12:00 PM - 12:15 PM
[SGD03-12] Time series data of SGO-A sites
Keywords:GNSS-A, SGO-A, Positioning Solution
Hydrographic and Oceanographic Department, Japan Coast Guard has been routinely conducting seafloor geodetic observations using the GNSS-acoustic technique (GNSS-A) for over 20 years. GNSS-A observation involves determining the position of a mirror transponder (seafloor station) by measuring the distance from the sea-surface platform (sea station; like a survey vessel) to the mirror transponder (sea-floor station). As of February 2025, JCG has deployed a GNSS-A observation network called SGO-A (Seafloor Geodetic Observation Array) at a total of 27 sites, mainly along the Nankai Trough and Japan Trench.
GNSS-A observations can measure the position of the seafloor station with centimeter-level accuracy. To further improve, we have been investigating instrument bias, which is thought to be one of the major sources of observation error in current observations. For example, Yokota et al. (2024, EPS) and Nagae et al. (2024, Ultrasonic Research Society) investigated differences in received waveforms for each acoustic device using a water tank, as well as differences in waveforms depending on the take-off angle between the sea-surface station and the seafloor station, and reported that the characteristics obtained in actual observations were confirmed also in experiment.
In our routine analysis, the transmission and receive times of acoustic signals are calculated using the method proposed by Tomiyama (2003, Technical bulletin on hydrography and oceanography). However, this method "checks the height of the peaks in sequence, and adopts the position of the peak whose amplitude ratio with the next peak falls below a threshold as the receive time," and it does not take into account differences the take-off angle.
Therefore, we developed a new method for the acoustic signal reading, the AAR method (Yokota et al., 2024, EPS). In this method, the receive waveform is stacked for each take-off angle to create a template waveform, and the reading position is corrected based on the round-trip traveltime residual obtained from the analysis of the positioning solution by the GARPOS (Watanabe et al., 2020, FES) software. This makes it possible to calculate more accurate positioning solutions.
In this presentation, we discuss the time variation in the positioning solutions for the SGO-A site using the AAR method.
GNSS-A observations can measure the position of the seafloor station with centimeter-level accuracy. To further improve, we have been investigating instrument bias, which is thought to be one of the major sources of observation error in current observations. For example, Yokota et al. (2024, EPS) and Nagae et al. (2024, Ultrasonic Research Society) investigated differences in received waveforms for each acoustic device using a water tank, as well as differences in waveforms depending on the take-off angle between the sea-surface station and the seafloor station, and reported that the characteristics obtained in actual observations were confirmed also in experiment.
In our routine analysis, the transmission and receive times of acoustic signals are calculated using the method proposed by Tomiyama (2003, Technical bulletin on hydrography and oceanography). However, this method "checks the height of the peaks in sequence, and adopts the position of the peak whose amplitude ratio with the next peak falls below a threshold as the receive time," and it does not take into account differences the take-off angle.
Therefore, we developed a new method for the acoustic signal reading, the AAR method (Yokota et al., 2024, EPS). In this method, the receive waveform is stacked for each take-off angle to create a template waveform, and the reading position is corrected based on the round-trip traveltime residual obtained from the analysis of the positioning solution by the GARPOS (Watanabe et al., 2020, FES) software. This makes it possible to calculate more accurate positioning solutions.
In this presentation, we discuss the time variation in the positioning solutions for the SGO-A site using the AAR method.