A new autonomous underwater vehicle designed for lake environment monitoring

We have developed an autonomous underwater vehicle (AUV), Tantan, which can be used for Lake Biwa environment monitoring. The Japanese word Tantan means 'a freshwater explorer'. The length of Tantan is 2 m, its weight in air is 180 kg and its maximum speed in water is 2 knots. Tantan has two major missions. One is to monitor the three-dimensional structure of plankton distribution along thermocline by using its on-board submersible microscope, and the other is to monitor water quality such as dissolved oxygen in the benthic boundary layer by using a CTD instrument equipped with multiple sensors. The obtained data and images are transmitted to a surface research vessel (R/V) by ultrasonic waves as well as stored inside Tantan, and can be subsequently transferred from the R/V to our base institute (the Lake Biwa Research Institute) by a mobile phone data link. Several test experiments have been done in Lake Biwa, and we confirmed that Tantan could move smoothly up and down with an amplitude of 5 m along the isotherm of 15°C, which was the center of thermocline, and also can collect data.