Abstract

Sound speed in the oceans depends on temperature, salinity, and pressure and has large seasonal and spatial variations. The article presents results of negative velocity sur- veys at some locations in Tonkin Gulf with data on temperature and salinity at depths from 0m to 70m, from 01/01/2006 to 01/12/2006. The results show that variation in velocity dur-ing one year in Tonkin Gulf was 27.2 m/s. This is important in determining the velocity of sound when using underwater sound wave technology in the Tonkin Gulf.