J. Robert Fricke
Dept. Ocean Eng., Cambridge, MA 02139
An estimate of total ice mass in the Arctic is an important parameter for global climate studies, but there are no direct means for providing this information. A surrogate measurement, spatial integration of ice thickness, is being pursued by several groups using active acoustic and electromagnetic methods. As a complement to these efforts, the passive estimation of ice thickness using ambient noise caused by thermal and mechanical stress cracks in the ice sheet is focused on. The acoustic signal received from propagating stress cracks is the convolution of an elemental fracture source function and the spatial distribution function (array) of the propagating crack. This analytic result predicts a tonal spectral component of O(1 kHz) that relates directly to ice thickness. Experimental data collected in the Beaufort Sea during the spring of 1994 demonstrates the presence of this spectral peak, which correlates well with the measured ice thickness at the site.