Japanese scientists have successfully tested an autonomous wave glider to monitor volcanic activity on the island of Nishinoshima, where eruptions have been ongoing since November 2013.

On October 20, researchers from the Kobe University Graduate School of Science, the University of Tokyo Earthquake Research Institute and the Japan Agency for Marine-Earth Science and Technology launched the volcano-monitoring system on a trajectory that circles Nishinoshima. The system autonomously sailed around Nishinoshima in a circular path with a 5km radius and was successfully recalled the following day.

Researchers prepare to launch the wave glider. Image credit: Kobe University.Researchers prepare to launch the wave glider. Image credit: Kobe University.The wave glider consists of a float above water connected by a 5.8m umbilical cable to an underwater glider that propels the vessel. The float also carries several cameras, a device to detect earthquakes and air vibrations, a GPS tsunami meter and two sets of transmission devices, including a satellite communications terminal to transmit the observation data via satellite.

The device is also equipped with two microphones at the front and back to detect air vibrations, and a hydrophone is attached to the underwater glider to identify sonic waves at a depth of 6m. Four time-lapse cameras are attached to the wave glider at 90-degree intervals to enable continuous visual observation of Nishinoshima over long periods of time and capture images across 360 degrees. The up-and-down motion of the wave glider can be adjusted to within 5cm using the Doppler shift of the GPS carrier wave.

Outfitted with these technologies, the wave glider was able to continuously record data while it circled Nishinoshima. The team confirmed that their sonic observation was accurate enough to detect earthquakes and air vibrations that may occur on the island. The observation data from the air vibration gauge and hydrophone, and the data from the GPS wave gauge, were successfully transmitted in real time to a mainland server via satellite transmissions using Thuraya satellites.

Japan has many volcanic islands, and the team aims to use this system to contribute to disaster preparedness and prevention. The system can operate unmanned without refueling, making it suitable for observing faraway islands.

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