Seismic Scattering of Low-Grazing-Angle Acoustic Waves Incident on the Seafloor
Abstract
The goal of this thesis is to develop a methodology to interpret sound scattered from the seafloor in terms of seafloor structure and subseafloor geological properties. Specifically, this work has been directed towards the interpretation of matched-filtered, beamformed monostatic acoustic reverberation data acquired on the west flank of the Mid-Atlantic Ridge when the seafloor is insonified by a band-limited, low-grazing-angle acoustic pulse. Analysis of monostatic reverberation data acquired at Site A on the ARSRP 1993 Acoustics Cruise suggests that the scattered signals cannot be quantitatively explained in terms of large-scale slope alone, even though a strong correspondence between high intensity backscatter and seafloor ridges is observed. Numerical modeling using a finite-difference solution to the elastic wave equation shows that large-scale seafloor slope and subseafloor average velocity influence the backscattered intensity levels but that the source of scattering is wavelength-scale heterogeneity. Modeling results show that scattering from rough, basaltic bottoms is dominated by interface scattering. Subseafloor volume heterogeneity is shown to be capable of producing scattered signals comparable to rough seafloor scattering when the bottom is smooth and/or has a low velocity. An effective Rayleigh roughness parameter is defined that incorporates all seafloor structure parameters, including large-scale slope, the correlation length and rms height of wavelength-scale structure, and the acoustic beam grazing-angle. This leads to an interpretation scheme for backscatter intensity in terms of seafloor roughness.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 1998
- Accession Number
- ADA363628
Entities
People
- Robert J. Greaves
Organizations
- Massachusetts Institute of Technology