Predictability of acoustic intensity in shallow water at low frequencies using parabolic approximations

Abstract

The accuracy of predictions for acoustic intensity in shallow water from parabolic approximation models are carefully examined. First, accuracy comparisons are made between analytic solutions to the Helmholtz equation and parabolic equations for propagation in a Pekeris waveguide. The parameter dependencies of the interference patterns for frequencies below 100 Hz are described. Calculations from the IFD implementation of parabolic equations are also compared with the analytic solutions. Agreement between the analytical and numerical results is very good, providing that appropriate initial conditions are employed. Sensitivities to input parameters are examined by observing the variations in the predicted fields and intensities as the parameters are changed. The parameters include those specifying the depth and range properties of the geoacoustic bottom, sound-speed profile, and spatial features of the waveguide. Magnitudes of parameter variations are selected consistent with a recent Hudson Canyon experiment. Comparisons of the experimental results with model predictions are discussed. One conclusion is that input parameter uncertainties, even though relatively small for this experiment, can in some cases significantly affect the predictions. [Work supported by ONR.]