Engineering news
Japanese researchers have tested an island volcano monitoring system in the seas around Nishinoshima, where eruptions have been continuing since November 2013.
The monitoring system uses a wave glider that can operate autonomously relying solely on wave power, without refueling. It is equipped with cameras for visual observation of the volcano, a GPS wave gauge that can detect tsunami caused by volcanic collapse, and a gauge that checks for earthquakes and air vibrations by measuring sonic waves in the air and water.
The collaborative research team 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 were successfully tested these features during a test run around the island.
In order to monitor the system in real time, they continuously transmitted data from the wave gauge and earthquake/air tremor gauge to a server on the mainland 1000km from Nishinoshima using satellite transmissions.
The research team began development of the project when Nishinoshima was still very active. They boarded a ship and took video footage, air vibration measurements, volcanic activity measurements using hydrophones, and carried out a transmission test using the satellite communications system, 7km from the crater for two days.
Based on the above tests, they developed sensor equipment for the island volcano monitoring system and attached it to a wave glider.
The wave glider used for this system consists of a float above water connected by a 5.8m umbilical cable to an underwater glider that propels the wave glider. As well as being equipped with the necessary controllers for the wave glider, 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, detecting 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 Nishinoshima by taking 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.
However, there are constraints on the speed and safety of satellite transmissions for sending data in real time, and limits on the amount of electricity that can be used by this system.
Until recently, observation of the volcano was mainly carried out by artificial satellites and a monthly aircraft visit by the Japan Coast Guard. The group now plans to start preparing the system for practical use to contribute to disaster preparedness and prevention.