Michael V. Greening
Jasco Res. Ltd., 9865 W. Saanich Rd., Sidney, BC V8L 3S1, Canada
Defence Res. Establishment Pacific
This paper reports measurements of the spatial and source intensity level distributions of ice cracking events occurring in the rough Arctic pack ice. These distributions are computed from a total of 916 detected events covering approximately 2 h of data distributed over several days during April 1988. Measurements were obtained over the frequency band 4--200 Hz on a 22-element vertical array and a 7-element horizontal array deployed below the Arctic pack ice in 420 m of water. The observed spatial distribution of detected events is consistent with the case where ice cracking events are uniformly distributed. Source levels from 110 to 180 dB//(mu)Pa at 1 m were measured. The calculated source level distribution for all events approximates a linearly decreasing function on a log-dB scale of the number of events versus source level. The median, mean, and maximum numbers of events occurring per square kilometer per minute over a 1-dB band of source levels centered at 110 dB//(mu)Pa at 1 m are approximately 4, 8, and 40, respectively.