5:15 PM - 7:15 PM
[SGD02-P08] Accuracy Evaluation of Daily Coordinates of GEONET CORS aligned with ITRF2020
Keywords:GNSS, GEONET, F5
Geospatial Information Authority of Japan (GSI) has been operating GEONET (GNSS Earth Observation Network System), a GNSS continuous observation network covering the entire country, since 1996. GEONET, which initially started operation with 610 stations, consists of approximately 1,300 stations. Daily coordinates of GNSS CORS (Continuously Operating Reference Stations), which are analyzed in accordance with a consistent analysis strategy for the entire period, are widely used as basic data in research area of geodesy and geophysics, as well as for management of the national geodetic reference frame including crustal deformation monitoring. In recent years, they have also been used as the infrastructure for location-based services, for example CLAS, the high-precision positioning service of the Quasi-Zenith Satellite System in Japan. The current analysis strategy (5th edition), which aligns to ITRF2014 as the reference coordinate system, consists of two steps: a fixed-point analysis to obtain the coordinates of a GEONET station ‘TSUKUBA1’ on the GSI's premises utilizing global observation data, and a nationwide analysis to obtain the coordinates of the other stations covering entire country with respect to ‘TSUKUBA1’ station. The daily coordinates based on the strategy are called ‘F5 solutions’ (Takamatsu et al., 2023; Muramatsu et al., 2021) , which have been available since April 2021.
Based on the publication of ITRF2020 in 2022 and its updated version, ITRF2020-u2023, where definition is identical to ITRF2020, in December 2024, the GSI is evaluating impact on daily coordinates due to the change of reference coordinate system from ITRF2014 to ITRF2020. In this study, along with the change of reference coordinate system from ITRF2014 to ITRF2020, the IGS final precise ephemeris is used for the satellite orbit, and the initial coordinates for the analysis are given by the IGS20 realization with post-seismic deformation. Concerning the antenna phase center correction, basically the IGS model is employed for the fixed-point analysis while the GSI original model is applied for the nationwide analysis. To ensure alignment to ITRF2020, the latter model is newly constructed independently based on the observation results from the antenna test pillar at GSI (see Toyofuku et al., 2009, for the procedure). Except for these changes, the other settings are the same as current analysis.
The figure shows the time series of the F5 solution and the new analysis result aligned with ITRF2020 (named F5.1 solution here for the sake of convenience) for the TSUKUBA1 site from January 2023 to December 2024. It can be seen that the F5 solution shows a slight increase in the dispersion of the east-west and north-south components in the last one to two years, while the dispersion of the F5.1 solution is relatively suppressed. In the vertical component, there is an apparent reversal of velocity between the F5 and F5.1 solutions after 2024, although this is an initial evaluation over a limited period. The absolute value of difference in two time series deviates by about 1 cm in the horizontal component although the impact of the systematic difference between the ITRF2014 and ITRF2020 definitions is considered at most 2 to 3 mm according to the conversion parameters between them. The result of this evaluation shows slightly larger discrepancy than expectation from difference of reference frame. A presumed cause of those differences is the increase of the available stations in ITRF2020 taking into account the discontinuous events after the release of ITRF2014. We will continue to evaluate the accuracy of daily coordinates with the latest reference frame, including nationwide analysis.
Based on the publication of ITRF2020 in 2022 and its updated version, ITRF2020-u2023, where definition is identical to ITRF2020, in December 2024, the GSI is evaluating impact on daily coordinates due to the change of reference coordinate system from ITRF2014 to ITRF2020. In this study, along with the change of reference coordinate system from ITRF2014 to ITRF2020, the IGS final precise ephemeris is used for the satellite orbit, and the initial coordinates for the analysis are given by the IGS20 realization with post-seismic deformation. Concerning the antenna phase center correction, basically the IGS model is employed for the fixed-point analysis while the GSI original model is applied for the nationwide analysis. To ensure alignment to ITRF2020, the latter model is newly constructed independently based on the observation results from the antenna test pillar at GSI (see Toyofuku et al., 2009, for the procedure). Except for these changes, the other settings are the same as current analysis.
The figure shows the time series of the F5 solution and the new analysis result aligned with ITRF2020 (named F5.1 solution here for the sake of convenience) for the TSUKUBA1 site from January 2023 to December 2024. It can be seen that the F5 solution shows a slight increase in the dispersion of the east-west and north-south components in the last one to two years, while the dispersion of the F5.1 solution is relatively suppressed. In the vertical component, there is an apparent reversal of velocity between the F5 and F5.1 solutions after 2024, although this is an initial evaluation over a limited period. The absolute value of difference in two time series deviates by about 1 cm in the horizontal component although the impact of the systematic difference between the ITRF2014 and ITRF2020 definitions is considered at most 2 to 3 mm according to the conversion parameters between them. The result of this evaluation shows slightly larger discrepancy than expectation from difference of reference frame. A presumed cause of those differences is the increase of the available stations in ITRF2020 taking into account the discontinuous events after the release of ITRF2014. We will continue to evaluate the accuracy of daily coordinates with the latest reference frame, including nationwide analysis.