Modeled acoustic propagation through an ice edge eddy in the East Greenland Sea Marginal Ice Zone

Abstract

A detailed modeling study of the relationship between the various oceanographic features of a cyclonic eddy located at the ice edge off the coast of northeastern Greenland and the eddy's effects on the propagation of acoustic energy is presented. The effects of the eddy on acoustic propagation as a function of location, depth, and frequency of the acoustic source and depth of the receiver for nominal frequencies of 50 Hz and 1 kHz are discussed. Significant differences sometimes greater than 20 dB in the acoustic field were observed for variations in any of the source and receiver parameters. The sound speed structure of the eddy makes propagation loss and acoustic modes very dependent on direction and location. A significant finding is that the interior environment of the eddy can generate a frequency dependence on propagation loss so that 1 kHz sustains a loss as much as 20 dB smaller than does 50 Hz, i.e., dispersion phenomenon. A similar propagation loss anomaly was observed and appears to be due to a combination of marginal ice zone (MIZ) fine structure and interference patterns created by reflections from the sea surface. Such an anomaly can exist in the MIZ with or without the eddy environment. Both of these frequency anomalies are a function of source and receiver depth. Low‐frequency (50 Hz) energy in the presence of the eddy can experience stronger downward refraction and thereby possibly suffer greater bottom interaction than high frequencies (1 kHz). As compared to the noneddy environment, propagation in the presence of the eddy, for any of the source and receiver depths studied, can result in changes in the levels and distribution of energy in the acoustic field by more than 10 dB as well as changes in the mode of propagation of some rays (e.g., refracted/surface‐reflected to refracted/refracted).