ASA 125th Meeting Ottawa 1993 May

1pAO1. Shallow water acoustics research issues.

Robert L. Field

Jerald W. Caruthers

Ronald A. Wagstaff

Stanley A. Chin-Bing

Naval Res. Lab., Stennis Space Center, MS 39529

Propagation of sound in shallow water is complicated by the proximity of the boundaries and interferring noise sources and by environmental variability. Moreover, geomorphic and geoacoustic properties of the seabed play a major role in the character of the propagating signal. Propagation prediction is complicated by the need to use full wave field models versus simpler ray models. Roughness and inhomogeneities of the interfaces and seafloor are important to both forward and backscatter. Multiple interactions with the interfaces cause signal frequency, angle, and time spreads, coherence loss, and out-of-plane effects, and they exacerbate shear and interface wave problems. The practical effects of all this are complications in the reverberation and noise fields and in signal coherence. On the other hand, match-field processing in shallow water provides some benefits (essentially, by taking advantage of multiple images of the target reflected in the boundaries), but achieving a positive net gain is critically dependent on our basic understanding of the multiplicity of detrimental effects. These issues are discussed in terms of their relevancy to acquiring this understanding to support ongoing technology and advanced development programs in the Navy.