Feasibility of Acoustically Determining the Thickness of Sea Ice

• Main Author: Bunney, Robert E.
• Other Authors: WASHINGTON UNIV SEATTLE APPLIED PHYSICS LAB
• Format: Text
• Language: English
• Published: 1974
• Subjects: Snow; Ice and Permafrost; Acoustic Detection and Detectors; Acoustics; *ACOUSTIC PROPERTIES; *SEA ICE; COMPUTER PROGRAMS; MEASUREMENT; THICKNESS; INTERFACES; SOUND TRANSMISSION; ACOUSTIC ATTENUATION; REFLECTIVITY; SONAR ECHOES; ACOUSTIC VELOCITY; SEA WATER; LOW FREQUENCY; ACOUSTIC REFLECTION; SOUNDING; SONAR PULSES; *PULSE ECHO TECHNIQUE; *ACOUSTIC SOUNDING; Ice; permafrost; Sea ice
• Online Access: http://www.dtic.mil/docs/citations/ADA118499; http://oai.dtic.mil/oai/oai?&verb=getRecord&metadataPrefix=html&identifier=ADA118499

The principal objective of this investigation was to experimentally determine the feasibility of using acoustic pulse echo techniques to measure the thickness of sea ice. Field tests performed on both winter and annual sea ice showed that a pulse echo technique is entirely feasible if: (1) adequate coupling between the sound source and the ice surface is obtained, and (2) either the source levels are kept sufficiently high or the frequency is kept low enough that the wavelength of the sound is large compared to the size of the sound-scattering centers in the ice. Our measurements of the compressional and shear wave velocities parallel to the axis of the ice indicate that such thickness measurements can be accurate to within 1.5%. The tests indicated that the acoustic impedance mismatch at the ice water interface is sufficient to allow the use of either the compressional or the shear wave. Before the shear wave could be used, however, an efficient method would have to be found for establishing a reliable bond between the ice and the acoustic source. We did not obtain sufficient data to verify reports in the literature that seasonal variations in both the compressional and shear wave velocities approach 20%.