Measurements of sound speed in two types of ice with different microstructure

Abstract

Measurements of sound speed were made on laboratory-grown ice samples serving as proxies for two types of sea ice with different microstructure. The first one, congelation ice, has relatively homogeneous structure typical for first-year sea ice. The second one, granular ice, with a more heterogeneous microstructure, was prepared as a proxy for retextured multi-year sea ice. Both samples had approximately equal bulk salinity (12 ppt) to isolate effects of different microstructure. Sound speed was estimated by measuring time of flight of 400 kHz pulses and was found in congelation ice to be about 10% higher than in granular ice. Error bounds were estimated to be within 1% based on same measurements made for plastic material with known sound speed. Therefore, the results confirm sensitivity of sound speed in ice to its internal microstructure and heterogeneity which are known to affect large-scale ice properties, such as strength, elasticity, permeability, air-sea exchange, habitability, and partitioning of shortwave solar radiation. This motivates future work that would include modeling and measurement of sound speed, attenuation and scattering in natural sea ice, with a goal to develop a remote acoustic sensing technique for sea-ice characterization and, in particular, discrimination between first-year and multi-year ice types. Measurements of sound speed were made on laboratory-grown ice samples serving as proxies for two types of sea ice with different microstructure. The first one, congelation ice, has relatively homogeneous structure typical for first-year sea ice. The second one, granular ice, with a more heterogeneous microstructure, was prepared as a proxy for retextured multi-year sea ice. Both samples had approximately equal bulk salinity (12 ppt) to isolate effects of different microstructure. Sound speed was estimated by measuring time of flight of 400 kHz pulses and was found in congelation ice to be about 10% higher than in granular ice. Error bounds were estimated to be within 1% based on same measurements made for plastic material with known sound speed. Therefore, the results confirm sensitivity of sound speed in ice to its internal microstructure and heterogeneity which are known to affect large-scale ice properties, such as strength, elasticity, permeability, air-sea exchange, habitability, and partitioning of ...