltic seafloors was observed. The results indicate that two-dimensional techniques may be appropriate for modeling sub-bottom volume heterogeneities with velocity contrasts less than 10%. The discrepancy between twodimensional and three-dimensional models is partly attributed to sub- surface conversion to horizontally polarized shear waves on 3-D models for both volume and interface heterogeneities. The results of the 3-D modeling were used, in part, to explain observations of ambient noise below the seafloor. Analysis of the ARSRP acoustic backscatter data from Site A was completed. The correlation between backscattered signals from 'inside come?' and 'outside come?' crust and the observed hydrosweep bathymetry was studied. It was concluded that the seafloor dip, on the scale of a few hundreds of meters, influences but does not determine scattering strength. Other characteristics of steeply dipping areas, such as subsurface properties or smaller scale surface features, strongly affect backscattered signals.

Descriptors :   *FINITE DIFFERENCE THEORY, *ACOUSTIC SCATTERING, *ACOUSTIC DATA, SHEAR PROPERTIES, CONVERSION, MATHEMATICAL MODELS, VOLUME, SCATTERING, POLARIZATION, MODELS, INTERFACES, BACKSCATTERING, BASALT, SURFACES, THREE DIMENSIONAL, BATHYMETRY, SCALE, SIGNALS, STRENGTH(GENERAL), HETEROGENEITY, HORIZONTAL ORIENTATION, REVERBERATION, AMBIENT NOISE, ROUGHNESS, BOTTOM, SUBSURFACE, OCEAN BOTTOM, ELASTIC WAVES.

Subject Categories : Theoretical Mathematics
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE