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Underwater Glider for a Long-Term Virtual Mooring JAMSTEC Glider Able to Monitor Ocean From Seafoor for Over a Year By Dr. Kenichi Asakawa • Dr. Masahiko Nakamura T he ocean has a strong infuence on global climate. With a heat capacity thousands of times greater than that of the atmosphere, it absorbs about 30 percent of the artifcially emitted carbon dioxide. The ocean environment is monitored by many means, including profling foats, moored buoys, ships and satellites, but due to the ocean's vastness, gathering suffcient data on how it affects Earth's climate is still diffcult. To help address these gaps, the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) began developing in 2009 a prototype underwater glider for virtual mooring, designed to stay on station and monitor designated waters from the seafoor to the sea surface for more than one year. The glider, named Tsukuyomi after a Japanese god from old myths who governs the moon and nights, can sleep on the seafoor to extend its monitoring duration. The goal of this project, conducted in cooperation with Research Institute for Applied Mechanics, Kyushu University, is to assess the possibility of underwater gliders for use in virtual mooring. Although it is still in an early development stage, Tsukuyomi has proven its basic gliding performance in tank tests and the frst sea test in March. The team is now expanding the glider software so it can carry out long-term monitoring in designated waters. Existing Observing Platforms and Glider Capabilities Even with 3,600 foats distributed worldwide, the Argo project has shortcomings in ocean-monitoring requirements. For example, the Argo foats foat with currents and cannot stay in a designated area where data are needed, and it is diffcult to increase their number to assess all oceans with adequate density. In addition, a widespread change in seawater temperature has been observed even in waters deeper than the foat's maximum profling depth of 2,000 meters, which A diagram of Tsukuyomi operations. underscores the necessity of monitoring the ocean environment in deeper waters. Other methods, such as moored buoys and research vessels, also have their benefts and shortcomings. Moored buoys can conduct long-term monitoring at a fxed point, but they cannot monitor the sea environment from the seabed to the sea surface, as they generally monitor waters shallower than several hundred meters. Increasing the number of deployed buoys is also impractical because of their construction and maintenance costs. Maintenance of buoys also requires large vessels, and research vessels provide a limited range of data. Underwater gliders have recently attracted attention and have been used widely because they can travel autonomously over long distances gathering ocean data that cannot be obtained otherwise at a reasonable cost. However, their operating duration is shorter than one year. They cannot provide long-term data as Argo foats or moored buoys can, and their monitoring areas are generally restricted to coastal areas. To study global environmental change, next-generation ocean observation systems should examine key areas long www.sea-technology.com DECEMBER 2012 / st 15