Local-tie Experiments of Chinese VLBI Stations

Local-tie Experiments of Chinese VLBI Stations Xuan He1, Fengchu Shu1, Minghui Xu2, Yidan Huang1, Jiangying Gan1, Bo Xia1, Cong Liu1 1Shanghai Astronomical Observatory, Chinese Academy of Sciences 2GFZ Helmholtz Centre for Geosciences [email protected] Abstract This report presents local-tie experiments using three co-located VLBI stations in China: Tianma and Sheshan in Shanghai, and Urumqi. The VGOS antennas were utilized in mixed-mode observations across the conventional S/X bands, followed by correlation of X-band-only data and subsequent post-correlation analysis. Phase delay analysis was performed to determine the relative coordinates of these co-located VLBI antennas. Moreover, TIANMA13 and SESHAN13, forming a baseline of 6km long, joined a few VGOS 24-h sessions together. We attempted to determine the baseline vector using phase delay approach. Experiments TIANMA13-TIANMA65 ~179m SESHAN25-SESHAN13 ~55m URUMQI-URUMQI13 ~374m Data for Phase Delay Research: • S/X Mixed-mode Tag-along Experiments: 7 sessions (Legacy + VGOS stations; X-band only) • IVS VGOS-OPS Experiment: 1 session (Shanghai VGOS stations; B&C bands; Only Y-polarization was employed) Session Time Stations Session Time Stations AOV056 2021-02-03 ShS6 RD2303 2023-04-12 T6T1 AOV057 2021-03-22 ShS6 AOV082 2023-04-26 T6T1 AOV058 2021-04-27 T6T1 APSG53 2023-08-30 UrUm AOV062 2021-08-24 ShS6 VO5148 2025-05-28 S6T1 Data Processing - Mixed-Mode Data Processing - VGOS Mode • Phase delay solutions (blue) yield superior precision, with smaller WRMS delay residuals and baseline vector formal errors than group delay solutions (black) • Phase delay solutions from Tianma stations show better repeatability across sessions Future Plans • Investigate why the phase delay solutions in AOV057/AOV062 were failed. • Perform more dedicated local-tie experiments. • Process all SESHAN13-TIANNA13 VGOS data using the pipeline developed in VO5148, considering polarization combination method. Site Session WRMS /ps Obs Used Length /mm X Comp /mm Y Comp /mm Z Comp /mm Sheshan AOV056 9.3 417 55511.7 ± 0.4 -40597.8 ± 0.8 3903.6 ± 1.2 -37658.1 ± 0.8 20.4 419 55507.5 ± 1.0 -40585.7 ± 1.7 3903.1 ± 2.6 -37665.0 ± 1.7 Tianma AOV058 4.2 88 178526.5 ± 0.5 93064.1 ± 0.8 -17027.1 ± 1.2 151396.4 ± 0.8 34.3 67 178537.6 ± 4.8 93053.4 ± 8.3 -17007.0 ± 11.6 151418.4 ± 7.8 RD2303 6.7 117 178529.1 ± 1.2 93063.7 ± 1.0 -17022.0 ± 1.6 151400.3 ± 1.5 18.5 117 178533.3 ± 3.2 93058.6 ± 2.7 -17013.0 ± 4.4 151409.4 ± 4.0 AOV082 6.9 216 178527.9 ± 0.5 93065.5 ± 0.7 -17027.8 ± 1.0 151397.1 ± 0.7 11.2 218 178528.1 ± 0.8 93045.7 ± 1.1 -17000.4 ± 1.7 151412.6 ± 1.3 Urumqi APSG53 7.1 403 373621.9 ± 0.2 -361562.5 ± 0.2 66934.9 ± 0.8 -66224.1 ± 0.7 15.5 413 373621.7 ± 0.5 -361562.0 ± 0.6 66932.2 ± 1.7 -66228.3 ± 1.5 Sheshan -Tianma VO5148 14.4 516 6051321.2 ± 0.5 4845144.5 ± 1.1 3524517.6 ± 1.5 -849021.9 ± 1.2 17.7 520 6051323.4 ± 0.5 4845148.7 ± 1.3 3524514.6 ± 2.0 -849026.0 ± 1.4 VLBI co-located antennas in China, located in Shanghai ( Sheshan and Tianma ) and Urumqi. 10th IVTW 21-25 Oct 2025 Chalmers, Gothenburg Result & Analysis Preliminary Phase-Delay Processing for Pure VGOS Experiments: • Pipeline: Based on standard VGOS control files • Bands: B&C channels were selected (ionospheric search disabled) • Fitting: Fringe fitting was performed using Y-polarization only Note: • SESHAN25 (Sh), SESHAN13 (S6), TIANMA65 (T6), TIANMA13 (T1), URUMQI (Ur), URUMQI13 (Um) • AOV057 and AOV062 failed to extract phase delay • VO5148, two VGOS antennas are about 6km