Assessment of GNSS-based height data of multiple ships for measuring and forecasting great tsunamis

Abstract

Ship height positioning by the Global Navigation Satellite System (GNSS) was investigated for measuring and forecasting great tsunamis. We first examined GNSS height-positioning data of a navigating vessel. If we use the kinematic precise point positioning (PPP) method, tsunamis greater than 10 −1 m will be detected by ship height positioning. Based on Automatic Identification System (AIS) data, we found that tens of cargo ships and tankers are usually identified to navigate over the Nankai Trough, southwest Japan. We assumed that a future Nankai Trough great earthquake tsunami will be observed by the kinematic PPP height positioning of an AIS-derived ship distribution, and examined the tsunami forecast capability of the offshore tsunami measurements based on the PPP-based ship height. A method to estimate the initial tsunami height distribution using offshore tsunami observations was used for forecasting. Tsunami forecast tests were carried out using simulated tsunami data by the PPP-based ship height of 92 cargo ships/ tankers, and by currently operating deep-sea pressure and Global Positioning System (GPS) buoy observations at 71 stations over the Nankai Trough. The forecast capability using the PPP-based height of the 92 ships was shown to be comparable to or better than that using the operating offshore observatories at the 71 stations. We suppose that, immediately after the occurrence of a great earthquake, stations receiving successive ship information (AIS data) along certain areas of the coast would fail to acquire ship data due to strong ground shaking, especially near the epicenter. Such a situation would significantly deteriorate the tsunami-forecast capability using ship data. On the other hand, operational real-time analysis of seismic/geodetic data would be carried out for estimating a tsunamigenic fault model. Incorporating the seismic/geodetic fault model estimation into the tsunami forecast above possibly compensates for the deteriorated forecast capability.

Measuring offshore tsunami currents using ship navigation records

“…Green's functions are composed by tsunami current components in the HDG-normal directions of the respective moving vessel by calculating from unit sources. Referring to our previous study (Inazu et al 2016), we allocate unit sources with the same size/spacing and carry out the inversion/forecast. The inversion/forecast is carried out using the AIS data for 25 min after the earthquake occurrence (Fig.…”

“…A 10 cm tsunami caused by the 2010 Maule, Chile, earthquake was detected by a vertical position change derived from high-precision GPS of a navigating ship (Foster et al 2012). This indicates that navigating ship networks will serve as offshore tsunami observation networks (Inazu et al 2016). However, this requires high-precision GPS facilities on most of the vessels to precisely measure their positions as well as GPS buoys (Terada et al 2015).…”

Preparing for the Future Nankai Trough Tsunami: A Data Assimilation and Inversion Analysis From Various Observational Systems

“…A considerable increase of tsunami observation points is possible with an unconventional way of placing Global Navigation Satellite System (GNSS) receiver on commercial ships (Inazu et al, ). With appropriate corrections, sea surface heights at the ship locations can be precisely measured in real time (Reinking et al, ; Roggenbuck et al, ).…”

“…We apply the proposed algorithms to a possible future scenario of simultaneous occurrence of the Tokai‐Tonankai‐Nankai source earthquakes ( M 8.7) (Central Disaster Management Council, ). The simulated waveforms from this source were obtained from the previous study by Inazu et al (). We consider 163 observation stations, including tsunami data from a possible new way of monitoring sea level by ship height positioning (Inazu et al, ).…”

“…The simulated waveforms from this source were obtained from the previous study by Inazu et al (). We consider 163 observation stations, including tsunami data from a possible new way of monitoring sea level by ship height positioning (Inazu et al, ). However, most of the OBP gauges are located inside the source region, therefore the tsunami waveform is contaminated by the coseismic seafloor deformation (Tsushima et al, ).…”