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GASV: A New VLBI analysis software for Geodesy and Astrometry

Dang Yao, Yuan-wei Wu, Xu-hai Yang

TL;DR

GASV introduces a Python-based VLBI analysis package that targets ease of use while delivering high-precision geodetic and astrometric parameter estimation from VLBI data. It implements a modular delay model per IERS conventions, robust ambiguity resolution, ionospheric corrections, outlier handling, and both session-wise and global analysis capabilities, exporting standard products such as SINEX and vgosDB. Performance tests on IVS INT, Regular, CONT17 data and SINEX histories show GASV achieves accuracy comparable to established centers like BKG and USNO, with strong consistency in EOPs, station coordinates, and ICRF3/source positions. The work positions GASV as a scalable, open-source tool for single-session VLBI analysis and a stepping-stone toward integrated multi-technology solutions for unified celestial and terrestrial reference frames.

Abstract

We present GASV, a novel Python-based software package specifically designed for the analysis of Very Long Baseline Interferometry (VLBI) data. Developed with ease of installation and user friendliness in mind, GASV supports both pipeline and interactive processing modes. The software processes VLBI baseline delays and rates in standard formats such as HOPS outputs and NGS card files to estimate key geodetic and astrometric parameters, including station coordinates, Earth Orientation Parameters, source coordinates, clock parameters, and atmospheric models. We evaluate the capabilities and performance of GASV, demonstrating that its parameter estimation accuracy for IVS INT, Regular, and CONT sessions is comparable to that achieved by the VLBI analysis centers at BKG and USNO. As a state-of-the-art tool, GASV not only enables high-quality single-session data processing but also but also supports global analyses of long-term SINEX files, generating Celestial Reference Frame and Terrestrial Reference Frame solutions with reliable accuracy.

GASV: A New VLBI analysis software for Geodesy and Astrometry

TL;DR

GASV introduces a Python-based VLBI analysis package that targets ease of use while delivering high-precision geodetic and astrometric parameter estimation from VLBI data. It implements a modular delay model per IERS conventions, robust ambiguity resolution, ionospheric corrections, outlier handling, and both session-wise and global analysis capabilities, exporting standard products such as SINEX and vgosDB. Performance tests on IVS INT, Regular, CONT17 data and SINEX histories show GASV achieves accuracy comparable to established centers like BKG and USNO, with strong consistency in EOPs, station coordinates, and ICRF3/source positions. The work positions GASV as a scalable, open-source tool for single-session VLBI analysis and a stepping-stone toward integrated multi-technology solutions for unified celestial and terrestrial reference frames.

Abstract

We present GASV, a novel Python-based software package specifically designed for the analysis of Very Long Baseline Interferometry (VLBI) data. Developed with ease of installation and user friendliness in mind, GASV supports both pipeline and interactive processing modes. The software processes VLBI baseline delays and rates in standard formats such as HOPS outputs and NGS card files to estimate key geodetic and astrometric parameters, including station coordinates, Earth Orientation Parameters, source coordinates, clock parameters, and atmospheric models. We evaluate the capabilities and performance of GASV, demonstrating that its parameter estimation accuracy for IVS INT, Regular, and CONT sessions is comparable to that achieved by the VLBI analysis centers at BKG and USNO. As a state-of-the-art tool, GASV not only enables high-quality single-session data processing but also but also supports global analyses of long-term SINEX files, generating Celestial Reference Frame and Terrestrial Reference Frame solutions with reliable accuracy.
Paper Structure (23 sections, 46 equations, 12 figures, 5 tables)

This paper contains 23 sections, 46 equations, 12 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Structure and Algorithm
  3. Structure
  4. VLBI Delay Model
  5. Ambiguity Resolution Algorithm
  6. Ionospheric Correction
  7. Outlier Flagging and Reweighting
  8. Reweighting
  9. Session Analysis
  10. Global Analysis
  11. Performance evaluation
  12. Parameter Setting
  13. IVS Intensive Sessions
  14. IVS Regular Sessions
  15. IVS CONT17 Session
  16. ...and 8 more sections

Figures (12)

  • Figure 1: Structure of GASV software. The workflow begins with INPUT data, including the Post-Process results (MarkIV/NGS), station log, control file, and a priori file. These inputs are processed by the MAIN module. The OUTPUT module produces four result types: vgosDB, EOP files, Spool files, and SINEX files
  • Figure 2: Schematic illustration of closure delay. Letters A, B, C and D denote four stations, while $\tau$ represents the baseline delay.
  • Figure 3: Software screenshot showing observation residuals of 21DEC20XA session with outlier selection. The software supports residual visualization by station, baseline, and source; it also allows for quick configuration of estimation parameters and saves processing results.
  • Figure 4: Comparison of the results of UT1 among different analysis centers from 2020 to 2023, w.r.t. C04. The left panel shows the INT1 result, the right panel shows the INT2 and INT3 result.
  • Figure 5: Estimated results of EOP from 2020 to 2024, w.r.t. C04. The upper panel presents results for polar motion and UT1, where the left Y-axis corresponds to polar motion results and the right Y-axis represents the UT1 results. The lower panel displays results for the CPO.
  • ...and 7 more figures