Sound Speed, Reflectivity, Absorption, amd Thermal Diffusivity Measurements inArctic Ice in 1990

摘要

Detailed measurements of internal properties of Arctic ice were made in Spring1990 to relate acoustic properties to the physical properties of the ice. This report presents the procedures, analyses, and results of those studies. Some basic parameters measured in previous field studies were remeasured; consistency between individual experiments strengthens our confidence in the results and the techniques used. Novel techniques were used to measure properties of growing ice, which was later cored, submerged, and remeasured. Results reported here have been summarized in the open literature (Williams et al., J. Acoust. Soc. Am., 92, 2075, 1992). The basic data and their processing are described here in detail. In the ice-growth and submergence study, a 2-m-square hole was cut though the ice canopy. Strings of hydrophones and thermistors were then suspended vertically in the hole, and the water froze around them. Frequent monitoring of ice temperature and the receipt of sound pulses from below, along with salinities determined from ice cores obtained a short distance away, gave insight into the freezing process and the formation of a skeletal layer above the ice/water interface. Periodic measurements of the reflectivity of the growing ice at 37-150 kHz gave further information on the skeletal structure. The sound speed in the skeletal layer varied from that of the water at the ice-/water interface to that of bulk ice at about 3 cm into the ice. Absorption of sound (in decibels per meter) was about three times greater near the interface, decreasing to that for bulk ice at 15-20 cm into the ice. Ice acoustic properties, Reflection, Sound speed, Attenuation, Ice bulk properties, Porosity, Thermal conductivity.