Surface-ducted contributions in shallow water sound transmission

Abstract

The relative importance of ducted energy under shallow water isogradient propagation conditions has been estimated using an extension of a shallow water propagation model developed by P.W. Smith Jr. [J. Acoust. Soc. Am. 50, 332–335 (1971)]. The ratio, Ed/Et of the ducted energy to the total energy is theoretically predicted for given environmental conditions. The study shows that for moderately large (greater than 50) range to depth ratios and nominal positive gradients (0.01 to 0.1 sec−1) the surface ducted energy is the dominant feature of shallow water transmission loss. In positive gradient conditions Ed/Et is found to be insensitive to bottom-loss estimation errors. For a wide variety of environmental conditions it is demonstrated that transmission loss for purely ducted propagation does not differ significantly from total transmission loss. The study provides theoretical confirmation of previous heuristic results.