Acoustic Reflections from Cylindrical Blocks of Arctic Ice, 1986

• Main Authors: Garrison, G. R., Francois, R. E., Wen, T., Stein, R. P.
• Other Authors: WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
• Format: Text
• Language: English
• Published: 1988
• Subjects: Snow; Ice and Permafrost; Acoustic Detection and Detectors; Acoustics; *ACOUSTIC MEASUREMENT; *SEA ICE; *ICE; *ACOUSTIC REFLECTION; PHYSICAL PROPERTIES; WATER; SOLIDS; REDUCTION; SURFACES; FREEZING; PULSES; CYLINDRICAL BODIES; RESPONSE; RECEIVERS; PATTERNS; CANOPIES; ACOUSTIC SIGNALS; TRANSITIONS; UNDERWATER ACOUSTICS; BOTTOM; TARGET STRENGTH; ARCTIC REGIONS; UNDERWATER TARGETS; SKELETON; SOUND GENERATORS; LAYERS; CORES; UNDERICE; FREQUENCY; ANGLES; ACOUSTIC MEASUREMENT; SEA ICE; ICE KEELS; PE62435N; Arctic; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA205074; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA205074

Measurements of acoustic reflections from cylindrical blocks of Arctic ice were conducted in Spring 1986. Blocks with diameters of 40, 84, and 109 cm were individually cored out and depressed below the surface. Acoustic pulses were transmitted from below, and thus the returns from the depressed block at shorter range were separable from the reflections off the underside of the ice canopy. The sound source/receiver was moved horizontally beneath the block to measure the angular response pattern. The skeletal layer formed at the bottom of the ice during freezing appeared to reduce the reflection at normal incidence below that expected from the bulk physical properties of the ice; this reduction increased greatly with frequency in the measurement range, 20-80 kHz. The reflective properties are compared with the observed structure of the skeletal layer to understand the nature of the reflection. As used here, the term 'skeletal layer' refers to the transition zone between solid ice and water at the lower surface of sea ice. In spring 1986 the skeletal layer was 10-15 cm thick.