Short-range acoustic propagation using mobile transmitters under Arctic ice cover
Doyle, Liam J.
Reeder, D. Benjamin
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Using mobile acoustic transmitters, acoustic propagation over short ranges was evaluated. Four Expendable Mobile ASW Training Targets (EMATTS) were deployed over two separate days to run at depths of 183, 91, and 46 meters. Emitted frequencies in the bands of 950 to 1150 hertz and 2800 to 3000 hertz were recorded by omnidirectional receivers at ranges out to 10 kilometers. Sound speed profile data was also measured on site. Transmission loss models were created as a baseline at the various depths, ranges and frequencies. The recorded acoustic data was then analyzed to provide measured transmission loss profiles, including variability at range, in order to provide a comparison to the modeled data. A significant finding was the inability of the modeling software to accurately predict the surface water/ice scattering and absorptive effects on transmitted sound. In addition, sound speed variability by range (usually considered range-independent over short distances) was shown to have a strong effect on transmission. This was demonstrated by very large variances in received sound level (on the level of 30 to 40 decibels) at the same range and depth but different directions.
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