Abstract:
Array processing on underwater acoustic arrays traditionally ignores three-dimensional aspects of acoustic propagation. In shallow-water environments with sloping seafloors, paths of acoustic energy will ``bend'' out of the vertical plane containing the source and receiver, creating an acoustic field that may be significantly different from that predicted with a two-dimensional propagation model. Consequently, array processors such as conventional beamformers (CBF) or matched-field processors (MFP) may suffer serious localization errors and correlation degradations when arrays are placed in these environments. This study examines the effects of the two-dimensional propagation assumption on array processor (CBF on horizontal arrays, CBF and MFP on vertical arrays) performance when the field is actually three-dimensional. Computer simulations for the ASA benchmark penetrable wedge were used to systematically quantify degradations as a function of wedge angle, water depth, and distance from the array along a cross-slope track. Three-dimensional effects were also demonstrated experimentally for cross-slope source tow data (bottom slope=4--8 deg) recorded on a vertical line array during the fourth shallow-water evaluation cell experiment (SWellEX-4) off San Clemente Island near San Diego. In both cases, localization improvements obtained by incorporating known three-dimensional effects into the matched-field processor were determined. [Work supported by ONR/NRaD.]