Federal Agency for Cartography and Geodesy

European Earth system science increasingly depends on seamless access to authoritative and interoperable spatial data across administrative and national borders. While many European research infrastructures focus on scientific data production, long-term sustainability and reproducibility also require the systematic inclusion of legally mandated public-sector geodata, which can complement initiatives such as the European Open Science Cloud (EOSC). This contribution presents how Germany’s Spatial Data Infrastructure (GDI-DE), through its national discovery and access portal Geoportal.de and its European coordination activities, supports this integration. Geoportal.de is Germany’s central discovery and access portal for geospatial data and services provided by federal, state and local authorities. It implements a federated, legally grounded model in which hundreds of data providers publish INSPIRE-compliant metadata and services through standardized interfaces. This allows scientists to discover, evaluate and access authoritative reference data, environmental monitoring data and thematic geodata that are often not available through purely research-driven infrastructures, thereby providing a stable backbone for FAIR-aligned access to public-sector Earth system data in Germany.Beyond national service provision, the German Coordination Office for Spatial Data Infrastructure actively contributes to European technical coordination through the MIG-T, the permanent technical subgroup of the INSPIRE MIG. Within this framework, the coordination office of the GDI-DE coordinated the German stakeholder involvement in the recent INSPIRE consolidation process, which aimed at simplifying and modernizing the INSPIRE framework while ensuring continuity for operational infrastructures. This national coordination complemented parallel activities across Europe, helping to align national and European perspectives on the future of INSPIRE.We argue that the combination of legally mandated national SDIs and European-level technical coordination is a key enabler for Earth system science, providing long-term, quality-controlled and interoperable access to public-sector geodata while allowing research infrastructures to focus on scientific value generation.

Abstract We present an evaluation of the novel absolute quantum gravimeters AQG-A02 and AQG-B10 by the French manufacturer Exail with an emphasis on the user's application and outlook for integration into the routine gravity measurements of the German Federal Agency for Cartography and Geodesy (BKG). Since the delivery of these instruments to BKG, test measurements have been performed at the well-established gravity reference stations in Wettzell and Bad Homburg. Our measurements confirm a sensitivity of 500 nm s−2 Hz−1/2 at a quiet site, as specified, equivalent to a precision of 10 nm/s2 after 1-h integration time, and a combined uncertainty on the order of 100 nm/s2, based on a comparison to the local gravity reference function. We conclude that, as of yet, both AQGs do not reach the accuracy of FG5-type gravimeters, but provide advantages for continuous measurements and operation. Despite occasional technical issues with system reliability and pending research on improving the systematic errors, we expect the AQGs will find a central role in BKG's routine gravity measurements in the near future.

The resilience of Global Navigation Satellite System (GNSS) usage against spoofing attacks can be increased by signal monitoring algorithms aiming to detect a spoofing signal at the acquisition stage of GNSS receiver signal processing. A common approach is to search for the presence of multiple correlation peaks in the absolute value of the Cross-Ambiguity Function (CAF). In this context, it is particularly challenging to detect spoofing signals with a correlation peak closely aligned to that of the authentic signal, as is the case at the early stage of a coherent spoofing attack. In the present work, a spoofing detection method is proposed that monitors the magnitude of the CAF by means of clustering techniques. It is designed to detect the pull-off during a coherent power-matched spoofing attack already at an early stage. The method is evaluated for the GPS L1 C/A signal based on a static scenario from the Texas Spoofing Test Battery (TEXBAT) data set as well as for the Galileo E1-B signal based on a real-world digital snapshot recording in the E1 frequency band that is augmented by emulated spoofing signals at the level of digital signal processing.

Abstract The radio telescopes of the European VLBI Network (EVN) and the University of Tasmania (UTAS) conducted an extensive observation campaign of the European Space Agency’s (ESA) Mars Express (MEX) spacecraft between 2013 and 2020. The campaign, carried out under the Planetary Radio Interferometry and Doppler Experiment (PRIDE) framework, aimed to study interplanetary phase scintillation and assess the noise budget in the closed-loop Doppler observations. The average closed-loop Doppler noise was determined to be approximately 10 mHz at a 10-s integration time, reaffirming the technique’s suitability for radio science experiments. We evaluated how different observational parameters such as the solar elongation, antenna size, and elevation angle impact the Doppler noise. A key part of the analysis involved comparing results from co-located telescopes to investigate system noise effects. Co-located telescopes at both Wettzell and Hobart provided highly consistent results, with any deviations serving as diagnostic tools to identify station-dependent issues. Additionally, the use of phase calibration tones during spacecraft tracking showed that the instrumental noise contribution is of the order of 5 $\%$ of the total noise. This study provides a detailed noise budget for closed-loop Doppler observations with VLBI telescopes while emphasizing the effectiveness of the co-location method in isolating system-level noise. These findings are important for optimizing future radio science and VLBI tracking missions using stations outside the the Deep Space Network (DSN) and European Space Tracking (ESTRACK) network.

The observations of the four space-geodetic techniques (GNSS, SLR, VLBI, DORIS) are used for the computation of the International Terrestrial Reference Frame (ITRF) and for the realisation of its geodetic datum as well as (except VLBI) for the precise orbit determination of Earth-observing satellites. The ITRF itself is fundamental for a broad variety of scientific and societal applications such as Earth monitoring and positioning, relevant for satellite companies, logistics, and finally new techniques like autonomous driving. However, all four techniques still suffer from unknown systematic measurement or modelling errors which makes the estimation of bias parameters inevitable.The Geodetic Observatory Wettzell (GOW), Germany, with its unique and ideal test environment comprising multiple GNSS antennas, three VLBI antennas, two SLR telescopes, a DORIS beacon, and numerous other sensor systems provides the opportunity to systematically identify, quantify, understand, and compensate system-specific measurement errors. The installation of a so-called common target (CT) in 2017 and the realisation of a common clock (CC) enables a profound analysis of space-geodetic measurements. The CT is connected to the clocks of the space-geodetic techniques via delay-compensated fibre links which allows so-called ‘closure in time’ experiments.Within the recently established DFG research unit ‘Clock Metrology: Time as a New Variable in Geodesy’, one project at DGFI-TUM focuses on the investigation of time-related and technique-specific errors using ‘closure in time’ experiments at the GOW. Therefore, completed experiments involving the CT are analysed and enhanced experiments will be planned and conducted. With the aid of the CC, the source of present measurement discrepancies will be investigated and resolved. We present the current state of our work with the main focus on the analysis of VLBI and SLR observations of the two SLR and three VLBI systems at GOW.

Abstract The difference UT1-UTC is the most variable quantity among the Earth Orientation Parameters (EOP) with significant unpredictable variation. It can be measured only with the quasi-space-fixed technique VLBI. The IVS organizes two different VLBI observation campaigns: The bi-weekly 24-hour Rapid campaigns and the daily 1-hour Intensive sessions. As a result, two independent UT1-UTC time series are estimated and published as official IVS EOP-S and EOP-I products. These have different strengths and weaknesses in terms of continuity and accuracy, but both are characterized by irregular temporal resolution. We present the current activities of BKG towards a combined processing of VLBI Intensive and Rapid data in one common adjustment. In this way, we unify the strengths of both sessions and generate a UT1-UTC time series characterized by a daily, continuous and temporally regular resolution, e.g., at 12:00 UTC. We achieved a significant improvement in accuracy of 35% lower WRMS values compared to the regular session-wise Intensive-only solution. By using a continuous EOP parameterization, the accuracy is almost at a constant level and less dependent on the irregularity of the VLBI observation period. The processing is based on homogenized, datum-free NEQs which allow a rigorous combination on the normal equation level instead of the observation level. Based on the improved combination method, we intend to set up a new operational VLBI EOP product at BKG. Its characteristics make it suitable as an input for EOP prediction algorithms.

We present BKG´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.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>The rapid determination of the Earth's phase of rotation, expressed through the Earth rotation parameter dUT1, is one of the core tasks of geodetic Very Long Baseline Interferometry (VLBI). To ensure a low latency between observation and analysis results, dedicated 1-hour-long VLBI sessions, so-called Intensives, are regularly observed. Two of these Intensive programs, namely INT2 and INT3, are organized and monitored by the joint IVS operation center DACH. </p><p>Within this study, a detailed overview over the last five years of the VLBI Intensive observing programs INT2 and INT3 is provided. INT2 sessions are typically observed on Saturdays and Sundays using a single baseline and a recording rate of 256 Mbps. INT3 sessions are multi-baseline Intensives with up to five stations, observed on Mondays with a recording rate of 1 Gbps. </p><p>Starting in 2019, the scheduling strategy of the INT3 sessions was significantly changed, leading to a reduction of the estimated average dUT1 formal errors by 25% (from (6.1 ± 2.0) µs to (4.5 ± 1.0) µs) for the 4-station network. The improvement w.r.t. dUT1 mean formal errors for the 5-station network is 45% (from (6.3 ± 1.7) µs to (3.5 ± 0.5) µs). </p><p>The best performing INT2 baseline is observed between station MK-VLBA (USA) and WETTZELL (Germany). Mid-2020, the same change was applied for these INT2 sessions, leading to a reduction in the average dUT1 mean formal error of 44% (from (11.7 ± 5.7) µs to (6.6± 4.7) µs). </p><p>Furthermore, comparisons of dUT1 estimates from various analysis centers w.r.t. IERS EOP C04 and JPL EOP2 are conducted. It is revealed that the previously mentioned INT2 baseline shows a bias of only -2.5 µs and 1.9 µs based on the estimates provided by the analysis centers Goddard Space Flight Center (GSF) and Bundesamt für Karthographie und Geodäsie (BKG), respectively, when compared with JPL EOP2. In contrast, the bias is 10.4 µs and 14.9 µs w.r.t. IERS EOP C04. </p><p>Besides analyzing dUT1 formal errors, the latency of the dUT1 results is compared. For INT3 sessions, results are typically available within 24 hours, while it takes two to three days for INT2 sessions, due to observations occurring on weekends. This reveals that the increased data volume recorded by the up to five stations with 1 Gbps does not increase the latency of the analysis results and dUT1 estimates can be obtained within 24-hours. </p><p>Overall, this work provides a detailed insight into the INT2 and INT3 session performances, revealing a strong positive trend in the precision of dUT1 measurements over the last few years.</p>

<p>The ITRF2020 is the upcoming realization of the International Terrestrial Reference Frame. As the successor of the ITRF2014, it is based on an inter-technique combination of all four space-geodetic techniques, i.e., VLBI, GNSS, SLR and DORIS, and it is based on contributions from different institutions around the world. In this context, the Combination Centre of the International VLBI Service for Geodesy and Astrometry (IVS) – operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) and the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM, Germany) – generates the VLBI intra-technique combination for ITRF2020 utilizing the individual contributions of multiple IVS Analysis Centres (AC).</p><p>For the contribution to the ITRF2020 solution, sessions containing 24h VLBI observations from 1979 until the end of 2020 are reprocessed by 11 ACs and submitted to the IVS Combination Centre. All individual sessions include datum-free normal equations containing station coordinates and source positions as well as full sets of Earth Orientation Parameters (EOP) in the required SINEX format. For ensuring consistently combined solutions, time series of EOP and station coordinates, as well as a VLBI-only Terrestrial Reference Frame (VTRF), have been investigated.</p><p>This contribution focuses on detailed investigations concerning the session-dependency of the scale and the impact of the individual AC contributions to the combination. Thereby significant differences of the scale estimates from the different session types are investigated. Also, the evaluation of the ACs’ contributions to the combined solution will be presented.</p>