<p>We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.&#160; 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&#8217;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>
<p>We present BKG&#180;s current activities in the area of combined data processing of different space-geodetic techniques. The primary goal of the combined analyses is the improvement of the consistency between the techniques through common parameters, mainly Earth Rotation Parameters (ERP), and thereby to improve also the resulting ERP. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP time series with latencies of about 1-2 or 14 days, depending on the input data we used. In this way, we achieved a significant improvement in accuracy, especially for the dUT1 series, compared to the individual technique-specific solutions. The processing is based on homogenized datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level.</p> <p>Our main objective is to generate an ERP product that is characterized by a continuous, daily and regular resolution and the shortest possible latency, especially for the highly variable dUT1. The mandatory requirement for achieving these characteristics is the rapid availability of the input data on the daily basis, especially of the VLBI Intensive sessions. The time series of daily SINEX files of the legacy (S/X) VLBI Intensive sessions show some gaps in the past. The reasons for this are manifold and can be found throughout the entire VLBI processing chain, i.e., from the observation, i.e. station ability to participate, to the analysis, i.e. the data quality revision. However, in the last two years, an increasing number of VGOS Intensive campaigns has been conducted in addition to the legacy Intensives. As a result, the Intensive series is nowadays almost without gaps and there are even more than one Intensive sessions (up to 6) available per day. In our recent studies, we compare the VGOS and legacy Intensives data in terms of their latency and the quality of the resulting dUT1 estimates and integrate them into our combination process. We highlight also the challenges of extending the combination with the new VGOS data. Its incorporation will eventually pave the way for establishing an operational ERP product at BKG.</p>
<p>We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI, GNSS and SLR data. The main goal of the combined analyses of the three different space-geodetic techniques is the improvement of the consistency between the techniques through common parameters, i.e., mainly Earth Rotation Parameters (ERPs). The combination is based on homogenized, datum-free NEQs which allow a rigorous combination on the normal equation level instead of the observation level.</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 the second step, we extend the multi-day combination of GNSS and VLBI Intensive sessions by adding VLBI 24-hour sessions. The additional combination with VLBI R1/R4 data further stabilizes all ERPs twice per week and enables the estimation of high-precision ERP time series with a latency of about two weeks. With this combination approach, we obtained a further improvement in the dUT1 time series. For the pole coordinates time series, the accuracy of the estimates is almost at the same level as for the rapid combined solution.</p><p>In our recent studies, we want to investigate improvements in the representation of the ERP parameters of the VLBI 24-hour sessions. Furthermore, we want to extend the combination of GNSS and VLBI data by adding SLR sessions in order to exploit the benefit of the combination to its maximum extend. We expect that SLR improves the combined ERP solution in particular through a stable contribution of LOD. 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>Based on the improved combination method, we intent to set up a new operational BKG-ERP product.</p>
<p>We present the current activities of the Federal Agency for Cartography and Geodesy (BKG) towards a combined processing of VLBI and GNSS data.&#160; 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, as Earth Orientation Parameters (EOPs), but also station coordinates and tropospheric parameters through local ties and atmospheric ties, respectively.</p><p>The combination of GNSS data with VLBI 24-hour sessions and VLBI Intensive sessions is studied in detail w.r.t. EOPs to exploit he combination benefit to its maximum extend. We analyse the impact of the combination on the technique-specific parameters (e.g. dUT1), but also on common parameters (e.g. LOD, polar motion, station coordinates). When using GNSS data in combination with VLBI Intensive sessions, we can demonstrate an accuracy improvement of the dUT1 time series.</p><p>We also study the combination of troposphere parameters, focusing first on the validation of the technique-specific troposphere parameters at VLBI-GNSS co-located sites and on the modelling of the corresponding atmospheric ties.</p><p>BKGs 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>
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