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Short-baseline interferometry local-tie experiments at the Onsala Space Observatory.

Eskil Varenius¹, Rüdiger Haas¹, Tobias Nilsson²

¹Department of Space, Earth and Environment, Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden.

Journal of Geodesy

|April 27, 2021

Summary

Geodetic very long baseline interferometry (VLBI) measurements at Onsala Space Observatory achieved sub-millimetre precision for twin telescope coordinates. These new coordinates enhance future geodetic VLBI data analysis and station positioning accuracy.

Keywords:

Geodetic VLBI Geodetic core sites Onsala Space Observatory Onsala twin telescopes Short-baseline interferometry VGOS

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Area of Science:

Geodesy
Radio Astronomy
Earth Observation

Background:

Geodetic very long baseline interferometry (VLBI) is crucial for precise Earth observation.
The Onsala Space Observatory operates multiple VLBI stations, including legacy and next-generation VGOS systems.
Accurate station coordinates are fundamental for geodetic measurements and global reference frame maintenance.

Purpose of the Study:

To analyze interferometric measurements from three geodetic VLBI stations at Onsala.
To determine high-precision coordinates for the Onsala twin telescopes (VGOS).
To assess the performance of different delay types (group-delay vs. phase-delay) in geodetic VLBI analysis.

Main Methods:

Conducted 25 VLBI observation sessions in 2019-2020 using X-band frequencies.
Employed the 'Solve' package for data pre-processing and ambiguity resolution.
Utilized the 'ASCOT' package for station position determination, including modeling gravitational deformation.

Main Results:

Achieved weighted root mean square post-fit residuals of 10-15 ps (group-delay) and 2-5 ps (phase-delay).
Determined the coordinates of the Onsala twin telescopes with sub-millimetre precision in the VTRF2020b frame.
Observed an offset of a few millimeters in the up-component between positions derived from phase-delay and group-delay.

Conclusions:

The new sub-millimetre precise coordinates for the Onsala twin telescopes are recommended for future geodetic VLBI operations.
Phase-delay measurements show potential for high-precision geodetic applications but require further investigation regarding observed offsets.
Continued modeling of elevation-dependent effects may clarify discrepancies between group-delay and phase-delay results.