Development of GNSS Buoy for a Synthetic Geohazard Monitoring System

Abstract

The GNSS buoy system for early tsunami warnings has been under development for about 20 years. A small prototype buoy was first deployed in Sagami Bay, Japan, in 1997. Then, after a series of experiments aiming for operational use, the system was implemented as a part of national wave monitoring system NOWPHAS. The NOWPHAS system had set up more than 10 GNSS buoys around Japan by 2011, and it recorded the tsunami caused by the 11 March 2011 Tohoku-oki earthquake. The records were used to update the tsunami warning at the time of the 2011 Tohoku-oki earthquake. However, the buoys were placed less than 20 km from the coast, as the system used the baseline mode RTK-GPS algorithm, which was not far enough for effective evacuation of people. Thus, we began trying to improve the system by putting the buoys much farther from the coast. The new system employs a newly developed positioning algorithm, Precise Point Positioning with Ambiguity Resolution (PPP-AR), together with satellite data transmission. A series of experiments involving the new system successfully indicated changes in sea level with an accuracy of a few centimeters. Given the success of the experiments, we are trying to use the GNSS buoys not only to provide early tsunami warnings but also to monitor various other geohazards. For example, we are trying to use the GNSS-Acoustic system to continuously monitor crustal movements on the ocean floor, to monitor the ionosphere, and to monitor the atmosphere. Ancillary sensors on the buoys will be utilized for oceanographic monitoring as well.

History of on-board equipment improvement for GNSS-A observation with focus on observation frequency

“…Therefore, increasing the observation frequency of affected sites is essential, and the development of a new sea surface platform rather than a vessel is required. There are already studies on a GNSS buoy (Takahashi et al, 2014;Kato et al, 2018)and an automated vehicle (Chadwell, 2016), but the feasibility of such a system needs to be examined, considering both operation safety and costs. Also, examination of various possibilities in sea surface platform engineering will continue to be essential.…”

“…The ideal solution to improve the temporal resolution of the GNSS-A is continuous observation using an unmanned sea surface platform instead of a vessel. An unmanned sea surface platform has been developed by some research groups (Takahashi et al, 2014;Kato et al, 2018), but it has not yet been put into use for stable observation. It is therefore now important to develop a technology that increases the frequency of vessel-based observation, which is limited by the high costs associated with using a ship, including vessel operation time.…”

Development of a kinematic GNSS-Acoustic positioning method based on a state-space model

“…Furthermore, the EKF-based positioning method can provide kinematic solutions instantly, just after collection of the acoustic ranging data for each ping, because this technique does not need "future" acoustic ranging data to constrain the temporal variation in NTDs. Recently, some trials of real-time and continuous GNSS-A observations have been conducted using a moored buoy (e.g., Imano et al 2015;Kido et al 2018;Kato et al 2018;Tadokoro et al 2018a). In this application, kinematic GNSS-A positions are estimated using a small computer attached to the buoy, which are then transmitted to an onshore station via satellite relay.…”

“…Although GNSS-A observations are typically collected by campaign-style surveys using a research vessel as the sea surface platform, continuous GNSS-A observations have recently been developed using moored buoys (e.g., Imano et al 2015;Kido et al 2018;Kato et al 2018;Imano et al 2019) for an early warning system through instant offshore geodetic positioning. To support these efforts, we investigate a precise "kinematic" GNSS-A positioning method.…”

Assessment of directional accuracy of GNSS-Acoustic measurement using a slackly moored buoy

“…Moored Global Positioning System (GPS) buoys have been developed to monitor wave heights and tsunamis using real-time kinematic GPS positioning (Kato et al 2000;2011;Terada et al 2015) or an on-site real-time precise point positioning (PPP, Zumberge et al 1997) technique (Terada et al 2013) along the Pacific coast of Japan. Kato et al (2018) implemented a GNSS-A system for one of the moored buoys and began experimental measurements. Takahashi et al (2014) developed a mooring system for seafloor crustal movement and tsunami monitoring and conducted a 3-month sea trial in 2013, 100 km from the Kii Peninsula, at a depth of 3000 m. This mooring system was a prototype for our research.…”