Arctic ambient noise beamforming and modelling / by Michael Greening.: DR52-12/2-1989E-PDF

"The following report details the work completed to date in characterizing the transients contained in the acoustic noise produced from Arctic pack ice. A simple source detection system capable of finding transients with a high signal to noise ratio was used and an average and median number of transients of 4 and 2 respectively were found per 2-minute sample of data. These transients were shown to be vertically directional with a loss at 50-100Hz of approximately 15dB from 5 to 15 degrees from horizontal and a further loss of 10dB from 15 to 90 degrees. This vertical directivity was also shown to increase slightly with frequency. In examining bottom characteristics to aid in modelling the source propagation, sub-bottom layers at 3m and 15 m deep were found. Although exact measurements of bottom roughness were not obtained, it was observed to be acoustically flat for frequencies of up to 2000Hz."--abstract (page 1).

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