Network of Stations of the Crimean Geodynamic Test Area: Local Ties Variations and Their Comparison with the Values Obtained in the ITRF2020 Reference Frame

The Simeiz–Katzively Crimean geodynamic test area is one of the unique site in the world, in which several space geodesy observation stations are located, namely, RT-22 radio telescope (CRIMEA, CDP no. 7332), satellite laser ranging (SLR) stations 1873 Simeiz and 1893 Katzively, permanent GNSS stations CRAO and KTVL, and the marker of mobile SLR station 7561 Simeiz. Four local survey geodetic campaigns and five GNSS campaigns were performed to determine local ties between space geodesy stations and basic markers on this site. As a result of campaigns, the coordinates of points (space geodesy stations and markers) in the Simeiz–Katzively Crimean geodynamic test area in the ITRF2000 reference frame at epoch 2004.6 were estimated. Local ties between basic site points were determined as differences between positions of the corresponding points and the position of the RT-22 radio telescope. Deviations from the average values of local ties at the sites of the RT-22 radio telescope and the SLR station of CrAO vary within the limits of up to 3.6 and 6.4 mm, respectively. Actually, they are within the limits of determination errors of local ties. The wide range of local ties variations for the mobile SLR station (7561) is caused by the physical damage of this marker and excavation works carried out around it between observation campaigns. The local ties for points at the site of the SLR station of CLO of the Main Astronomical Observatory of the National Academy of Sciences of Ukraine vary in a very wide range because this site has a local movement in the southern direction with a substantial velocity. The coordinates of the space geodesy stations in the Simeiz–Katzively Crimean geodynamic test area are available in the ITRF2020 catalogue, so it was possible to compare the local ties calculated from its data with the ones obtained by processing the data of geodetic campaigns. The differences between the two types of local ties are very large (up to 45 mm). The reasons for these discrepancies could lie both in the errors of local ties obtained during the geodetic campaigns and in the errors of estimates of the space geodesy station coordinates at this site in the ITRF2020 catalog. The distance between SLR station 1893 Katzively and the RT-22 radio telescope (1893–7332) shows a special behavior due to the fact that the velocities given in the ITRF2020 catalog for all SLR stations at the Simeiz–Katzively Crimean geodynamic test area have the same values and, consequently, substantial local movements of the site around the 1893 Katzively station are not taken into account. Considering the substantial local movements of this site, the velocities of SLR stations at the Simeiz–Katzively Crimean geodynamic test area should be estimated separately for each station for future implementations of the International Terrestrial Reference System (ITRS), as has been done, for example, for permanent GNSS stations CRAO and KTVL.