A case study on the influence of internal waves on sound propagation in the sea

Abstract

Internal waves are identified off Thailand in the Andaman Sea from sound speed structure computed with time series of temperature and salinity data off Thailand. The influence of these internal waves on underwater sound transmission is analyzed. Sound speed changes with depth and range are used for ray plotting in the internal wave domain. The internal waves seem to have acted as an acoustic lens on the sound beam, producing alternate shadow zones with converging and diverging ray patterns. The sound intensities are computed at selected points in the convergence/divergence zones after incorporating the phase addition among direct and reflected rays. This has produced an intensity contrast of 23 dB with phase in contrast to −8 dB without phase. The coherent additions of sound intensities appear to represent a better picture in the internal wave field for frequencies up to 10 kHz.