MESOSCALE VARIATIONS IN THE DEEP SOUND CHANNEL AND EFFECTS ON LOW-FREQUENCY AND PROPAGATION

Spatial variability in the deep sound channel is measured in a large-scale oceanographic survey, and its effects on sound propagation are studied in a numerical experiment. The oceanographic data are obtained from a near-synoptic, multiship survey of upper layer thermal structure in the Northwest Pacific which is extended to 4000m depth using an objective extrapolation model and historical hydrographic data. The extrapolated temperature profiles are converted to salinity and sound velocity profiles using mean temperature-salinity curves, and the resultant sound velocity structure is dominated by mesoscale features which are apparent as large vertical excursions of the channel depth. A numerical experiment that models low-frequency (50 Hz) sound propagation in this model ocean shows that the standard deviation of an ensemble intensity field rises to a plateau of about 5.5 dB in several tens of kilometers, indicating a mesoscale multipath effect with a shorter saturation range than the corresponding internal wave induced effect. Statistics of the intensity at a point receiver are shown to be slightly non-Gaussian, with the non-normal deviation decreasing with depth. © 1979, American Association of Physics Teachers. All rights reserved.