Method for the combination of sub-daily Earth rotation from GPS and VLBI observations: A review

Abstract

On the basis of homogeneous normal equation systems, a combination procedure of Earth orientation parameters from Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) observations was developed. The combination's focus and intent was to establish sub-daily polar motion (PM) and universal time (UT1) over a long 13-year time period. Estimated time series with an hourly resolution and a standard for PM and UT1-TAI tidal variations (dUT1). In both cases, the 14-day nutation corrections were calculated at the same time as the ERPs. The combination method required the protection of the strengths of both techniques. At the same time, it just required a minimum of constraints to de-correlate or stabilize. Hereby, a PM time series, whose accuracy is governed by GPS observations, was calculated. This system therefore benefits from the fact that at the same time VLBI received estimates of nutation and dUT1. For the dUT1 calculation, where the high-frequency variations are given by GPS while the long-term pattern is established by VLBI, an even bigger enhancement can be seen. The approximate model of the combined tidal PM and dUT1 was calculated primarily from the GPS observations. Ultimately, for the first time the integrated tidal model completely incorporates the geometric advantages of VLBI and GPS observations.