PREDICTABILITY OF ACOUSTIC INTENSITY AND HORIZONTAL WAVE-NUMBERS IN SHALLOW-WATER AT LOW-FREQUENCIES USING PARABOLIC APPROXIMATIONS

Accuracy of relative intensity and horizontal wave-number predictions from parabolic approximation models of shallow water, low-frequency (l ess than 100 Hz) acoustic propagation problems is examined. Effects of input parameter uncertainties and basic approximations in parabolic e quation models are investigated. Environmental parameters and uncertai nties considered correspond generally to those from a recent New Jerse y Shelf experiment. Parameter uncertainties are found to impose the gr eatest limitations on prediction accuracy, with sediment sound-speed u ncertainties causing the largest restrictions. Issues associated with modeling the sediment sound speed, such as using isospeed layers to ap proximate sound-speed variations, are also resolved. Weak range depend ence in the channel depth and sound speed, of similar type as at the e xperiment site, is found to be well approximated by range-independent models. Comparisons of the experimental results with model predictions illustrate how parameter uncertainties may have significant effects.