High-frequency forward scatter and propagation experiments in the Delaware Bay

Abstract

In order to assess the temporal and spatial coherence of transmitted broadband acoustic signals (1–20 kHz) in coastal environments, two acoustic experiments were performed in the Delaware Bay during March and September 1997. Accompanied by measurements of the ocean volume (temperature and salinity) and sea surface roughness (0- to 0.5-m wave height), these acoustic experiments included reciprocal acoustic transmissions over a large band of acoustic frequencies and during a variety of sea states. The connection between the stability and coherence of the single surface bounce and the sea surface roughness is studied. In the presence of rough seas (and therefore bubbles), the coherence decreases rapidly between reciprocal receptions as sea state increases, while for calm sea states a high correlation exists between them. Some preliminary modeling results using a high-frequency parabolic equation (PE) model are used to interpret this frequency-dependent behavior.