Sensitivity of acoustic propagation to uncertainties in the marine environment as characterized by various rapid environmental assessment methods |
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Authors: | Sean Pecknold John C Osler |
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Institution: | (1) DRDC Atlantic, 9 Grove St., Dartmouth, NS, Canada, B2Y3Z7;(2) NATO Undersea Research Centre, Viale S. Bartolomeo 400, 19126 La Spezia, SP, Italy |
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Abstract: | Accurate sonar performance prediction modelling depends on a good knowledge of the local environment, including bathymetry,
oceanography and seabed properties. The function of rapid environmental assessment (REA) is to obtain relevant environmental
data in a tactically relevant time frame, with REA methods categorized by the nature and immediacy of their application, from
historical databases through remotely sensed data to in situ acquisition. However, each REA approach is subject to its own
set of uncertainties, which are in turn transferred to uncertainty in sonar performance prediction. An approach to quantify
and manage this uncertainty has been developed through the definition of sensitivity metrics and Monte Carlo simulations of
acoustic propagation using multiple realizations of the marine environment. This approach can be simplified by using a linearized
two-point sensitivity measure based on the statistics of the environmental parameters used by acoustic propagation models.
The statistical properties of the environmental parameters may be obtained from compilations of historical data, forecast
conditions or in situ measurements. During a field trial off the coast of Nova Scotia, a set of environmental data, including
oceanographic and geoacoustic parameters, were collected together with acoustic transmission loss data. At the same time,
several numerical models to forecast the oceanographic conditions were run for the area, including 5- and 1-day forecasts
as well as nowcasts. Data from the model runs are compared to each other and to in situ environmental sampling, and estimates
of the environmental uncertainties are calculated. The forecast and in situ data are used with historical geoacoustic databases
and geoacoustic parameters collected using REA techniques, respectively, to perform acoustic transmission loss predictions,
which are then compared to measured transmission loss. The progression of uncertainties in the marine environment, within
and between different REA categories, and the consequences on acoustic propagation are examined. |
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