New Solution of Earth Orientation Parameters 1900-1992 from Optical Astrometry, and its Linking to ICRF and ITRF

Abstract

In preceding years we collected and re-analyzed the optical astrometry data from 33 observatories, using a unique celestial reference frame. It was realized first by the Hipparcos Catalogue, and then by a group of our own Earth Orientation Catalogs (EOC), being obtained by combining Hipparcos/Tycho data with older ground-based observations. EOC catalogs, that are tied to Hipparcos Catalogue, are given in the International Celestial Reference Frame (ICRF). On the other hand, the underlying terrestrial reference frame is arbitrarily realized by adopted geographic coordinates (latitudes, longitudes) of participating stations. Small additional coordinate biases and drifts of individual stations are estimated in the solution, we also suppose that each station can exhibit apparent annual and semi-annual changes of geographic coordinates due to anomalous refraction. To remove the singularity of the solution, we apply 18 additional constraints, tying the biases, drifts and seasonal changes of individual stations. As a consequence, the terrestrial reference frame of the optical solution can deviate from the International Terrestrial Reference Frame (ITRF) by a constant, linear drift and seasonal (annual, semi-annual) changes, in all three axes. To estimate these deviations, we compare our most recent EOP series, referred to catalog EOC-4, with the one provided by space techniques in the common interval of observations. The deviations found are then applied to our EOP solution to link it more precisely to ITRF.