Contribution of bottom-refracted sound to oceanic sound propagation

Abstract

In the deep ocean, sound from an underwater source is channeled in the SOFAR channel to form a long series of convergence zones. These may be influenced by bottom reflections when the propagation occurs down a sloping ocean floor. Experiments [W. M. Carey, J. Acoust. Soc. Am. 79, 49 (1986)] show important residual intensities (∼10 dB excess) between convergence zones whose origin could not be conclusively explained by downslope conversion, but could have been due to ‘‘refraction’’ (bottom penetration). Earlier pulse return experiments by Christensen etal. [J. Acoust. Soc. Am. 57, 421 (1975)] conclusively established the presence of bottom penetration effects in the presence of upward-refracting sound-speed gradients in ocean-floor sediments from a flat, deep (4000-m) ocean floor. In the present model calculation, carried out for the Christiansen deep-water case by using normal-mode and fast-field models, the influence of a shear-supporting, upward-refracting ocean floor on oceanic sound propagation, including the long-range presence of inter-convergence zone residual sound fields caused by bottom penetration is demonstrated. [Work supported by the ONT.]