The Land, Infrastructure, Transport and Tourism Ministry in Japan has decided to introduce a system to transmit data from 15 wave gauges equipped with the Global Positioning System (GPS) off Japan’s shores to ground stations via a private-sector communications satellite by the end of this fiscal year.
The ministry estimates the cost of building the satellite system will be about 100 million yen
After last year’s Great East Japan Earthquake, reported the Yomiuri Shimbun, ground telecommunications networks for this purpose were severed by tsunami or power blackouts. Taking a lesson from that experience, the ministry aims to make the data transmission networks dual-structured, using both ground and satellite communications.
Also, to prepare for tsunami following a predicted huge earthquake with an epicentre along the Nankai Trough, the ministry will deploy three more wave gauges in the Pacific Ocean off western Japan and significantly strengthen monitoring.
Currently, data from the wave gauges are transmitted to ground receiving stations in coastal areas and then sent via dedicated lines to the ministry’s port offices.
The data is then sent to the Port and Airport Research Institute in Yokosuka, Kanagawa Prefecture, which finally stores the data.
In the disaster in March last year, three wave gauges off the Tohoku region transmitted direct measurements of the first waves of tsunami. This information contributed to the Japan Meteorological Agency raising the predicted heights of the tsunami. But when the tsunami reached the shore, ground telecommunications lines were severed in the ensuing destruction.
As power blackouts occurred in tsunami-hit areas, the system could not be used to observe changes on the sea surface and issue or lift warnings or cautions about tsunami afterward.
Though it is predicted that a wide range of areas will be damaged by tsunami if the Nankai Trough quake occurs, simply reinforcing the ground facilities against tsunami or blackouts will have a limited effect.
The ministry wants to strengthen the fragile telecommunication networks quickly, and plans to build a new system that can transmit a large volume of information from the wave gauges directly to the institute via a communication satellite with a large data transmission capability.
The ministry aims to supplement the telecommunications network, which so far has operated only with ground facilities.The ministry estimates the cost of building the satellite system will be about 100 million yen.
The satellite to be used for the system will be selected by bidding and will have to meet certain criteria, such as being able to cover the entire nation. Wave gauges are currently in place in 12 locations in the Pacific Ocean and three in the Sea of Japan.
The GPS wave gauges are buoys floating on the sea about 20 kilometers from shore, where the height of tsunami waves tends to become rapidly higher. Using signals from GPS satellites, the devices can measure upward and downward movements of the sea surface, recognising only a few centimetres of difference.
In the Great East Japan Earthquake, the wave gauges observed surges of up to 6.7 meters caused by tsunami about 10 minutes before the waves reached the shore.