Aims, goals and prospects

We have developed the GNSS buoy system for more than 15 years for tsunami early warning. This system was adopted as a national wave monitoring system called The Nationwide Ocean Wave Information Network for Ports and Harbours (NOWPHAS). NOWPHAS established more than 17 GNSS buoy system around the Japanese coasts (Fig. 2). This system enabled to detect tsunamis for the June 2001 Peru earthquake, for the first time [e.g., Kato et al., 2000, 2005] and others. The tsunami due to the March 2011 Tohoku-oki earthquake was detected by a number of the NOWPHAS buoys and was utilized to update the tsunami warning due to the earthquake.

Yet, the conventional GNSS buoys are using the method called RTK-GPS, so that the distance of the buoy from the ground base is limited up to 20km. Therefore, to be more efficient for the tsunami warning, we have tried to improve the system so that the buoy can be established at farther offshore [Terada, 2013]. In these studies, we have implemented a new positioning algorithm called Precise Point Positioning system called PPP-AR, together with satellite data transmission. Some experiments were conducted using this new system with successes [Terada, 2014]. However, we still have some problems to be overcome; for example, data integrity of PPP-AR and reliability of data acquisition. In this research, we are progress the developmental study for better GNSS buoy system, so that PPP-AR is validated for a few centimeters’ accuracy of sea-surface positioning and the integrity of satellite data transmission is much improved by overcoming the problem of degraded communication link between the buoy and the satellite due to the tilting of the buoy.

 Moreover, we are tacking the introduction of GNSS-acoustic method of measuring the sea-floor positioning using the GNSS buoy. The method was first proposed by the US researchers and has been developed by the Japanese researchers. The system was deployed since the beginning of the century and it was able to detect huge crustal movements at the time of the 2011 Tohoku-oki earthquake. However, the system has used vessels for sea-surface positioning. Therefore, repetition interval of measurements has only been several times a year. We are trying to use our GNSS buoy for this purpose as well. If GNSS buoy is used for measuring the ocean floor positioning, nearly continuous positioning of the sea floor would be realized. If such continuous monitoring is realized, the data is more valuable and we would be able to clarify mechanisms of large interplate earthquake, slow slip events that takes place along the plate interface, in more detail.(to be continued)

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Fig. 2 GPS wave meters set around Japanese island as of October 2014 (red circles) and our GNSS buoy (blue square).

History

Contents in preparation

Organization

Teruyuki Kato, The University of Tokyo
Yukihiro Terada, Kochi National College of Technology
Keiichi Tadokoro, Nagoya University
Akira Futamura, National Insititute of Technology, Yuge College
Yoshinori Shoji, Meteorological Research Institute
Mamoru Ishii, National Institute of Information and Communications Technology