Determination of Structure Corrections using Geodetic VLBI Observations of Fiducial Extragalactic Radio Sources

We present the further development of the mathematical technique for calculating the structure corrections using VLBI images of fiducial extragalactic radio sources entering the celestial reference frame. In contrast to techniques described in the literature, the proposed approach can be applied to arbitrary images rather than to images which can be represented by a few Gaussian or delta functions. This is especially topical in view of the appearance of new sophisticated and high-precision image-reconstruction techniques different from the conventional CLEAN procedure or model fitting. The calculation efficiency of the structure corrections is ensured by using the algorithm of fast Fourier transform. We apply the proposed method to analyze a sufficiently representative sample of 36 fiducial extragalactic sources entering the celestial reference frame and illustrate its use for four sources, 1357+769, 0229+131, 2201+315, and 2200+420, each of them belonging to one of the four structure-index classes.