Sound Pulse Propagation in a Weakly Range Dependent Shallow Ocean

Abstract

In a weakly range dependent shallow ocean environment, sound propagation can be described effectively in terms of local intrinsic modes [J. M. Arnold and L. B. Felsen, to be published in Wave Motion], which follow lateral trajectories, behave like adiabatic modes where these can be defined, but also accommodate uniformly the transition through cutoff from the adiabatic to the radiative regime. Intrinsic modes yield exact solutions away from the coastline in an isovelocity wedge shaped ocean above an isovelocity fluid bottom [J. M. Arnold and L. B. Felsen, J. Acoust. Soc. Am. 76, 850–860], and therefore render that configuration important for establishing the validity of various analytical and numerical models. Line source excited pressure field calculations by intrinsic modes in the frequency domain [E. Topuz, L. B. Felsen, and J. Yaniv, J. Acoust. Soc. Am. Suppl. 1, 76, S11, 1984] are now generalized to accommodate pulse signals with Gaussian envelope. As in the time harmonic case, the transient intrinsic modes behave adiabatically downslope from cutoff but pass smoothly through the upslope cutoff transition. Their behavior is compared with that of pulsed normal modes in a constant-depth ocean and provides insight into the effect of weak range dependence on transient modal propagation. [Work supported by ONR Ocean Acoustics].