Hovering type AUV “ Tuna-Sand ” and its surveys on Smith caldera in Izu-Ogasawara ocean area

During the operation of and AUV in the ocean, it is necessary to monitor the vehicles position and the status in real time to prevent accidents that may occur abrupt changes in oceanic condition. Therefore a support ship should follow and monitor the AUV during survey. The ship operation costs are high and it is inefficient use if only one AUV dives during a survey. We developed a new survey method for multiple AUVs to make effective use of ship time. In our survey method, two cruising AUVs (AE2000a and AE2000f) pass through approximately the same route and observe the seafloor at a high altitude. One hovering type AUV (Tuna-Sand) navigates and takes pictures of seafloor at a low altitude. The ship follows the two cruising AUVs and sends the command by acoustic communication as necessary. Then an SSBL device on a moored buoy localizes Tuna-Sand and sends vehicle's position and status to the ship by satellite communications. To avoid sound wave interference, sufficient time gap is added between signal transmissions and the GPS time is used for synchronization. The Tuna-Sand AUV observed on Smith caldera in Izu-Ogasawara ocean area in two dives using our survey method. In first dive, the vehicle surveyed for about 2 hours and took 170 pictures of the seafloor. In second dive, we succeeded that AE2000a, AE2000f and Tuna-Sand dived and surveyed on the caldera at same time. The results obtained during the survey are described in detail in this paper.