Computed time-reversing array retrofocus azimuth size in a dynamic bottom-varying shallow-water sound channel

Abstract

A time-reversing array (TRA) can retrofocus acoustic energy to the location of its original source even when the acoustic environment is complex and unknown. However, vertical TRA performance in the azimuth direction is entirely determined by variations in the water column and bathymetry. Predictions of TRA retrofocusing performance in this study are made with a parabolic equation code (RAM by M. D. Collins). In addition to the sensitivity of TRA retrofocusing to time variation in the water column of a shallow-water sound channel, this study addresses the azimuth size of the retrofocus. Interestingly, the azimuthal retrofocus size decreases with increasing range when internal waves are present. However, azimuthal retrofocusing is degraded as the acoustic propagation from the TRA is influenced by internal-wave dynamics within the water column. The range at which the effect of bottom variability on the retrofocus azimuth size matches that of internal waves is characterized. The internal waves are based on measured oceanic statistics drawn from the SWARM ’95 experiment. Retrofocusing results are presented for a variety of ranges and acoustic frequencies. [Work supported by the Office of Naval Research, Ocean Acoustics.]