Evaluation of Acoustic Positioning of Underwater Vehicle From Seabed Lander System in an Ocean Experiment

Abstract In Japan Agency for Marine-Earth Science and Technology (JAMSTEC), a seabed lander system has been developed for observation at the deepest parts of the ocean up to 11,000 meters depth. In order to expand the observation area and function of the lander, a small underwater vehicle system, which is launched from the lander, is under development. The vehicle is currently tethered to the lander with electrical cable. In the future it is planned that the vehicle will cruise without the tether cable as an autonomous underwater vehicle (AUV). Then the vehicle is positioned by the lander and communicate with that acoustically. The lander has an acoustic communication and positioning system, with which the lander communicates with both its mother ship on sea surface and the vehicle. At the same time the lander measures the relative position of the transmitter on the mother ship and the vehicle with the synchronization signal of the acoustic communication packet using super short baseline (SSBL) method. An ocean experiment was conducted in a sea area, the depth is about 100 meters, and the acoustic positioning of the vehicle from the seabed lander was evaluated. The lander was placed on the seabed and the vehicle was hung from a ship or cruised around the lander. The lander was equipped with a horizontally planer receiver array which consists of five receivers in order to process SSBL positioning. The acoustic system has a chip scale atomic clock (CSAC) and the real time clock of the vehicle was precisely synchronized with that of the lander. Then the measurement of the distance was achieved with one-way propagation time of the acoustic signal. The evaluation was conducted with receiver arrays of two sizes. The positioning was performed with sub-meter order precision.