Investigation of the positional instability of reference points for the Simeiz-Katziveli collocation station

We analyze the local geodetic ties between the VLBI, LLR, and GPS reference points of the Simeiz-Katziveli collocation station. The conclusion about the instability of this geodynamic test area is confirmed. We conclude that regular, with a period of 1–2.5 years, redeterminations of the local geodetic ties at this collocation station are necessary. A linear model of the time variation in the estimates of the local geodetic ties is constructed for this test area. The estimates of the local geodetic ties are compared with the differences between the corresponding coordinates of the reference points specified in ITRF2000. We conclude that there are systematic errors in ITRF2000 related to an incorrect determination of the velocities for the reference points of the collocation station with identical DOMES numbers. We suggest assigning different DOMES numbers to the reference points of unstable geodynamic test areas. The estimates of the local geodetic ties are compared with the differences between the corresponding coordinates of the reference points obtained from individual VLBI, LLR, and GPS solutions. These were found to be in disagreement.