Abstract
A preliminary analysis of synoptic ambient noise and transmission loss measurements in the ice-free subarctic suggests that the ice edge may be represented as a line source of sound, and that the rate of change of noise level with distance from the ice edge is related to the attenuation coefficient [Diachok and Long, J. Acoust. Soc. Am. 56, S17(A), S50(A) (1974)]. Since the low-frequency attentuation coefficient is a subject of current controversy it was felt that further investigations of the low-frequency transmission-loss data was warranted. Based on synoptic airborne bathythermograph data, transmission loss was computed using range-dependent ray theory and the parabolic equation method. (The latter computations were made by J. Hanna of AESD, Washington, DC). Both sets of computations were found to be in reasonably good agreement with measurements. The observed systematic departure from cylindrical spreading was apparently a consequence of the sound velocity structure. In agreement with the preliminary analysis, the departure from cylindrical spreading could be used to “predict” the rate of change of noise level with distance. For this particular data set ice-edge noise at 100 Hz was apparent up to 400 km from the edge.
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