Consistently Combined Earth Orientation Parameters at BKG—Extended by New VLBI Intensives Data

Abstract

AbstractThe Earth Orientation Parameters (EOPs) describe the rotation between the Terrestrial Reference Frame and the Celestial Reference Frame and represent an essential component of the Global Geodetic Reference Frame. This study presents the current activities of BKG in the area of combined processing of GNSS and VLBI data in one common adjustment with the main objective to generate a consistent combined EOP time series. In earlier studies, we have investigated different combination approaches using VLBI and GNSS data. We generate EOP series with latencies of about one to 14 days, depending on the input data we used. In this way, a significant improvement in accuracy compared to the individual technique-specific solutions was achieved, especially for the highly variable component dUT1. The combination process starts at the level of normal equations using an EOP parameterization with piece-wise linear offsets and a temporal resolution of one day. Our main objective is to generate a continuous, daily and regular EOP product with the shortest possible latency. The requirement for achieving these characteristics is the daily and rapid availability of the input data. In particular, the VLBI Intensive (INT) sessions play an important role in the precise and rapid estimation of the UT1-UTC component. Since 2020, an increasing number of VLBI Global Observing System (VGOS) INT campaigns has been conducted in addition to the legacy S/X INT sessions. The VGOS network is under continuous extension and the accuracy and latency of the VGOS INT sessions are at least at the level of the legacy S/X sessions. Therefore, an inclusion of the VGOS INT data is beneficial for rapid EOP estimation. The integration of the VGOS data into the combination process results in a constant slight decrease of the Weighted Root Mean Square (WRMS) level of the UT1-UTC residuals in comparison to the external EOP series. The growing number of available INT sessions with independent networks, up to four per day, increases the continuity and reliability of the combined EOP solution.