TY - JOUR

T1 - Impact of Tropospheric Ties on UT1-UTC in GNSS and VLBI Integrated Solution of Intensive Sessions

AU - Wang, Jungang

AU - Ge, Maorong

AU - Glaser, Susanne

AU - Balidakis, Kyriakos

AU - Heinkelmann, Robert

AU - Schuh, Harald

N1 - Funding information: We would like to thank IGS and IVS for providing observations and products of GNSS and VLBI, IERS for providing EOP products, and TU Wien for providing tropospheric delay products. We would like to thank Dr. James M. Anderson for his support in converting vgosDB into NGSCARD format. We thank the associated editor Dr. Paul Tregoning and the anonymous reviewers for reviewing this manuscript and the insightful comments. Jungang Wang is funded by the Helmholtz OCPC Program (Grant ZD202121). Kyriakos Balidakis is funded by the Deutsche Forschungsgemeinschaft (DFG) Project-ID 434617780 SFB 1464 (TerraQ). Open Access funding enabled and organized by Projekt DEAL. We would like to thank IGS and IVS for providing observations and products of GNSS and VLBI, IERS for providing EOP products, and TU Wien for providing tropospheric delay products. We would like to thank Dr. James M. Anderson for his support in converting vgosDB into NGSCARD format. We thank the associated editor Dr. Paul Tregoning and the anonymous reviewers for reviewing this manuscript and the insightful comments. Jungang Wang is funded by the Helmholtz OCPC Program (Grant ZD202121). Kyriakos Balidakis is funded by the Deutsche Forschungsgemeinschaft (DFG) Project-ID 434617780 SFB 1464 (TerraQ). Open Access funding enabled and organized by Projekt DEAL.

PY - 2022/11/11

Y1 - 2022/11/11

N2 - Very Long Baseline Interferometry (VLBI) intensive (INT) sessions are critical for the rapid determination and densification of Universal Time 1-Coordinate Universal Time (UT1-UTC), which plays an important role in satellite geodesy and space exploration missions and is not predictable over longer time scales. Due to the limited observation geometry of INT sessions with two to three stations observing about 1 hr, tropospheric gradients cannot be estimated, which degrades the UT1-UTC precision. We investigate the impact of tropospheric ties at Global Navigation Satellite Systems (GNSSs) and VLBI co-located stations in INT sessions from 2001 to 2021. VLBI and GNSS observations are combined on the observation level. The results are evaluated by using both UT1-UTC and Length of Day (LOD) from consecutive sessions. We demonstrate a better agreement of 10%–30% when comparing the derived LOD to GNSS LOD for INT1, INT2, and VGOS-2 sessions; whereas, the agreement is not improved when directly comparing UT1-UTC to the IERS Earth Orientation Parameters (EOPs) product, potentially because INT sessions also contribute to IERS EOP products. The major impact comes from tropospheric gradient ties, whereas applying zenith delay ties does not improve or even deteriorate UT1-UTC agreement. Gradient ties also introduce systematic biases in UT1-UTC by around −3 to −5 μs, except for the Russian INT sessions. Regression analysis shows that the east gradient introduces systematic effects in UT1-UTC for sessions involving Germany and USA (Hawaii), whereas for Germany–Japan and Russian sessions, the north gradient also contributes systematically.

AB - Very Long Baseline Interferometry (VLBI) intensive (INT) sessions are critical for the rapid determination and densification of Universal Time 1-Coordinate Universal Time (UT1-UTC), which plays an important role in satellite geodesy and space exploration missions and is not predictable over longer time scales. Due to the limited observation geometry of INT sessions with two to three stations observing about 1 hr, tropospheric gradients cannot be estimated, which degrades the UT1-UTC precision. We investigate the impact of tropospheric ties at Global Navigation Satellite Systems (GNSSs) and VLBI co-located stations in INT sessions from 2001 to 2021. VLBI and GNSS observations are combined on the observation level. The results are evaluated by using both UT1-UTC and Length of Day (LOD) from consecutive sessions. We demonstrate a better agreement of 10%–30% when comparing the derived LOD to GNSS LOD for INT1, INT2, and VGOS-2 sessions; whereas, the agreement is not improved when directly comparing UT1-UTC to the IERS Earth Orientation Parameters (EOPs) product, potentially because INT sessions also contribute to IERS EOP products. The major impact comes from tropospheric gradient ties, whereas applying zenith delay ties does not improve or even deteriorate UT1-UTC agreement. Gradient ties also introduce systematic biases in UT1-UTC by around −3 to −5 μs, except for the Russian INT sessions. Regression analysis shows that the east gradient introduces systematic effects in UT1-UTC for sessions involving Germany and USA (Hawaii), whereas for Germany–Japan and Russian sessions, the north gradient also contributes systematically.

KW - GNSS

KW - integrated processing

KW - intensive sessions

KW - tropospheric ties

KW - UT1-UTC

KW - VLBI

UR - http://www.scopus.com/inward/record.url?scp=85142882751&partnerID=8YFLogxK

U2 - 10.1029/2022JB025228

DO - 10.1029/2022JB025228

M3 - Article

AN - SCOPUS:85142882751

VL - 127

JO - Journal of Geophysical Research: Solid Earth

JF - Journal of Geophysical Research: Solid Earth

SN - 2169-9313

IS - 11

M1 - e2022JB025228

ER -