Occurring as a set of 17 chemical elements in the periodic table, rare earth elements such as neodymium are necessary for the development of mobile phones and magnet motors. Although securing rare earth elements is essential for economic growth of all nations, their demand is rapidly expanding among global powers such as Brazil, Russia, India, and China. Rare earth element deposits were discovered in the seafloor near hydrothermal vents in the 1980s. Japan has the sixth largest exclusive economic zone (EEZ) and is abundant in underwater natural resources such as a cobalt and a manganese mine. Because underwater exploration of rare earth elements was deemed unprofitable, the practice was suspended. Current advancements in underwater robotics, however, have led to economic viability in this venture. Such developments have resulted in the increased use of remote sensing with sonars on unmanned underwater vehicles.
The Japan Agency for Marine-Earth Science and Technology (JAMSTEC) developed a cruising autonomous underwater vehicle (AUV) known as Urashima. This AUV performed its first sea trial in 2000, and cruise for 317 km without recharging or refueling in 2005 as a world record at the time. The first mission of Urashima was a vast sea exploration to investigate worldwide environmental crises such as global warming. However, the purpose of these missions has since then shifted primarily to the exploration of underwater natural resources. In addition, JAMSTEC developed a synthetic aperture sonar on a neutral buoyancy towfish in 2010. This underwater exploration system, known as Kyouryuu, scanned Wakamiko caldera at the sea bottom in Kagoshima Bay where volcanic activity was evident. Numerous hot-water flows from hydrothermal vents were clearly recorded. In addition, many dormant chimneys were detected. These features provide important data for estimating the distribution of hydrothermal vents and chimneys in addition to their transitions.