Oceanographic Variability in Shallow-Water Acoustics and the Dual Role of the SeaBottom. (Reannouncement with New Availability Information)

摘要

Acoustic propagation in shallow water is an area of major concern to the Navy.The difficulties associated with the use of acoustics in the ocean, however, are aggravated in shallow water. Multipath propagation and extensive boundary interactions, especially with the sea bottom, conspire, along with a host of other phenomena, to produce a highly variable and often unpredictable acoustic field. The responsible mechanisms, and hence the acoustic effects, cover a wide range of temporal and spatial scales. The mechanisms are classified as either deterministic or random, although the two types often act in concert. The sea bottom plays a dual role in shallow-water acoustics. Because of extensive interactions with the sound field, the bottom can severely degrade waterborne propagation. On the other hand, the sea bottom (and subbottom) can provide a seismic path that not only is relatively stable, but exists even under environmental conditions that preclude an effective waterborne path. Propagation in the bottom is particularly significant at very low frequencies, often being more efficient than high-frequency waterborne propagation. The preceding aspects of shallow-water acoustics--viz., variability and dual role of the sea bottom-are illustrated using the results of experiments conducted in diverse geographic areas by the Naval Research Laboratory/SSC and by the SACLANT Undersea Research Centre.... Seismic waves, Scholte waves, Seismic arrays.