5:15 PM - 6:45 PM
[SGD01-P08] Evaluation of systematic differences between VLBI and GNSS at Ishioka Geodetic Observing Station
Keywords:VLBI, Local tie vector
Introduction
International Terrestrial Reference Frame (ITRF) is established with four space geodetic techniques: VLBI, GNSS, SLR and DORIS. To combine each observation networks, local tie vectors between each observation station are important information at sites that operate multiple space geodetic techniques.
The Geospatial Information Authority of Japan (GSI) operates observation facilities of VLBI and GNSS at the Ishioka Geodetic Observing station. GSI conducts local tie survey between VLBI antenna and GNSS Continuously Operating Reference Station (CORS) once a year and submits the result to International Earth Rotation and Reference Systems Service (IERS) (Matsumoto, et al., 2022).
VLBI antenna at the Ishioka Geodetic Observing station (hereafter “Ishioka VLBI antenna”) had participated in over 530 observations since 2015 as of November 13, 2023. In this study, we calculated the position of Ishioka VLBI antenna using these accumulated data. We also tried to evaluate the systematic difference between VLBI and GNSS by comparison of their positions using the local tie vector.
In this presentation, we will report the estimated position of Ishioka VLBI antenna and the results of comparison with the position of GNSS CORS “ISHI”.
Calculation of position of Ishioka VLBI antenna
In this study, we estimated the position of Ishioka VLBI antenna as of January 1, 2024. The software we used is CALC (Ver.11) / SOLVE (release 2023.1.15, revision 2023.2.16). we also used ITRF2020 (Altamimi, et al., 2022) as a priori positions of stations.
There are two ways to calculate position of VLBI antenna. The first is to calculate position for each observation (hereafter “Analysis for each session”) and the second is to estimate position by analyzing all observations (hereafter “Global analysis”). In the Analysis for each session, it is not able to obtain daily position because observations for geodetic purpose are not conducted every day. And position for each session can be different from the average because positions obtained from the Analysis for each session tend to have large variations. So, we estimated the position of Ishioka VLBI antenna by non-linear fitting with time series of the positions obtained from the Analysis for each session with data of all 24 hours observations.
In the Global analysis, the software can estimate position and velocity of station, but it cannot estimate displacement with earthquake and post seismic deformation. Generally, post seismic deformation models (hereafter “PSD models”) are described in ITRF2020 and we use them as known parameters in analysis. Ishioka VLBI antenna is affected by post seismic deformation after the 2011 off the Pacific coast of Tohoku Earthquake. However, the PSD model at Ishioka VLBI antenna is not described in ITRF2020 because the antenna did not exist as of 2011. It is an issue that the velocity at Ishioka VLBI antenna obtained from the Global analysis contains effect of post seismic deformation and it can be an error factor. So, in the Global analysis, we analyzed all observation data using PSD model defined by fitting functions obtained from the Analysis for each session and estimated position of Ishioka VLBI antenna as of January 1, 2024.
Estimated position of VLBI antenna and comparison of positions of VLBI and GNSS
In the result of the Analysis for each session, there are variation of several mm between positions of each session (Fig. 1). The position and the velocity obtained from the Global analysis are consistent with the results of the Analysis for each session (Fig.2).
We also compared the estimated positions of Ishioka VLBI antenna with F5 solutions of GNSS CORS “ISHI” using local tie vector between those observation points. As the result, trend of displacement of Ishioka VLBI antenna since 2015 is consistent with F5 solutions of “ISHI”. On the other hand, there are systematic differences less than 1 cm between them (Fig.3).
International Terrestrial Reference Frame (ITRF) is established with four space geodetic techniques: VLBI, GNSS, SLR and DORIS. To combine each observation networks, local tie vectors between each observation station are important information at sites that operate multiple space geodetic techniques.
The Geospatial Information Authority of Japan (GSI) operates observation facilities of VLBI and GNSS at the Ishioka Geodetic Observing station. GSI conducts local tie survey between VLBI antenna and GNSS Continuously Operating Reference Station (CORS) once a year and submits the result to International Earth Rotation and Reference Systems Service (IERS) (Matsumoto, et al., 2022).
VLBI antenna at the Ishioka Geodetic Observing station (hereafter “Ishioka VLBI antenna”) had participated in over 530 observations since 2015 as of November 13, 2023. In this study, we calculated the position of Ishioka VLBI antenna using these accumulated data. We also tried to evaluate the systematic difference between VLBI and GNSS by comparison of their positions using the local tie vector.
In this presentation, we will report the estimated position of Ishioka VLBI antenna and the results of comparison with the position of GNSS CORS “ISHI”.
Calculation of position of Ishioka VLBI antenna
In this study, we estimated the position of Ishioka VLBI antenna as of January 1, 2024. The software we used is CALC (Ver.11) / SOLVE (release 2023.1.15, revision 2023.2.16). we also used ITRF2020 (Altamimi, et al., 2022) as a priori positions of stations.
There are two ways to calculate position of VLBI antenna. The first is to calculate position for each observation (hereafter “Analysis for each session”) and the second is to estimate position by analyzing all observations (hereafter “Global analysis”). In the Analysis for each session, it is not able to obtain daily position because observations for geodetic purpose are not conducted every day. And position for each session can be different from the average because positions obtained from the Analysis for each session tend to have large variations. So, we estimated the position of Ishioka VLBI antenna by non-linear fitting with time series of the positions obtained from the Analysis for each session with data of all 24 hours observations.
In the Global analysis, the software can estimate position and velocity of station, but it cannot estimate displacement with earthquake and post seismic deformation. Generally, post seismic deformation models (hereafter “PSD models”) are described in ITRF2020 and we use them as known parameters in analysis. Ishioka VLBI antenna is affected by post seismic deformation after the 2011 off the Pacific coast of Tohoku Earthquake. However, the PSD model at Ishioka VLBI antenna is not described in ITRF2020 because the antenna did not exist as of 2011. It is an issue that the velocity at Ishioka VLBI antenna obtained from the Global analysis contains effect of post seismic deformation and it can be an error factor. So, in the Global analysis, we analyzed all observation data using PSD model defined by fitting functions obtained from the Analysis for each session and estimated position of Ishioka VLBI antenna as of January 1, 2024.
Estimated position of VLBI antenna and comparison of positions of VLBI and GNSS
In the result of the Analysis for each session, there are variation of several mm between positions of each session (Fig. 1). The position and the velocity obtained from the Global analysis are consistent with the results of the Analysis for each session (Fig.2).
We also compared the estimated positions of Ishioka VLBI antenna with F5 solutions of GNSS CORS “ISHI” using local tie vector between those observation points. As the result, trend of displacement of Ishioka VLBI antenna since 2015 is consistent with F5 solutions of “ISHI”. On the other hand, there are systematic differences less than 1 cm between them (Fig.3).