Earth Orientation Parameters — Combination of Results Obtained by Different Techniques

Abstract

The recently developed method of ‘combined smoothing’ is shortly introduced and its main philosophy presented. The method is tested with simulated data in order to demonstrate that the method is capable of removing both long-term and stepwise systematic errors in time derivatives of certain Earth Orientation Parameters measured by satellite methods.

It is then applied to combine the observations by VLBI (universal time, celestial pole offsets) with the time derivatives of the same quantities (length-of-day, celestial pole offset rate) measured by GPS. The input data are typically given in weekly (VLBI) and daily (GPS) intervals, both resulting curves (mutually consistent function values and time derivative values) are defined at all original epochs with any observation, i.e. at least in daily intervals.

It is shown that the result of such combination is practically free of long-term systematic errors of GPS observations. It takes over the long-term stability of VLBI results, provides automatically the necessary calibration of GPS results against VLBI, and fills in the gaps in less dense VLBI measurements by more frequent and short-term stable GPS observations.