We have developed an Autonomous Underwater Vehicle (AUV), which can be used for lake environment monitoring. The length of the AUV is 2m, its weight in air is 180kg, and its maximum speed in water is 2 knots. It has two major missions: one is to monitor plankton distribution in the epilimnion by using its on-board submersible microscope, and the other is to monitor water quality 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 (RN) by ultrasonic waves, and subsequently transferred from the R/V to our base institute (Lake Biwa Research Institute) by a satellite mobile phone data link.
We use the super short baseline to determine the spatial position of Tantan in water, and a differential GPS when on the water surface. Tantan is equipped with an Acoustic Doppler Current Profiler of 1,200 kHz to obtain its speed relative to the lake bottom. It also has 5 forehead echo sounders and one upward echo sounder of 175 kHz to detect obstacles, and avoid collision. A digital video camera (SONY EVI-370) is located behind a clear dome at the front of the AUV and is used to provide a forward view. Also, a submersible microscope (BFDR) is attached to detect plankton and other water-born objects. Microscope images are transferred to the R/V where basic plankton statistics such as species type and sizes can be automatically determined using image processing and pattern recognition techniques.