Consistently combined Earth Rotation Parameters at BKG - Adding SLR data to VLBI and GNSS

We present BKG´s current activities in the field 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 ERPs. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP series with latencies of about 1-2 or 14 days, depending on the input data 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 datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level. Our current activities in the area of multi-technique combination are focused on augmenting the combination of GNSS and VLBI data with SLR data. It is expected that the SLR technique has the potential to improve the combined ERP solution, especially the highly variable dUT1 parameter, by providing a stable LOD contribution. Due to its short latency of about 1 day, the SLR-DAILY product is basically well suited to expand the database of our Rapid EOP series, which is currently only based on GNSS Rapid and VLBI Intensives data. However, the official SLR-DAILY product of the ILRS is a 7-day solution that explicitly contains polar motion (only as constant offsets over 24 hours) and LOD, but no dUT1 parameters and no polar motion rates. Therefore, this solution is not optimal for our combination approach because the parameterization of the ERPs is not identical to the other techniques that uses offsets and rates for all ERPs. However, the in-house ILRS Analysis Center allows us to generate a customized SLR solution that has an improved parameterization of the ERPs and, thus, is optimized for the multi-technique combination. We investigated the SLR data with respect to the quality of the resulting ERP series and integrated the data into our combination process. We present the impact of SLR on the combined ERP product and the challenges of extending the combination with this data.