Measurements of 3-dimensional Downslope Acoustic Propagation During the Basin Acoustic Seamount Scattering EXperiment (BASSEX-04)

As part of the North Pacific Acoustic Laboratory (NPAL) 2004 sea-test, the Basin Acoustic Seamount Scattering EXperimnet (BASSEX) was performed. A portion of this test was dedicated to taking towed array measurements of acoustic transmissions from the NPAL source moored off the coast of Kauai. In this paper, several transmissions which show evidence of 3-dimensional propagation are analyzed. Broadband transmissions to a towed array provide the opportunity to examine the spacial and temporal arrival structure of the acoustic propagation. Clear multipath arrivals with times and arrival angles different from the expected 2-dimensional plane of propagation are recorded. These results are presented as well as a hypothoses for how the interaction of the acoustic field and the local bathymetry leads to 3-dimensional propagation. In order to examine the stability of these arrivals, the 20 minute reception is run through a frequency domain adaptive beamformer. Comparison of the eigenspectra with 2 D Parabolic Equation simulations leads to the conclusion that bottom roughness and 3 D propagation are significant factors in explaining the arrival complexity.