Deep sea current measurement with 3-D Sing-around acoustic Doppler current meter

A deep sea floor (about 1960 m) in the Suruga Trough that is located 150 km away to south-east of Tokyo, Japan, is known to have a distribution of current ripples. It implies that there is strong current and bottom sediment transportation near the floor. In 1990, the authors measured current velocity in the bottom layer using a mooring system with a 3D Sing-around acoustic Doppler current meter, an electromagnetic current meter and a 8 mm-video camera for a week. In 1992, in order to determine the spatial distribution of current ripples and current structures, dives of a manned submersible Shinkai 2000 that was equipped with the 3D Sing-around Acoustic Doppler current meter were carried out. The results obtained from the observations are as follows: (1) A strong movement of the sediment and daily change of strong current are observed by the mooring system current meters and the video camera. (2) The authors have obtained cross-the-trough distribution of current ripples at the sea floor of the Suruga Trough by dives of Shinkai 2000. (3) 3D current measurements near the bottom reveal that the percentage of vertical component for absolute velocity depends on the mean velocity.