3:45 PM - 4:00 PM
[SCG52-02] Development of an ultralight and compact towed buoy system for GNSS/A seafloor geodesy.
Keywords:GNSS/A geodesy, Seafloor crustal deformation, Towed Buoy
We are developing an ultra-lightweight and compact towed-buoy system for GNSS/A geodetic measurement.
For GNSS/A geodesy, it is important to achieve high accuracy in positioning within a short measurement time. Ishikawa et al. (2020) showed that a system which can cover a wide area in a short time and trace well-controlled ship tracks is effective for this purpose. To achieve this, they developed a hull-mounted system that can transmit and receive acoustic signals with a high S/N ratio while sailing at high speeds (~7 knots) (Sato et al., 2013). However, this system requires a dedicated observation vessel equipped with a transducer on the bottom of it and a very expensive gyrocompass. Research groups without their own vessels that wish to conduct observations on a low budget would appreciate a portable system that can be adapted to any rental vessel.
Therefore, we have been developing an ultra-lightweight, small-sized and high-speed towed buoy system that can be transported and handled by small vessels. Tohoku University (Funakoshi et al. 2006) and a group in Taiwan (Chen et al. 2021) have also developed buoys that are 1.5 m and 2.5 m in length, weigh 250 kg and 150 kg, respectively, and can be handled manually. However, it is not practical to drop and pick up these buoys without an A-frame or crane, and on-land transportation is also very hard. Also, the maximum speed of these buoys is only about 2 knots, which is not very high.
Then, we designed a buoy weighing about 25 kg that can be handled by two persons on board of a ship and towed at a speed close to 7 knots. We complete it conducting a series of experiments in a 50-m pool at Shizuoka University.
The completed buoy is a laterally flattened shape with 1.5 m in length and 30 cm in thickness, made of a polyurethane foam coated with FRP, 1.5 m in height including the transducer pole, and 25 kg in weight. In the towing experiment, the buoy can run at a maximum speed of 5 knots (which was the limit of human power). In February and March, we will conduct a towing experiment in Suruga Bay using Tokai University's vessel Hokuto. The S-N ratio of acoustic signal will be checked while the vessel is being towed, and then we adopt it in actual measurement in off-Nansei Islands.
Acknowledgement:
This work was supported by JSPS KAKENHI Grant Number22H01335.
Reference:
Chen et al. (2021). A Decade of Global Navigation Satellite System/Acoustic Measurements of Back-Arc Spreading in the Southwestern Okinawa Trough. Front. Earth Sci. 9:601138. doi: 10.3389/feart.2021.601138.
Funakoshi et al. (2006). Initial Results of GPS/Acoustic Seaf loor Positioning using a Small Towed Buoy off Miyagi Prefecture, Northeastern Japan, Journal of the Geodetic Society of Japan, 52, No.2, pp.115-130.
Ishikawa et al. (2020). History of on-board equipment improvement for GNSS-A observation with focus on observation frequency. Front. Earth Sci. 8:150. doi: 10.3389/feart.2020.00150.
Sato et al. (2013). Interplatecoupling off northeastern Japan before the 2011 Tohoku-oki earthquake, inferred from seafloor geodetic data,J. Geophys.Res. Solid Earth,118, 3860–3869, doi:10.1002/jgrb.50275.
For GNSS/A geodesy, it is important to achieve high accuracy in positioning within a short measurement time. Ishikawa et al. (2020) showed that a system which can cover a wide area in a short time and trace well-controlled ship tracks is effective for this purpose. To achieve this, they developed a hull-mounted system that can transmit and receive acoustic signals with a high S/N ratio while sailing at high speeds (~7 knots) (Sato et al., 2013). However, this system requires a dedicated observation vessel equipped with a transducer on the bottom of it and a very expensive gyrocompass. Research groups without their own vessels that wish to conduct observations on a low budget would appreciate a portable system that can be adapted to any rental vessel.
Therefore, we have been developing an ultra-lightweight, small-sized and high-speed towed buoy system that can be transported and handled by small vessels. Tohoku University (Funakoshi et al. 2006) and a group in Taiwan (Chen et al. 2021) have also developed buoys that are 1.5 m and 2.5 m in length, weigh 250 kg and 150 kg, respectively, and can be handled manually. However, it is not practical to drop and pick up these buoys without an A-frame or crane, and on-land transportation is also very hard. Also, the maximum speed of these buoys is only about 2 knots, which is not very high.
Then, we designed a buoy weighing about 25 kg that can be handled by two persons on board of a ship and towed at a speed close to 7 knots. We complete it conducting a series of experiments in a 50-m pool at Shizuoka University.
The completed buoy is a laterally flattened shape with 1.5 m in length and 30 cm in thickness, made of a polyurethane foam coated with FRP, 1.5 m in height including the transducer pole, and 25 kg in weight. In the towing experiment, the buoy can run at a maximum speed of 5 knots (which was the limit of human power). In February and March, we will conduct a towing experiment in Suruga Bay using Tokai University's vessel Hokuto. The S-N ratio of acoustic signal will be checked while the vessel is being towed, and then we adopt it in actual measurement in off-Nansei Islands.
Acknowledgement:
This work was supported by JSPS KAKENHI Grant Number22H01335.
Reference:
Chen et al. (2021). A Decade of Global Navigation Satellite System/Acoustic Measurements of Back-Arc Spreading in the Southwestern Okinawa Trough. Front. Earth Sci. 9:601138. doi: 10.3389/feart.2021.601138.
Funakoshi et al. (2006). Initial Results of GPS/Acoustic Seaf loor Positioning using a Small Towed Buoy off Miyagi Prefecture, Northeastern Japan, Journal of the Geodetic Society of Japan, 52, No.2, pp.115-130.
Ishikawa et al. (2020). History of on-board equipment improvement for GNSS-A observation with focus on observation frequency. Front. Earth Sci. 8:150. doi: 10.3389/feart.2020.00150.
Sato et al. (2013). Interplatecoupling off northeastern Japan before the 2011 Tohoku-oki earthquake, inferred from seafloor geodetic data,J. Geophys.Res. Solid Earth,118, 3860–3869, doi:10.1002/jgrb.50275.