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Modeling Uncertainties in the Prediction of the Acoustic Wavefield in a Shelfbreak Environment

Lermusiaux, P.F.J., C.-S. Chiu and A.R. Robinson, 2002. Modeling Uncertainties in the Prediction of the Acoustic Wavefield in a Shelfbreak Environment. Refereed invited Manuscript, Proceedings of the 5th International conference on theoretical and computational acoustics, May 21-25, 2001. (Eds: E.-C. Shang, Q. Li and T.F. Gao), World Scientific Publishing Co., 191-200.

The uncertainties in the predicted acoustic wavefield associated with the transmission of low- frequency sound from the continental slope, through the shelfbreak front, onto the continental shelf are examined. The locale and sensor geometry being investigated is that of the New England continental shelfbreak with a moored low-frequency sound source on the slope. Our method of investigation employs computational fluid mechanics coupled with computational acoustics. The coupled methodology for uncertainty estimation is that of Error Subspace Statistical Estimation. Specifically, based on observed oceanographic data during the 1996 Shelfbreak Primer Experiment, the Harvard University primitive-equation ocean model is initialized with many realizations of physical fields and then integrated to produce many realizations of a five-day regional forecast of the sound speed field. In doing so, the initial physical realizations are obtained by perturbing the physical initial conditions in statistical accord with a realistic error subspace. The different forecast realizations of the sound speed field are then fed into a Naval Postgraduate School coupled-mode sound propagation model to produce realizations of the predicted acoustic wavefield in a vertical plane across the shelfbreak frontal zone. The combined ocean and acoustic results from this Monte Carlo simulation study provide insights into the relations between the uncertainties in the ocean and acoustic estimates. The modeled uncertainties in the transmission loss estimate and their relations to the error statistics in the ocean estimate are discussed.