Accession Number:

ADA196631

Title:

Estimation of Ice Surface Scattering and Acoustic Attenuation in Arctic Sediments from Long-Range Propagation Data

Descriptive Note:

Corporate Author:

MASSACHUSETTS INST OF TECH CAMBRIDGE

Personal Author(s):

Report Date:

1984-01-01

Pagination or Media Count:

14.0

Abstract:

A single explosive shot at a range of 341.3 km in the Pole Abyssal Plain of the Arctic Ocean is used to assess the components of propagation loss for this region. The acoustic energy propagated between a satellite ice camp and the Fram II ice station in a water column of nearly uniform depth. Much of the observed energy interacted with the upper 200 meters of sediments along a path which was nearly parallel to the Arctic Mid-Ocean Ridge. In addition, the upward refracting sound channel of the Arctic Ocean also caused the observed energy to interact extensively with the ice canopy, which was contiguous over the entire path. The deterministic lateral homogeneity of the bathymetry and sediments, and the statistical lateral homogeneity of the ice canopy in this region allow us to attempt to separate the effects of geometrical spreading, ice surface scattering, and effective sediment compressional wave attenuation. The primary data for this work are observations of the signal from a 25.8 kg explosive charge received on a 24 channel two-dimensional hydrophone array with a 1 km aperture. The data are inadequate to resolve attenuation at depth, but provide an estimate for frequency independent Q of 200 to 300 for the upper 200 meters of the sediments and a dependency of surface scattering on frequency over the 5- 50 Hz band. It is shown that partially coherent summation of the surface multipaths is required to predict the observations.

Subject Categories:

  • Snow, Ice and Permafrost
  • Acoustics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE