Modelling the effects of pore geometry in shallow glacier ice cores on ultrasonic wave velocity anisotropy.

Velocity anisotropy is commonly observed in measurements of ultrasonic waves travelling through ice cores. In deep polar cores this can be attributed to c axis orientation. However in cores taken from temperate valley glaciers it is likely that the geometry of air and water filled pores has a more significant effect on wave velocity anisotropy than c axis orientation. Previous models used to determine trapped air content from ultrasonic wave velocities presume spherical pores. A new model has been developed taking into account the effect of pore compression and the rotation of non spherical pores on wave velocity. The present study considers velocity changes in response to changes in ice characteristics by waves of different frequency waves. The new model is applied cores from Glacier de Tsanfleuron, Switzerland, which have previously been logged using ultrasonic wave measurements at 2 different frequencies. Ice and pore characteristics are characterised and compared to those determined by dielectric methods.