A useful theoretical measure of acoustic interaction with the seafloor is the plane wave reflection coefficient (J?), which is commonly expressed as bottom loss (—20log ᴵ R ᴵ). Predictions indicate that when the seafloor is modeled as a refracting layer over a basement half-space, the bottom loss is proportional to frequency. Bottom loss measurements in the 50-1600-Hz b, however, frequently show a loss that is inversely proportional to frequency. For example, roughly one-third of a set of measured bottom loss data in the North Atlantic exhibit this anomalous frequency dependence. It is concluded that the anomalous frequency dependence is due to sedimentary fine-scale layering arising from turbidity currents. The evidence presented consists of (1) a high correlation between the anomalous bottom loss stations and the bounds of the abyssal plains and (2) favorable predictions between a model accounting for the layering and the measured data. The study area was the western North Atlantic including the Sohm, Hatteras, and Nares abyssal plains. A simple, approximate stochastic model of reflection from a quasiperiodic sedimentary sequence was developed that appears to account for the dominant physical mechanisms important in the reflection process in this type of physiographic province.
All Science Journal Classification (ASJC) codes
- Acoustics and Ultrasonics
- Arts and Humanities (miscellaneous)