Oceanographic, topographic, and sediment interactions in deep water acoustic propagation. Part II. Gulf Stream simulations

Interacting low-frequency acoustic propagation effects of range-dependent oceanographic sound-speed profiles and range varying topography, with a fluid sediment layer, are modeled in the Gulf Stream region using a parabolic approximation to the Helmholtz equation. Oceanographic frontal effects, monotonically upsloping and downsloping topographic effects are identified in propagation between reciprocally chosen points on either side of the Gulf Stream at frequencies of 25, 50, and 100 Hz. For propagation from Slope to Sargasso water, surface shadow zone formation is documented, and ensonification of the shadow zone due to low-frequency diffraction. In propagation from Sargasso to Slope water, increased surface ensonification results. Topographic effects include truncation/reflection of deep propagation paths for upsloping topography, and increased depth for water column refraction for downsloping topography. Frequency and source depth-dependent oceanographic and topographic interaction effects are documented for two major propagation regimes: one containing primarily water-column refracting patterns, and one in which bottom-glancing propagation paths dominate sound fields for mid to long ranges.