Propagation of sound in oceans

Abstract

The present project work studies the characteristics of the sound speed profiles in the Arabian Sea and the Bay of Bengal. Since the sound speed in the ocean depends on the temperature and salinity, the vertical profiles of temperature and salinity were also examined in both the Arabian Sea and the Bay of Bengal. To compute sound speed FORTRAN program was used. The sound speeds were computed from the temperature, salinity and depth data at standard oceanographic depths at one location each in the Arabian Sea (14.5oN, 63.5oE) and the Bay of Bengal (14.5oN, 87.5oE). The vertical profile of sound speed in the Arabian Sea showed the presence of surface duct in the upper 50 m which is very important for the submarine SONAR operations. The SOFAR channel axis was at 300 m and the effective wave guide lies between 100 m and 1250 m whereas the vertical sound speed profile in the Bay of Bengal showed the presence of surface duct in the upper 60 m and the SOFAR channel axis at 300m. The effective deep wave guide was between the depths 100 and 1200 m. Again analyzing vertical profiles of temperature and salinity it is found that the surface duct seen in the Arabian Sea sound speed profile in the upper 50 m was due to the presence of isothermal and isohaline layer. Sound speed increases here with increase in depth. Below 300 m the depth is more dominant than temperature and salinity which ultimately increases the sound speed while in the Bay of Bengal, strong surface duct was seen due to the sharp increase of salinity in the isothermal layer. Sound speed increases below 300 m, as it was in the same case of Arabian Sea. Due to lower salinity of Bay of Bengal, it will have always lower sound speed values at any given depth.