The Effect of Sediment Rigidity on Bottom Reflection Loss.
Abstract
The plane wave reflection coefficient R of a horizontally stratified ocean bottom is studied for typical deep sea sediment types in order to determine the importance of sediment rigidity (shear wave propagation) on bottom reflection loss, RL=-20 log(absolute value of R) dB. The emphasis is on, but not restricted to, low grazing angles (0 to 45 deg) and low frequencies (10 to 200 Hz). R is studied using a computational model accurate for frequencies above 10 Hz which treats a single inhomogeneous (solid) sediment layer overlying a homogeneous (solid) substrate. An examination of the reflection and transmission coefficients at the water-sediment and sediment-substrate interfaces, by means of an expansion in the ratio of sediment shear speed to the sound speed in water, reveals the mechanism for exciting sediment shear waves and provides an understanding of the empirical separation into 'thick' and 'thin' sediments. At the water-sediment interface sediment shear waves are not efficiently excited and the sediment can be treated, in most cases, as a fluid. The dominant mechanism for exciting sediment shear waves is compressional wave conversion at the sedimen t-substrate interface. At a given grazing angle in a thick sediment the compressional wave will have a turning point well above the sediment-substrate. Compressional wave amplitude at the interface will be small.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 19, 1979
- Accession Number
- ADA079661
Entities
People
- Paul J. Vidmar
Organizations
- University of Texas at Austin