Sound Speed, Reflectivity, and Absorption Measurements in Arctic Ice in 1988
Abstract
Acoustic measurements at 20-300 kHz were made in the Arctic in Spring 1988 to study sound speed and absorption within the ice canopy and the reflectivity of the water-ice interface. An average sound speed of 3669 + or - 29 m/s was found for first-year ice, with evidence that the speed varied from 3800 m/s in solid ice to 2000 m/s in the so called skeletal layer at the lower boundary. The absorption, alpha, for vertical transmissions was found to be three times as high as that given in the literature for horizontal transmissions; the recommended frequency and temperature dependence is alpha = 0.19f(-6/T)(to the 2/3 power) for temperatures between T = -2 and T = -20 C. The reflectivity of the lower surface of the ice decreased from 0.2 at 20 KHz to 0. 04 at 200 kHz for sound impinging at normal incidence. A simple model that treats the echoes as the sum of reflections from two surfaces, one at the interface between the water and the skeletal layer and one at the transition from the porous skeletal layer to solid ice, matches the experimental results with reasonable accuracy.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 1991
- Accession Number
- ADA246293
Entities
People
- G. R. Garrison
- R. E. Francois
- R. P. Stein
- T. Wen
- W. J. Felton
Organizations
- University of Washington