Determination Of Elastic Moduli Of Sea Ice

Abstract : For applications of elastic moduli to acoustic prediction models, moduli derived from acoustic measurements are much more appropriate than those derived from mechanical tests. Several researchers have measured sound velocity in ice and some have used these measurements to deduce ice moduli. Velocity measurement techniques include resonance vibration of ice rods, seismic and flexural wave measurement, and propagation of high frequency pulses in core samples. Differences and uncertainties in conclusions to be drawn from these studies are in part related to temperature and salinity properties of the ice and measurement and core handling procedures that have altered the structure of ice from its in-situ condition. These issues indicate the advantages of a pulse type experiment designed to allow measurement of velocities and related ice properties in the field. We present details of one such design including the equipment used and the resulting moduli uncertainties inherent in the method. The theory to be used in interpreting the experimental results will be that derived by Biot for a porous solid. Expressions for the longitudinal and shear velocities in ice were derived assuming a sealed-pore structure, which generally applies to sea ice away from the growing ice/water interface. A pilot experiment is underway at the present time to perfect the procedure and will allow preliminary implementation of the theory. The results from the type of analysis presented here ultimately lead to prediction of the acoustic impedance layers in sea ice, a crucial factor in understanding and predicting acoustic propagation processes involving sea ice. Reprints.