Japan Marine Sci. and Technol. Ctr., 2-15 Natsushima-cho, Yokosuka 237, Japan
Natl. Defence Acad. of Japan, Yokosuka 239, Japan
For the design of underwater acoustic equipment, it is very important to estimate the sound absorption, especially since the longer the propagation range, the greater the effect of sound absorption. Generally, the equations of Thorp, Schlkin, and Marsh and Francois and Garrison are often used for the determination of sound absorption, but these equations yield values that are different from each other. So, the signal level from the data transmitter (center frequency: 20 kHz) of the deep submergence vehicle ``Shinkai 6500'' were measured in detail on the mother ship. The dives for this investigation were carried out at a maximum depth of 6500 m in the northwest Pacific area. It is found that Francois and Garrison's equation was comparatively suitable for the measured data.