Acoustic propagation in shallow water

Abstract

Acoustic transmission loss measurements using an airborne technique developed by Urick were made on the East Coast of the United States and in the North Sea. In addition to effect of site on transmission characteristics, the effect of season, sound frequency, source depth, and direction of propagation with respect to the bathymetry were also investigated. Generally, a correlation between transmission loss and the sound velocity profiles were observed; the more negative the sound speed gradient, the higher the transmission loss. Specifically, transmission loss in the summer season was consistently higher than in the winter season. The variation from site to site was large and water column dependent. The effect of direction (bathymetry) indicated sound traveling upslope suffers the highest loss; sound traveling downslope the lowest, and in constant water depth, an intermediate value. The effect of short time intervals on transmission loss was found to be negligible, with the observed variation fitting very closely the expected variation in source level due to explosive source charge variation. There was no apparent dependence on source depth and the frequency effect was a monotonic one, with higher losses occurring at higher frequencies. [Work supported by the Naval Air Systems Command.]