hide
Free keywords:
Very long baseline interferometry (VLBI),IVS, Space geodesy, CONT17, Source structure
Abstract:
An ideal target for geodetic very long baseline interferometry (VLBI) is a strong and point-like radio source. In reality, most
celestial sources used in geodetic VLBI have spatial structure. This is as a major source of error in VLBI Global Observing
System (VGOS) and also affects legacy S/X observations. Source structure causes a systematic delay, which can affect the
geodetic estimates if not modelled or otherwise accounted for. In this work, we aim to mitigate its impact by extending
the stochastic model used in the least-squares fitting of the VLBI group delays. We have developed a weighting scheme to
re-weight the observations by parameterizing the source structure component in terms of closure delays and jet orientation
relative to the observing baseline. It was implemented in the Vienna VLBI Software. To assess the performance of the extended
stochastic model, we analysed the CONT17 legacy sessions and generated suitable reference solutions for comparison. The
effects of re-weighting were evaluated with respect to the session fit statistics, source-wise residuals, and geodetic parameters.
We find that this relatively simple noise model consistently improves the session fit by about 5% with moderate variation from
session to session. The geodetic estimates are not affected to a significant level by this new weighting method. Source-wise
we see improved post-fit residuals for 63 out of a total of 91 sources observed.
