Page 34 - Summer 2018

Canadian Navel Acoustics
taken of the ship’s radar display to allow accurate navigation to the same location the following year (Milne, 1998).
During the year between deployment and recovery, Milne became concerned about the possibility of the release sys- tem failing and arranged to rent the Pisces 1 manned sub- mersible from International Hydrodynmaics Ltd. at a cost of $150,000 (CAD). To raise the necessary funds, a collabo- ration was undertaken among the PNL team, Herlinveaux, Bernie Pelletier (Bedford Institute of Oceanography), and Carlton Ray (Johns Hopkins University). In mid-August 1968, an RCAF C-130 Hercules flew 25,000 pounds of gear and personnel, this time to Thule, Greenland, to meet the CCGS Labrador.
When the team arrived in Baffin Bay, they found a 53-m- high iceberg with an estimated weight of 45 million tons grounded on the 430-m-deep knoll where the RIP had been deployed. The iceberg was rocking with a two-minute pe- riod, and they quickly realized there was no way to safely recover the RIP. The remaining four RIP recoveries went like clockwork, including the one in Norwegian Bay with 5-feet (1.5-m)-thick 10/10ths ice cover. Before they triggered the explosive bolt to initiate the Norwegian Bay recovery, the icebreaker first had to break a path to the RIP location and then break up ice in a quarter-mile (450-m)-diameter area to allow for the float and dye to be spotted. They also went ashore in Grise Fjord and Pond Inlet and recorded under- water sounds from narwhals from a small boat (Watkins et al., 1971). Using the Pisces, they were able to photograph one of the RIPs while it was still on the ocean bottom (Figure 5). Although the grounded iceberg eventually left Baffin Bay, a heavy swell prevented the safe launch of the Pisces to inspect the RIP deployment site. Thus the fifth RIP was never recov- ered. The RIP systems worked extremely well despite com- ponent failures that limited the recording periods to 3-11 months (Ganton et al., 1970).
Summary
The stories told in this article about acoustic mine and tor- pedo countermeasures, oceanography and the acoustics of antisubmarine warfare, development of a variable depth sonar, and Arctic acoustics are only a few of the dozens of interesting stories arising from Canada’s two naval acoustics research laboratories, the NRE and PNL. Other scientific stories include corrosion prevention by cathodic protection, hydrofoil vessel development, computational acoustic mod- els for reverberation and transmission loss, and explosive echo ranging (in collaboration with the RCAF and other
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maritime air forces worldwide). Oceanographic studies with direct bearing on naval acoustics included fluid dynamics research on turbulent microstructure and internal waves, temperature and salinity surveys, and drift bottle studies of surface currents. Essential to the success of the work was the feeling of camaraderie and excitement about working to- ward a common goal, a sentiment that persists to this day in the remaining Canadian naval acoustics research laboratory, now called the DRDC Atlantic Research Centre.
References
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Ganton, J. H., Dennison, G. N., Burroughs, W. H. M., and Milne, A. R. (1970). Recording Instrument Package (RIP) for Long Term Underwater Measurements in the Arctic. Report 70-4, Defence Research Establishment Pacific, Victoria, BC, Canada. Available at http://acousticstoday.org/rip. Accessed February 15, 2018.
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Longard, J. R. (1993). Knots, Volts, and Decibels: An Informal History of the Naval Research Establishment, 1940-1967. Defence Research Establish- ment Atlantic, Dartmouth, NS, Canada.
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Milne, A. R. (1966). A seismic refraction measurement in the Beaufort Sea. Bulletin of the Seismological Society of America 56, 775-779.
Milne, A. R. (1998). Arctic under-ice acoustics. In Chapman, R. P. (Ed.),