Generation of multiple direct paths and resulting interference patterns during an experiment conducted during summer 2008 off the coast of Hawaii (KAM08).

Abstract

During the KAM08 experiment 3 h of continuous transmissions (10–20 kHz) were made between a ship‐based source and a moored vertical array. Direct path data show modulations that indicate both constructive and destructive interference of acoustic rays. These interference patterns are likely due to multiple direct paths, which arise from refractions of the signal from different portions of the thermocline. The single bottom‐interaction does not show multiple paths, possibly due to a steeper angle of interaction with the thermocline. Multiple thermistor strings show the spatial and temporal changes in thermocline for this geometry. The observed thermocline variations are used to approximate the conditions under which the multiple direct paths were observed. By using ray‐based and parabolic equation models, the interface conditions necessary for generating the multiple direct paths are investigated. Results show that modulations in the spatial and temporal variability of the thermocline are a potential forcing mechanism for the observed interference patterns. [Work supported by ONR.]