Combination of GNSS and VLBI data for consistent estimation of Earth Rotation Parameters

Abstract

<p>We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.  The main goal of the combined analyses of the two different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, i.e., mainly Earth Rotation Parameters (ERPs), but also station coordinates and tropospheric parameters through local ties and atmospheric ties, respectively.</p><p>Based on our previous combination studies using GNSS data and VLBI Intensive sessions on a daily and multi-day level, we generate a consistent, low-latency ERP time series with a regular daily resolution for polar motion and dUT1. We achieved in this way a significant accuracy improvement of the dUT1 time series and a slight improvement of the pole coordinates time series, comparing ERPs from the combined processing with the individual technique-specific ERPs.</p><p>In our recent studies, we extend the combination of GNSS and VLBI Intensive sessions by adding VLBI 24-hour sessions in order to exploit the benefit of the combination to its maximum extend. We analyse the impact of the combination on the global parameters of interest, i.e., mainly dUT1, polar motion and LOD, but also on station coordinates.</p><p>BKG’s primary interest is the combination of GNSS and VLBI data on the observation level. However, the current combination efforts are based on the normal equation level using technique-specific SINEX files as a starting point.</p>

On the Improvement of Combined EOP Series by Adding 24-h VLBI Sessions to VLBI Intensives and GNSS Data

“…Figure 2 summarizes the processing steps and the entire combination procedure. It is an extension of the combination scheme presented in Lengert et al (2022). It is extended by the multi-day intra-technique VLBI combination (n-VLBI) and the final combination (COMBI FIN) presented hereafter.…”

“…Studies have shown that the selection of the reference point with no correction does not affect the estimated dUT1 values. The addition of Galileo observations into the analysis process has no noticeable effect on the magnitude of the bias (Lengert et al 2022). Furthermore, the EOP of the last day of each GNSS Rapid are extracted and the EOP offsets of the first two days of the 3-day polygons are pre-eliminated.…”

“…The chosen scaling factor reflects almost the ratio between the technique-or session-specific observation duration. Detailed information on the determination of the appropriate scaling factor can be found in Lengert et al (2022). For the solution COMBI RAP, the n-GNSS NEQ is combined with the n-VLBI INT NEQ, whereas for COMBI FIN, the intra-technique combined n-VLBI NEQ is used instead, i.e.…”

“…. The comparison epoch is 12 h. The WRMS values of the singleday VLBI INT solution (with fixed LOD a priori values) and the weekly intra-technique combination (7-VLBI INT) are depicted additionally.Detailed information about the session-wise singletechnique solutions (GNSS, VLBI INT, VLBI R1/R4), intratechnique combined solutions (n-VLBI INT, n-GNSS) and the rapid combination (COMBI RAP) as well as the sessionwise combination of GNSS and VLBI R1/R4 can be found inLengert et al (2021).…”