Toshio Tsuchiya Yasutaka Amitani Hiroshi Ochi
Deep Sea Technol. Dept., Japan Marine Sci. and Technol. Ctr., 2-15 Natsushima-cho, Yokosuka, 237 Japan
Natl. Defense Acad., 1-10 Hashirimizu, Yokosuka, 239 Japan
An accurate equation of sound velocity in seawater is a very important factor for ocean acoustic tomography according to acoustic travel time across the ocean. A sound velocity equation has been examined in a laboratory under various values of temperature, salinity, and pressure by Wilson, DelGrosso, Chen, and Millero. However, as direct measurement in the deep-sea area is very difficult, these data have been very limited. Therefore, recently the sound velocity was measured directly more than 50 times from the surface to a depth of over 6000 m by a sing-around sound velocimeter installed in the manned deep-sea research submergence vehicle ``SHINKAI 6500'' of the Japan Marine Science and Technology Center. Data were obtained with temperature, salinity, and pressure values in the western Pacific Ocean area. Then, the measured data were compared with the calculated values of the equation of Wilson, DelGrosso, Chen, and Millero. The comparison result indicated a trend: Sound velocity in the deep sea is greater than values of various equations according to the pressure effect.