The impacts of source structure on geodetic parameters demonstrated by the radio source 3C371

Abstract

Abstract. Closure quantities measured by very long baseline interferometry (VLBI) observations are independent of instrumental and propagation instabilities and antenna gain factors, but are sensitive to source structure. A new method is proposed to calculate a structure index based on the median values of closure quantities rather than the brightness distribution of a source. The results are comparable to structure indices based on imaging observations at other epochs and demonstrate the flexibility of deriving structure indices from exactly the same observations as used for geodetic analysis and without imaging analysis. A three-component model for the structure of source 3C371 is developed by model-fitting closure phases. It provides a real case of tracing how the structure effect identified by closure phases in the same observations as the delay observables affects the geodetic analysis, and investigating which geodetic parameters are corrupted to what extent by the structure effect. Using the resulting structure correction based on the three-component model of source 3C371, two solutions, with and without correcting the structure effect, are made. With corrections, the overall rms of this source is reduced by 1 ps, and the impacts of the structure effect introduced by this single source are up to 1.4 mm on station positions and up to 4.4 microarcseconds on Earth orientation parameters. This study is considered as a starting point for handling the source structure effect on geodetic VLBI from geodetic sessions themselves.

Observable quality assessment of broadband very long baseline interferometry system

“…We processed the 21 VGOS sessions to determine error contributions in group delay observables, including measurement noise and source structure effects, by doing closure analysis (Xu et al 2016(Xu et al , 2017Anderson and Xu 2018). We adopted the same procedure of closure analysis for the VGOS sessions as was developed for the CONT14 sessions described in Anderson and Xu (2018).…”

High-resolution radio imaging of two luminous quasars beyond redshift 4.5

“…Such structures may have adverse effect on the accuracy of parameter estimates and could limit the overall precision of the reference frame (e.g. Charlot 1990;Xu et al 2017). One way of characterizing the astrometric quality of the sources is calculating their structure index (Fey & Charlot 1997) and its modified value for a continuous scale (SI c ; Fey et al 2015).…”

Source Structure and Measurement Noise Are as Important as All Other Residual Sources in Geodetic VLBI Combined

“…Plots of residual ionosphere‐free group delay versus the minimum elevation angle of the two stations in each observation. The sources are 0727−115 (1.8), 0059+581 (1.9), 0642+449 (3.0), and 0212+735 (3.3), where the numbers in parentheses following the source names are the continuous structure indices of the sources for the CONT14 observations from Xu et al (), with larger values indicating more significant structure. Unflagged observations are shown as blue circles.…”

“…The baseline brightnesses were calculated from the CONT14 imaging structure models and are shown relative to the total model flux densities of the individual sources. The sources are 0727−115 (1.8), 0059+581 (1.9), 0642+449 (3.0), and 0212+735 (3.3), where the numbers in parentheses following the source names are the continuous structure indices of the sources for the CONT14 observations from Xu et al (), with larger values indicating more significant structure. See Figure for the description of data point symbols.…”