SPATIAL AND SOURCE LEVEL DISTRIBUTIONS OF ICE CRACKING IN THE ARCTIC-OCEAN

This paper reports measurements of the spatial and source intensity le vel distributions of ice cracking events occurring in the rough, centr al Arctic pack ice. These distributions are computed from a total of 9 16 detected events covering approximately 2 h of data distributed over several days during April 1988. Measurements of individual events wer e obtained over the frequency band 16-200 Hz on a 22-e1ement 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 e vents is consistent with a uniform distribution. Source levels from 11 0 to 180 dB//mu Pa-2/Hz at 1 m were measured. The calculated source le vel distribution for all events approximates a linearly decreasing fun ction on a log-dB scale of the number of events versus source level. T he median occurrence of events having source levels within a 1 dB band centered at 110 dB//mu Pa-2/Hz at 1 m was 4 events per square kilomet er per minute. This falls to 10(-2) events per square kilometer per mi nute at 140 dB//mu Pa-2/Hz at 1 m. The mean and maximum numbers of eve nts are two and ten times greater, respectively.