9:15 AM - 9:30 AM
[SGD01-12] Investigation of angular characteristics of GNSS-A observation acoustic equipment through water tank experiments
Keywords:GNSS-A, SGO-A, Water tank experiment, Acoustic signal reading
The Japan Coast Guard (JCG) has been conducting observations of seafloor crustal deformation using the GNSS-Acoustic ranging combination technique (GNSS-A) for over 20 years. As of February 2024, we deploy the Seafloor Geodetic Observation Array (SGO-A) of 27 seafloor sites, mainly in the Japan Trench and the Nankai Trough.
Compared to GNSS observations, GNSS-A observations lag behind in research to improve observation accuracy in many points. Among the observation errors in GNSS-A, we have been working on the characteristics of the sea surface stations (transducers) and seafloor stations (mirror transponders) in the acoustic ranging. Such equipment-dependent errors are already widely known as antenna offset and Phase Center Variation (PCV) corrections in GNSS observations, and these correction data has also been published.
Regarding the equipment-dependent errors in GNSS-A observations, Honsho et al., (2021) found that a waveform received at a sea-surface station depends on the positional relationship between the two stations (angle from directly below the sea surface station to the seafloor station). The existence of similar angular characteristics in the equipment used by the JCG was confirmed through an experiment conducted in October 2022 at the IIS Ocean Engineering Basin of the University of Tokyo (Nagae et al., JpGU 2023). Through this experiment, we were able to obtain a waveform with less noise that cannot be obtained by actual observation, and Yoshizumi et al., (The Geodetic Society of Japan 2023) used this waveform to reproduce the superposition of acoustic signals and investigated the cause of the distortion.
On the other hand, in this experiment, it was not possible to examine in detail the differences in waveforms depending on the angle, and there were only about five angle variations. Therefore, in February 2024, we conducted a detailed investigation of the angular characteristics using the ultrasonic tank of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). In this experiment, the sound wave sent by a spherical acoustic element are received by three types of transducers: tonpilz, cylindrical, and hemispherical. With rotating the transducer in 5-degree increments, we investigated the characteristics of the received waveform at each angle and instrument. We will report the results obtained from this experiment.
In addition, Nagae et al., (Seismological Society of Japan 2023) investigated a new method for reading acoustic signals at the SGO-A observation sites, and presented a positioning solution at the ASZ1 site on this method. We apply a similar method to multiple observation points, and discuss on the validity of the method.
Compared to GNSS observations, GNSS-A observations lag behind in research to improve observation accuracy in many points. Among the observation errors in GNSS-A, we have been working on the characteristics of the sea surface stations (transducers) and seafloor stations (mirror transponders) in the acoustic ranging. Such equipment-dependent errors are already widely known as antenna offset and Phase Center Variation (PCV) corrections in GNSS observations, and these correction data has also been published.
Regarding the equipment-dependent errors in GNSS-A observations, Honsho et al., (2021) found that a waveform received at a sea-surface station depends on the positional relationship between the two stations (angle from directly below the sea surface station to the seafloor station). The existence of similar angular characteristics in the equipment used by the JCG was confirmed through an experiment conducted in October 2022 at the IIS Ocean Engineering Basin of the University of Tokyo (Nagae et al., JpGU 2023). Through this experiment, we were able to obtain a waveform with less noise that cannot be obtained by actual observation, and Yoshizumi et al., (The Geodetic Society of Japan 2023) used this waveform to reproduce the superposition of acoustic signals and investigated the cause of the distortion.
On the other hand, in this experiment, it was not possible to examine in detail the differences in waveforms depending on the angle, and there were only about five angle variations. Therefore, in February 2024, we conducted a detailed investigation of the angular characteristics using the ultrasonic tank of Japan Agency for Marine-Earth Science and Technology (JAMSTEC). In this experiment, the sound wave sent by a spherical acoustic element are received by three types of transducers: tonpilz, cylindrical, and hemispherical. With rotating the transducer in 5-degree increments, we investigated the characteristics of the received waveform at each angle and instrument. We will report the results obtained from this experiment.
In addition, Nagae et al., (Seismological Society of Japan 2023) investigated a new method for reading acoustic signals at the SGO-A observation sites, and presented a positioning solution at the ASZ1 site on this method. We apply a similar method to multiple observation points, and discuss on the validity of the method.