Applying Precision Criteria to the Radio Sources in the Daily IVS Sessions

The quality of a geodetic network is classically determined with the precision criteria computed from the cofactor matrix of the unknown parameters. One of the precision criteria having more information compared to the Helmert position error and the mean error of the unknown parameters is the Helmert mean error ellipsoid. In two-dimensional networks – and the celestial reference frame realized by extragalactic radio sources can be considered as such - the Helmert mean error ellipse consists of three parameters which are the semi-major and semi-minor axis of the error ellipse and the direction of the semi-major axes. In a well-designed geodetic network, the error ellipses should have homogenous structures. In other words, the semi-axes of the error ellipses for all radio sources should be similar. In this study, daily IVS sessions of the CONT17 were evaluated with The Potsdam Open Source Radio Interferometry Tool (PORT) and the parameters of the Helmert mean error ellipses were computed for the radio sources in each session. Also, the results are compared with the number of observations and the angular position of the radio sources. As a result of this study, it can be seen how the precision criteria are affected depending on the angular position of the radio sources.