Using CT and Ultrasound to Measure Sea Ice Core Structures

• Main Author: Parsons, Nathaniel James
• Other Authors: Prior, David
• Format: Thesis
• Language: English
• Published: University of Otago 2019
• Subjects: Sea Ice; CT; Ultrasound; Structure; ice core; Sea ice
• Online Access: http://hdl.handle.net/10523/9852

Sea ice is a complex, multi-layered material, who’s microscopic properties are vital for understanding its macroscopic properties and interactions with the environment. Traditional methods for studying its tructure tend to be destructive in nature and require extraction of samples, changing its properties from its in-situ state. This aim of this thesis was to explore the use of CT and ultrasound on a sea ice core as a means of solving some of these issues. The use of a medical-CT scanner to derive a density profile for the core proved to be quick and easy process producing values ranging from 824 kgm-3 to 917 kgm-3. Time of flight ultrasound measurements, using a 500 kHz pulse, were conducted around the core with calculated velocities for the first two arrivals being between 3100 ms-1 - 3900 ms-1 for the first arrival and 1850 ms-1 - 2100 ms-1 for the second arrival. A velocity anisotropy was observed with both arrivals sharing the same pattern and data for the first arrival was turned into a colour map. A thick section of the entire core was done to generate a structural diagram and thin sections were made in order to make c-axis measurements. P and S-wave velocities were modelled from the c-axis measurements. The data was correlated showing distinct changes in the density profile, ultrasound velocity and velocity anisotropy matching the changes in structural layers in the core. Finally, the first arrival was concluded to be a P-wave. However, the second arrival identification was more difficult due to the velocity matching an S-wave but its velocity anisotropy matching a P-wave. This was argued to potentially be a Biot slow wave.