GNSS-Acoustic Observations of Seafloor Crustal Deformation Using a Wave Glider

Takeshi Iinuma,Motoyuki Kido,Tatsuya Fukuda,Iwao Ueki,Fumiaki Tomita,Yusaku Ohta

doi:10.3389/feart.2021.600946

Takeshi Iinuma, Motoyuki Kido + Show 4 more

Open Access

https://doi.org/10.3389/feart.2021.600946

Copy DOI

Abstract

Crustal deformation of the seafloor is difficult to observe solely using global navigation satellite system (GNSS). The GNSS-acoustic (GNSS-A) technique was developed to observe seafloor crustal deformation, and it has produced a steady series of successful observations with remarkable results related to crustal deformation associated with huge earthquakes around the Japanese Islands. However, utilizing GNSS-A incurs very large financial and human costs as it requires the use of a research vessel as a surface platform and has a limited observation frequency, which is less than once a year at seafloor stations along the Japan Trench. To conduct frequent observations, an automatic GNSS-A data acquisition system was developed that operates via an unmanned surface vehicle (wave glider). The first observations using this system were performed at a seafloor station off Aomori Prefecture in July 2019. The wave glider was equipped with two GNSS antennas, an acoustic transducer, a microelectromechanical system gyroscope, and associated control and logging units. Data acquisition and autonomous activation of the seafloor stations were successfully executed by controlling the power supply to the payload via satellite communication with the wave glider. The glider rarely strayed off the configured course and the solar panels generated sufficient power to perform the observations although the weather was mostly cloudy. The GNSS-A data processing results show that the position of the station was determined with the same accuracy and precision as in previous observations performed using a research vessel.

Highlights

While terrestrial crustal deformation has been monitored using global navigation satellite system (GNSS) observations since the 1990s, crustal deformation of submarine offshore regions is difficult to detect using satellite geodetic methods as the electromagnetic waves cannot penetrate the deep ocean to reach the seafloor
To conduct frequent observations and ensure easy maintenance, we have developed an automatic GNSS-A data acquisition system using a wave glider (WG), which is an unmanned surface vehicle
We report on the developed GNSS-A system installed in the WG, initial sea trial conducted in July 2019, and results of data processing from the trial deployment of the WG

Summary

Introduction

While terrestrial crustal deformation has been monitored using global navigation satellite system (GNSS) observations since the 1990s, crustal deformation of submarine offshore regions is difficult to detect using satellite geodetic methods as the electromagnetic waves cannot penetrate the deep ocean to reach the seafloor. The GNSS-acoustic (GNSS-A) technique was developed to overcome this difficulty in observing seafloor crustal deformation (Spiess, 1985; Spiess et al, 1998; Asada and Yabuki, 2001; Fujita et al, 2006). Conventional GNSS-A requires large financial and human costs because a research vessel that functions as a surface platform is exclusively necessary. Tohoku University installed 20 seafloor GNSS-A stations in 2012 following the 2011 Tohoku-oki earthquake to detect post-seismic deformation due to the earthquake (Kido et al, 2015). Repeated observations at all stations have not been conducted frequently (i.e., less than once a year), especially after 2017 due to financial difficulties as usage of a research vessel costs several tens of thousands of dollars per day (cf Tomita et al, 2017)

Methods

Results

Conclusion