Applicability of the parabolic equation method (PE method) to sound propagation modeling

Abstract

The PE method is the latest major development in the field of acoustic modeling [S.T. McDaniel, J. Acoust. Soc. Am. 57, 307–311 (1975); R.M. Fitzgerald, J. Acoust. Soc. Am. 57, 839–842 (1975)]. In the investigation described here, the PE method has been applied to various propagation cases in both deep and shallow water, with and without bottom absorption, and for both range-dependent and range-independent environmental conditions. It is shown that the predicted transmission losses provided by the PE program are in close agreement with beth experimental data and with predictions obtained from mode and ray programs. However, there are practical limitations to the PE method. For instance, as shown theoretically and confirmed by the numerical tests, the method cannot handle steep sound speed gradients without running into excessive calculation times. This means that in practice the PE method is inapplicable to acoustic modeling in shallow water, where there are big changes in sound speed at the water/bottom interface. The major advantage of the method is the simple way in which it handles range dependence. We may therefore conclude that the PE method is primarily applicable to low-frequency acoustic modeling in deep water (no bottom effects) under range-dependent environmental conditions.