Beamforming shallow water propagation of mid-frequency acoustics on the Chukchi Shelf

Abstract

The shallow water Canadian Basin Acoustic Propagation Experiment (CANAPE 2016–2017) was designed to study the effect of oceanographic variability on the acoustic field in the Arctic. The physics of the acoustic waveguide on the Northeastern edge of the Chukchi Shelf are influenced by dynamic boundary conditions and spatio-temporal fluctuations in temperature/salinity profiles, including the upwelling of Atlantic bottom water, sinking Bering Sea surface water and sub-mesoscale eddy formation. These fluctuations influence the acoustic waveguide characteristics of a persistent sound speed channel centered at 150 m depth. The University of Delaware (UDel) deployed seven oceanographic moorings (OM) perpendicular to the isobaths on the Chukchi Shelf (145–700 m depth). A Naval Research Lab source (S1) was deployed in-line with the OMs, generating Linear Frequency Modulated (LFM) signals in alternating 700–1100 Hz and 1400–4000 Hz bands. A Vertical Line Array (VLA) was deployed in-line and within the span of the OMs. The array aperture spanned the depth of the sound speed channel. Beamforming measurements from the VLA in combination with environmental measurements and 2D PE model output will determine the degree of influence of individual physical oceanography processes on the spatio-temporal structure of the sound channel and internal acoustic wave propagation.