Evaluation of VLBI Observations with Sensitivity and Robustness Analyses

Pakize Küreç Nehbit,Susanne Glaser,Susanne Lunz,Kyriakos Balidakis,Emine Tanır Kayıkçı,Nicat Mammadaliyev,Harald Schuh,Haluk Konak,Robert Heinkelmann

doi:10.3390/math8060939

Abstract

Very Long Baseline Interferometry (VLBI) plays an indispensable role in the realization of global terrestrial and celestial reference frames and in the determination of the full set of the Earth Orientation Parameters (EOP). The main goal of this research is to assess the quality of the VLBI observations based on the sensitivity and robustness criteria. Sensitivity is defined as the minimum displacement value that can be detected in coordinate unknowns. Robustness describes the deformation strength induced by the maximum undetectable errors with the internal reliability analysis. The location of a VLBI station and the total weights of the observations at the station are most important for the sensitivity analysis. Furthermore, the total observation number of a radio source and the quality of the observations are important for the sensitivity levels of the radio sources. According to the robustness analysis of station coordinates, the worst robustness values are caused by atmospheric delay effects with high temporal and spatial variability. During CONT14, it is determined that FORTLEZA, WESTFORD, and TSUKUB32 have robustness values changing between 0.8 and 1.3 mm, which are significantly worse in comparison to the other stations. The radio sources 0506-612, NRAO150, and 3C345 have worse sensitivity levels compared to other radio sources. It can be concluded that the sensitivity and robustness analysis are reliable measures to obtain high accuracy VLBI solutions.

Highlights

Very Long Baseline Interferometry (VLBI) is used to measure the arrival time differences of the signals that come from extragalactic radio sources to antennas separated by up to one Earth diameter
According to the sensitivity analysis of the CONT14 campaign, the subset of European stations, ONSALA60, WETTZELL, ZELENCHK, MATERA, YEBES40M, and partly NYALES20 have the best sensitivity levels based on all sessions, whereas BADARY provides the worst sensitivity level based on all sessions (Figure 1)
The sensitivity levels of the radio sources show that some radio sources in individual sessions have orders magnitude larger sensitivity levels, e.g., NRAO150, 3C345, 3C454.3, and 0506-612

Summary

Introduction

Very Long Baseline Interferometry (VLBI) is used to measure the arrival time differences of the signals that come from extragalactic radio sources to antennas separated by up to one Earth diameter. The main principle of the VLBI technique is to observe the same extragalactic radio source synchronously with at least two radio telescopes. Global distances can be measured with millimeter accuracy using the VLBI technique [1,2]. VLBI is a primary technique to determine global terrestrial reference frames and in particular their scale, celestial reference frame, and the Earth Orientation Parameters (EOP), which consist of universal. Since VLBI is the only technique that connects the celestial with the terrestrial reference frames, the technique is fundamentally different from the other space geodetic techniques. The radio sources are objects in the International Celestial Reference

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