Imaging the Earth's interior has always been one of the key challenges in geosciences, as it is a prerequisite for understanding our planet's internal dynamics and the coupling between its inner and outer envelopes. Gravity measurements at different altitudes (ground, airborne and space-based observations) provide a unique imaging tool, as they supply direct information on mass changes at different spatio-temporal scales. Following decades of research, developments and industrial transfers, quantum technology has reached a high level of maturity and it is now possible to deliver operational quantum gravimeters offering various advantages with respect to devices that have been hitherto used.
Aligned with the objective of strengthening EU’s strategic autonomy and competitiveness, the Horizon Europe project EQUIP-G [1] started in June 2025. It represents the first step towards establishing the terrestrial segment of the pan-European quantum gravimetry infrastructure, revolving around a shared Instrumental Park and a network of absolute reference stations. For this purpose, quantum gravimeters, dual quantum gravi-gradiometers and an onboard quantum gravimeter are employed. Instruments are comprehensively tested, before being deployed in the field and will demonstrate, through innovative measurement strategies, the ability of the quantum gravity network to contribute to EU priorities, such as green deal, energy management and risk mitigation. Metrological oversight ensures that all collected quantum gravity data will be SI traceable. Data are managed in line with the FAIR principles and with a long-term perspective to establish a TCS for gravimetry within EPOS. EQUIP-G engages in strong community building, aimed at involving the entire European gravimetry community in the development of the long-term Instrumental Park initiative that will extend beyond the end of the project, democratizing the use of quantum gravity devices produced in Europe. This contribution provides an overview of the structure and main objectives of EQUIP-G and presents some preliminary achievements of the project.
EQUIP-G project is funded by the European Commission under the Horizon Europe program, grant number 101215427
[1] https://www.equip-g.eu
How to cite: Merlet, S., Dykowski, P., Carbone, D., Seoane, L., Reich, M., and Lautier-Gaud, J.: European QUantum Infrastructure Project for Gravimetry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8269, https://doi.org/10.5194/egusphere-egu26-8269, 2026.
Global Navigation Satellite Systems (GNSS) underpin a wide range of scientific and societal applications across a broad spectrum of timescales and disciplines, such as positioning navigation and timing (PNT), surveying, environmental and climate research, geohazard risk reduction, or space weather monitoring. Most of these applications rely on accurate clock corrections and precise orbit models based on a stable global reference frame, along with well defined conventions for antenna calibrations and system biases.
Established over 30 years ago, the International GNSS Service (IGS) meets these critical needs by continuously delivering a suite of openly accessible high-quality data, products, standards, and services. All IGS products adhere to a core principle: solutions from multiple analysis centres are rigorously compared, combined, and provided at maximum accuracy over latencies ranging from real-time to final.
We present the full range of IGS data and products available to the user community, with particular emphasis on recent additions and expansions. We also outline the critical components of the IGS infrastructure that enable these products, and discuss upcoming developments designed to foster broader community participation and innovation. Finally, we position IGS activities within the wider geodetic landscape, highlighting its role as a core component of the global geodesy supply chain.
How to cite: Dach, R., Martire, C., D'Anastasio, E., Bradke, M., Herring, T., and Ruddick, R.: The International GNSS Service - in support of GNSS applications in the frame of GGOS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7096, https://doi.org/10.5194/egusphere-egu26-7096, 2026.
The further development of space-geodetic station networks and analysis techniques is crucial for the realisation of terrestrial and celestial reference systems as well as to determine the Earth orientation parameters as the link between them with high accuracy and long-term stability. This requires geographically well-distributed and long-term sustained networks for all space-geodetic techniques: Global Satellite Navigation Systems (GNSS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Satellite/Lunar Laser Ranging (SLR/LLR), and Very Long Baseline Interferometry (VLBI).
The fundamental importance of geodetic reference frames has been recognised by the United Nations (UN) General Assembly resolution 69/266 on ‘A Global Geodetic Reference Frame for Sustainable Development’, adopted on 26 February 2015. The Global Geodetic Observing System Committee on Performance Simulations and Architectural Trade-Offs (GGOS-PLATO) investigates how to enhance the space-geodetic infrastructure designed (i) to acquire observations larger in quantity and better in quality by enhanced and additional ground stations, as well as (ii) to better tie the observation systems, e.g., by more co-locations on ground or in space, like ESA’s upcoming Genesis mission which will allow realising space ties between all four techniques for the first time.
This presentation provides an overview of recent GGOS-PLATO-related efforts regarding the sustainability and potential development of the existing networks of all space-geodetic techniques, including the aspect of co-located sites for the realisation of the terrestrial reference frame. The GGOS-PLATO studies aim to support the goals of the United Nations Global Geodetic Centre of Excellence (UN-GGCE), established in 2023 to coordinate the implementation of the UN resolution.
How to cite: Kehm, A. and Männel, B. and the GGOS-PLATO members and collaborators: Towards enhanced space-geodetic networks for a sustainable geodetic supply chain: Activities of the GGOS Committee on Performance Simulations and Architectural Trade-Offs (GGOS-PLATO), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16632, https://doi.org/10.5194/egusphere-egu26-16632, 2026.
The International Laser Ranging Service (ILRS) provides Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) observations and data products with a focus on Earth and Lunar science and engineering applications. The basic observables are the precise two-way time-of-flight of ultra-short laser pulses from ground stations to retroreflector arrays on satellites and the Moon and the one-way time-of-flight (TOF) measurements to space-borne receivers (transponders). The ILRS network is experiencing significant growth, with multi-techniques Core Sites exploiting the combined strengths of the various geodetic techniques, new low-cost systems, some being transportable. Some of the stations are also dedicating some of their efforts to tracking Space Debris, contributing to the maintenance of various data catalogs, helping support operations and continue their contributions to geodetic science. New stations joining the network, and new satellite missions supported, are strengthening the ILRS contribution to the International Terrestrial Reference Frame (ITRF) and expanding the spectrum of satellite applications supported by the Service. Improvements in Satellite Laser Ranging science products continue, enabled by new data processing and analysis techniques and better modeling. Fundamental physics applications continue to be supported through dedicated campaigns, as are time-transfer experiments and Lunar Laser Ranging (LLR) applications, and the support of new lunar missions.
It is the goal of this presentation to report on progress achieved by the International Laser Ranging Service (ILRS) during the last few years.
How to cite: Carabajal, C. C., Pearlman, M., Husson, V., Merkowitz, S., Blossfeld, M., Courde, C., and Croteau, M.: International Laser Ranging Service (ILRS) Status, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16896, https://doi.org/10.5194/egusphere-egu26-16896, 2026.
The strongest ionospheric currents flow in general in the E‑region (~90-135 km) due to the high conductivities produced by dayside ionization. The solar quiet (Sq) current system arises from neutral winds pushing plasma across Earth’s magnetic field, generating electric fields and ionospheric currents. The strongest current at low latitude is the daytime equatorial electrojet (EEJ). While magnetic perturbations associated with these ionospheric currents are measured globally—both from ground-based observations and from low Earth orbit (LEO)—direct measurements of E‑region neutral winds remain extremely sparse. This gap limits our ability to quantify neutral wind variability on day-to-day timescales and hinders a full understanding of lower–upper atmospheric coupling and its influence on space weather phenomena such as neutral density and plasma variations. These challenges motivate the use of magnetic observations to better constrain neutral wind variability.
In this presentation, we introduce atmospheric tides embedded in the neutral wind and their role in driving the wind dynamo. We illustrate how major tidal components contribute to the dynamo and the resulting magnetic signatures. We then present a data‑driven framework that combines ground-based magnetometer observations with ensemble modeling using the Thermosphere–Ionosphere–Electrodynamo General Circulation Model (TIEGCM) and an ionospheric electrodynamo model that simulates the full 3D current system and associated magnetic perturbations. This approach enables the estimation of hourly tidal variations at the TIEGCM lower boundary (~97 km altitude) and improves the representation of global EEJ variability. The simulation with improved winds is validated against LEO magnetic perturbation measurements, demonstrating that the agreement improves even in regions with limited data coverage. The results highlight the potential of magnetometer data to constrain tidal dynamics and enhance global modeling of equatorial electrodynamics.
How to cite: Maute, A., Matsuo, T., Rupani, V., Lien, C.-P., and Stolle, C.: Improving E-region Neutral Wind Variability in Numerical Models Using LEO Magnetometer Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9173, https://doi.org/10.5194/egusphere-egu26-9173, 2026.
Accurate estimation of thermosphere mass density and horizontal winds from satellite accelerometer measurements is crucial for understanding the environment experienced by low-Earth-orbit satellites. A critical step in this process is removing non-aerodynamic forces, such as radiation pressure, from calibrated accelerometer data. However, uncertainties in surface reflection and absorption coefficients, as well as incomplete thermal property information and calibration parameters for the accelerometer, often limit the accuracy of modeling. Therefore, this study presents a method for jointly optimizing radiation pressure parameters and accelerometer scale factors in the cross-track and radial direction and demonstrates their impact on wind observations.
During initial studies, the acceleration residuals (the difference between modeled and measured acceleration) in the cross-track direction exhibited a geographical pattern correlated with the magnetic field for both GRACE-A and GRACE-B. However, the residual is opposite in sign for both satellites in the orbital frame. As the satellites are in nearly the same orbit, with an along-track distance separation of only approximately 220km, this cannot be attributed to a vector-based force. The root cause has not yet been identified but could possibly be attributed to an instrument issue. However, it can be empirically corrected in the cross-track accelerometer measurements using quadratic functions of the magnetic vector components.
To isolate radiation pressure as much as possible during the optimization, we use GRACE data from 2009, a period when radiation pressure dominated over aerodynamic drag due to the low solar activity. Following the optimization, a significant reduction in residuals was observed for both GRACE-A and GRACE-B, despite the coefficients being tuned using only GRACE-A data. Including the magnetic correction increased consistency between GRACE-A and GRACE-B. Overall, the method achieved RMS reductions in unmodeled accelerations of more than 13% in the cross-track direction and 32% in the radial direction, indicating improved accuracy of the radiation pressure model.
Using the proposed radiation pressure model, we demonstrated increased consistency in observed crosswinds between GRACE-A and GRACE-B during periods of higher thermosphere mass density. The proposed approach is generalizable to future missions and improves neutral density and crosswind estimation from precise accelerometer measurements, thereby supporting space weather monitoring and forecasting efforts in the thermosphere.
How to cite: Jacobs, F., van den IJssel, J., and Siemes, C.: Optimizing Radiation Pressure Modeling for Improved Thermospheric Density and Wind Estimation from GRACE Accelerometer Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3761, https://doi.org/10.5194/egusphere-egu26-3761, 2026.
Sub-orbital flights of research rockets provide unique opportunities for science by access to near-Earth space. In the MAPHEUS program of DLR (German Aerospace Center) such flights are conducted for the main purpose of micro-gravity experiments (almost free of residual force). On Nov 11th, 2024 at 7h38 UTC MAPHEUS-15 was launched from Esrange space port (Sweden) to send a scientific payload to about 7 minutes of micro-gravity. During the flight, the payload passed altitudes between 80 km and 310 km at a rather constant attitude with angular rate of change below 1° per second. We use these conditions to study the ionospheric E-layer that can form at altitudes of 90-120 km. E-layer remote sensing is challenging as its contributions are often masked by stronger contributions of F-layer above (250-400 km).
Passing the E-layer during the rocket flight will induce changes of Total Electron Content (TEC) for the specific GNSS satellite links. The payload on the MAPHEUS rocket included two different GNSS receiver setups that recorded GNSS data: a navigation receiver (Septentrio AsteRx-m3 Pro+) and remote sensing receiver (based on a Syntony GNSS bit-grabber). A geometry-free linear combination is applied to dual-frequency GNSS phase observations in order to retrieve uncalibrated TEC. The retrieved TEC is geo-referenced with a GNSS-based trajectory of the payload. Phase wind-up effects have to be considered and corrected using attitude data from the on-board inertial navigation system. Unfortunately, radio interference limits the number of useful GNSS links: three Galileo satellites provide TEC results (L1-L5 combination) and four GPS satellite (L2-L5 combination).
In parallel to the rocket flight, the near-by EISCAT UHF incoherent scatter radar in Tromsø, Norway was used to measure the ionospheric electron density over Northern Scandinavia. These data and the Neustrelitz Electron Density Model (NEDM) allow to retrieve ancillary TEC. The comparison shows good agreement. Standard deviation of residuals between ancillary TEC and GNSS rocket results are in most cases below 1 TECU.
Profiles of TEC rate and TEC gradient are determined along the up-leg of the rocket flight for the low noise Galileo observations (L1-L5 combination). These profiles resolve significant anomalies at E-layer altitudes (90-120 km) that indicate the presence of an E-layer in the local ionosphere above Northern Scandinavia. The climatological data of NEDM underestimates the E-layer presence. However, the comparison with TEC derivates from the EISCAT measurements validate the E-layer presence.
How to cite: Semmling, M., Dreißigacker, C., Markgraf, M., Stienne, G., Badia, P., Kallenbach, A., Günzkofer, F., Ulich, T., Hoque, M., and Voigtmann, T.: TEC Retrieval from Sub-orbital Rocket Flight Data for Ionospheric E-layer Detection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12899, https://doi.org/10.5194/egusphere-egu26-12899, 2026.
Equatorial electrodynamic processes in the ionosphere are inherently complex and highly variable, particularly during super geomagnetic storms. And accurate 3-D imaging of ionospheric variations and their temporal evolution remains a longstanding challenge in space weather research. At 2100 UT on May 11, 2024, multi-scale electron density variations were observed by Swarm A/C satellites over Australia. On one hand, Swarm observations revealed prominent conjugate electron density enhancements, which was a phenomenon seldom reported in the early morning hours. On the other hand, observations from the Tianmu GNSS radio occultation (RO) indicated that the ionospheric F-region in the conjugate Southern Hemisphere was uplifted by more than 80 km over Australia and provided the evidence of the co-existence of equatorial plasma bubbles (EPBs). To better understand the physical mechanisms of these structures, we reconstructed their three-dimensional electron density distribution with NEDAM for the first time. The results reveal field-aligned characteristics in the enhancements. This suggests the presence of a dawn-side equatorial ionization anomaly (EIA). Using Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) simulations, we further demonstrated that the formation of a dawn‐side EIA can be driven by the disturbance dynamo electric field. The co‐existence of the dawn‐side EIA and embedded EPBs gave rise to the observed multi‐peak electron density structures.
How to cite: Li, L.: Multi-observation and Data Assimilation Analysis of 3-D Ionospheric Electron Density Variations During the Recovery Phase of the Gannon Storm , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8823, https://doi.org/10.5194/egusphere-egu26-8823, 2026.
The Rate of Total Electron Content (TEC) Index (ROTI) is widely used as an indicator of small-scale ionospheric irregularities and GNSS signal disturbance risk. Unlike Vertical Total Electron Content (VTEC), ROTI reflects rapid spatio-temporal variability and is linked to degraded positioning performance. However, ROTI values estimated from ground-based GNSS are spatially sparse and unevenly distributed, limiting their use for global monitoring.
In this study, we investigate data-driven methods for spatio-temporal interpolation of sparse-observation ROTI values. We make use of the global International GNSS Service (IGS) station network with more than 400 stations to calculate a ROTI dataset using all available GPS satellites. Gaussian Processes (GPs), Neural Processes (NPs) and Neural Networks (NNs) are evaluated in controlled data gap scenarios, where entire regions are held out to mimic poorly covered areas. Performance is assessed in terms of interpolation accuracy, capturing the dynamic nature of ROTI. For the evaluation we also focus on the higher ROTI values that may be linked to degradation in GNSS positioning quality. By systematically comparing these kernel-based methods and neural approaches, we analyze their strengths and limitations in representing ROTI. Based on these results, we aim to identify a robust strategy for generating continuous ROTI products that complement existing global ionospheric maps and support GNSS reliability monitoring.
How to cite: Iten, M. and Soja, B.: Comparing Gaussian Processes, Neural Processes and Neural Networks for Interpolation of Ionospheric ROTI, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3786, https://doi.org/10.5194/egusphere-egu26-3786, 2026.
The Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometry (CARIOQA) Pathfinder Mission aims at demonstrating a quantum accelerometer onboard a dedicated satellite mission with a launch date in the early 2030s. This Pathfinder Mission will raise the maturity of key technologies of an atom interferometer to TRL 8 to enable the deployment of a quantum accelerometer onboard a satellite gravimetry mission. While the primary mission objectives are related to characterization of the quantum accelerometer in an environment representative of a satellite gravimetry mission in terms of expected signal, several secondary mission objectives utilising the data collected in orbit are foreseen.
The Pathfinder Mission is currently in Phase B (CARIOQA-PHB), in which the preliminary mission concept, architecture and critical technology maturity plan will be developed in more detail based on the concluded Phase A. The Phase B is also accompanied by scientific studies evaluating the mission concept with respect to the realisation of primary and secondary mission objectives.
In this presentation we will focus on the application of the quantum accelerometer data for the determination of parameters of the upper atmosphere, e.g. density. The Pathfinder Mission will gather data in low Earth orbit where comparable accelerometer observations are sparse. The mission data can be used to improve atmospheric drag models. However, the study of Pathfinder Mission performance also relies on such models. We will give an overview of atmospheric drag in the context of the mission objectives and comparable datasets which can be used to augment the mission studies. We will also present the simulation strategy and results for atmospheric density determination based on the current Phase B status.
CARIOQA-PHB is a joint European project, funded by the European Union (id: 101189541), including experts in satellite instrument development (TAS, Exail SAS, ZARM, LEONARDO), quantum sensing (LUH, LTE, LP2N, ONERA, FORTH), space geodesy, Earth sciences and users of gravity field data (LUH, TUM, POLIMI), mission analysis (GMV) as well as in impact maximisation and assessment (PRAXI Network/FORTH, G.A.C. Group), coordinated by the French and German space agencies CNES and DLR under CNES lead.
How to cite: Schilling, M., Biskupek, L., Weigelt, M., Bremer, S., and Leipner, A.: CARIOQA Pathfinder Mission accelerometer applications, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9118, https://doi.org/10.5194/egusphere-egu26-9118, 2026.
The peak of the F2 layer in the ionosphere is a crucial anchor point in many electron density modeling methods. It is essential to predict the peak of the F2 layer accurately in order to create reliable models of the ionosphere. Recently, machine learning approaches have shown excellent results in predicting electron density, often surpassing the traditional empirical models of the ionosphere in terms of accuracy.
In this presentation, we analyze the neural network-based model of electron density in the topside ionosphere (NET) and optimize the hyperparameters of NET's submodels for NmF2 and hmF2. The dataset used in this study consists of radio occultation (RO) observations from the CHAMP, GRACE, and COSMIC-1 satellite missions from 2001 to 2019. The inputs to the submodels include geomagnetic latitude and longitude, universal time, day of the year, and the P10.7, Kp, and SYM/H indices. The tuned parameters in the hyperparameter optimization (HPO) were the sizes of each of the three hidden layers, activation function, dropout rate, standard deviation of the regularizing Gaussian noise layers, orders of the Fourier features (FFT) for periodic inputs, necessary number of Kp index observations, learning rate, and batch size.
We analyze the effects of regularization on the performance of both submodels, and find the optimal values that balance the bias-variance tradeoff. We also perform the feature selection and show that the history of the Kp index of up to 15 hours is important for reproducing the ionospheric behavior, which is in line with known physical evolution of the ionosphere during geomagnetic storms. The optimized models reproduce the effects of several physical processes, including complex dynamics driven by neutral winds and electromagnetic drifts. We showcase physical features depicted by the NET model and interpret them in combination with in-situ measurements of the plasma drifts.
How to cite: Laitinen, L., Smirnov, A., Kallio, E., and Prol, F. S.: Optimizing the neural network modeling of ionospheric F2-peak parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11224, https://doi.org/10.5194/egusphere-egu26-11224, 2026.
The ionosphere is the layer of the Earth’s upper atmosphere containing free electrons, where solar radiation ionizes atoms and affects GNSS signals. Airborne GNSS campaigns offer a unique opportunity to monitor ionospheric variations. This study presents a comprehensive analysis of Total Electron Content (TEC) using data acquired during the GEOHALO Mission over Italy and adjacent parts of the Mediterranean Sea. The dataset consists of GNSS observations collected by the HALO (High Altitude Long Range) research aircraft during flights conducted on 6th, 8th, 11th and 12th June 2012, at an approximate altitude of 3500 metres over sea areas.
The methodology is based on RINEX data extracted from binary receiver data (JAVAD GNSS) using RTKLIB. The GOPI Tool, a free software for the retrieval of TEC using dual-frequency GNSS data is used to estimate preliminary Slant TEC (STEC) and Vertical TEC (VTEC). However, GOPI assumes static position which is not sufficient for geo-referencing airborne results. Therefore, an additional processing step is introduced to compute Ionospheric Piercing Points (IPP) along the aircraft trajectory. A geometric ray tracing is applied to determine the IPP for the aircraft’s position assuming an ionospheric shell (~350km, F-layer). The analysis gives spatially referenced profiles of STEC and VTEC, for corresponding IPP along the flight trajectory.
Preliminary results confirm the expected enhancement of STEC at lower elevation angles and local maximum of VTEC is observed in the early afternoon on 8th,11th and 12th June 2012. However, in further steps, these results need to be validated, for example, using TEC Maps or the Neustrelitz Electron Density Model (NEDM).
How to cite: Gohel, M. V., Semmling, M., Moreno, M., Hoque, M., Wickert, J., and Förste, C.: Retrieval of Total Electron Content from Airborne GNSS Data recorded during the GEOHALO mission over the Mediterranean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11832, https://doi.org/10.5194/egusphere-egu26-11832, 2026.
Space Weather covers phenomena resulting from the Sun-Earth connection that can have detrimental effects on the operation of technological systems and human activities. The sun is currently in the solar maximum and therefore the access to the key information on space weather conditions becomes very important for precision and safety of life applications that use satellite signals.
Within the scope of the WeGA (Space Weather services for precise GNSS Applications) project funded by the Ministry of State Mecklenburg-Vorpommern, Germany, we have developed several new products and services, describing and monitoring ionospheric state and dynamics. The ionosphere is recognized as a major error source for operations of Global Navigation Satellite Systems (GNSS). A new ionospheric model called Neustrelitz Total electron Content Model for Galileo (NTCM-G), developed by the German Aerospace Centre, has been recently adopted by the European Commission for correcting the ionospheric delay of Galileo satellite signals. As a new product NTCM-G parameters will be updated in near real time using a globally distributed GNSS receiver network. GNSS satellites broadcast ionospheric correction parameters to improve GNSS operations. However, such corrections can only mitigate 50-70% of ionospheric errors. The actual error budgets for such corrections will be computed in near real time as new products. Ionospheric perturbations can degrade the accuracy, continuity, availability, and integrity of GNSS applications. In addition, two new products representing the actual spatial gradients and temporal variations of the ionosphere will be developed and made available via DLR’s Ionosphere Monitoring and Prediction Center (IMPC, https://impc.dlr.de/) to warn GNSS users about enhanced space weather impacts.
The new products will be evaluated by GNSS users and services in Mecklenburg-Vorpommern such as the SAPOS (Satellite Positioning Service of the German National Surveying), BSH (Federal Maritime and Hydrographic Agency) and Hochschule Neubrandenburg.
How to cite: Hoque, M. M., Semmling, M., Jakowski, N., Cahuasqui, A., Dühnen, H., Moreno, M., Nykiel, G., David, P., and Tagargouste, Y.: Space weather products for precise GNSS applications developed in the WeGA project, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12939, https://doi.org/10.5194/egusphere-egu26-12939, 2026.
Post-sunset equatorial plasma bubble (EPB) occurrences in the African sector are investigated using Global Navigation Satellite System (GNSS) radio occultation (RO) observations acquired by the FormoSat-7/Constellation Observing System for Meteorology, Ionosphere, and Climate-2 (COSMIC-2) mission. A subset of the global COSMIC-2 GNSS RO database, containing EPB events identified during the period 2023, is analyzed. The analysis is restricted to RO observations located within the African longitude sector (20°W – 40°E) and within ±20° geomagnetic latitude of the magnetic equator. EPB events are identified using complete L1-band amplitude scintillation index (S4) profiles derived from RO signal-to-noise ratio measurements. An EPB event is defined when the maximum S4 value exceeds 0.3 at F-region altitudes. Only complete RO observations, for which the sampling spatial scale is smaller than the first Fresnel zone, are considered. To focus on post-sunset ionospheric irregularities, the analysis is further restricted to observations occurring within the local time interval between 18:00 and 24:00 local time (LT). The analyzed COSMIC-2 RO observations show that EPB occurrence rates in the African sector increase rapidly after local sunset and reach a maximum during the early post-sunset period. The highest occurrence rates are observed between approximately 19:00 and 22:00 LT, after which EPB occurrences decrease toward later nighttime hours. The latitudinal distribution of detected EPBs is mainly confined within ±20° geomagnetic latitude and exhibits a near-symmetric pattern with respect to the magnetic equator. Seasonal differences in EPB occurrence are also observed, with higher occurrence rates during equinoctial periods and relatively lower occurrence rates during solstitial seasons. COSMIC-2 RO profiles associated with EPB events also show pronounced reductions in F-region electron density, accompanied by enhanced L1-band S4 values during the post-sunset period.
How to cite: Olabode, A., Alizadeh, M., Tsai, L.-C., and Schuh, H.: Post-Sunset Equatorial Plasma Bubble Occurrence in the African Sector Observed by COSMIC-2 Radio Occultation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16350, https://doi.org/10.5194/egusphere-egu26-16350, 2026.
GNSS Radio Occultation (GNSS-RO) provides globally distributed bending angle observations that improve numerical weather prediction and climate monitoring. Accurate neutral atmosphere retrieval requires removing ionospheric effects from RO bending angles, commonly via the standard dual-frequency linear combination of L1 and L2 bending angles. While this approach mitigates first-order ionospheric effects, a residual ionospheric error (RIE) remains due to frequency-dependent ray-path separation within complex ionospheric structures, leading to systematic biases in stratosphere and mesosphere products.
Previous research demonstrated RIEs are proportional to the squared difference between the L1 and L2 bending angles, scaled by a coefficient, called kappa, providing the basis for the kappa correction framework [1]. Subsequent studies improved its practical performance by characterizing the dependence of kappa on geophysical parameters (e.g., solar activity, local time, solar zenith angle, geomagnetic latitude) and incorporating these trends into enhanced parameterizations [2,3]. Under the assumption of a symmetric ionosphere, RIE tends to be predominantly negative, and the kappa correction can reduce the resulting negative bias. However, robust accuracy improvements remain challenging under widely varying electron densities across diverse geographic regions. Under a strongly asymmetric ionosphere—where the RIE can become positive—a kappa correction fails to reduce, or even amplify, the error. This limitation motivates a deep-learning-based correction that adapts to complex, geographic-dependent ionospheric structures.
This study develops a physics-guided neural network (PGNN) to correct RIE by learning the residual error relative to a physics-based baseline (i.e., the kappa correction) using geophysical parameters [4]. Training labels are generated from ray-tracing simulations through an ionosphere-only environment modeled by NeQuick-3D. The proposed architecture incorporates a feature-wise attention gate that adaptively weights the input variables. This method enables the model to capture condition-dependent ionospheric structures that are poorly represented by fixed-form kappa parameterizations, particularly under strong ionospheric asymmetry during high solar activity.
For validation, we compare our model against a kappa correction baseline, a purely data-driven neural network, and a transformer-based PGNN on an independent test set. Across diverse geographic regions, the proposed PGNN with feature-wise attention consistently achieves the best agreement with the true RIE, yielding a highest correlation coefficient of 0.935 and a lowest RMSE of 6.398 nrad. These results indicate that combining a kappa-based physical prior with attention-guided residual learning provides a robust correction across geographic regions.
References
[1] Healy, S. B., & Culverwell, I. D. (2015). A modification to the standard ionospheric correction method used in GPS radio occultation. Atmospheric Measurement Techniques, 8(8), 3385–3393.https://doi.org/10.5194/amt-8-3385-2015
[2] Angling, M. J., Elvidge S., & Healy, S. B. (2018). Improved model for correcting the ionospheric impact on bending angle in radio occultation measurements. Atmospheric Measurement Techniques, 11(4), 2213–2224.https://doi.org/10.5194/amt-11-2213-2018
[3] Park, J., Chang, J., Sun, K., & Lee, J. (2025). Residual ionospheric error correction in GNSS radio occultation bending angles: parametric analysis using electron density profiles derived from COSMIC-II data. EGU General Assembly 2025, EGU25-18658. https://doi.org/10.5194/egusphere-egu25-18658
[4] Daw, A., Watkins, W., Read, J., Karpatne, A., & Kumar, V. (2021). Physics-guided Neural Networks (PGNN): An Application in Lake Temperature Modeling. arXiv preprint arXiv:1710.11431. https://doi.org/10.48550/arXiv.1710.11431
How to cite: Park, J., Chang, J., Park, J., and Lee, J.: Correcting GNSS Radio Occultation Residual Ionospheric Errors using Attention-Based Physics-Guided Neural Networks in Various Geographic Regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17444, https://doi.org/10.5194/egusphere-egu26-17444, 2026.
Accelerometer measurements are essential for accurate gravity field recovery and for the extraction of thermospheric density used in drag estimation. The GRACE-C accelerometer is among the few instruments currently providing measurements of sufficient accuracy for these applications. With the advent of a new generation of gravity missions, it is increasingly important to characterise non-gravitational disturbances in order to identify additional phenomena that may affect accelerometer observations. This study analyses the 10 Hz accelerometer measurements from GRACE-C, which represent the highest-cadence dataset available to date. We investigate the characteristic signal signatures associated with terminator crossings, field-aligned currents, and geomagnetic storms under both low and high solar activity conditions. The aim is to improve the understanding of how space weather processes influence accelerometer measurements and, consequently, gravity field determination and thermospheric densities retrieval.
How to cite: Tzamali, M. and Pagiatakis, S.: Space weather signatures in accelerometer measurements of GRACE-FO C: Insights from 10 Hz measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17626, https://doi.org/10.5194/egusphere-egu26-17626, 2026.
In recent years, with the launch of numerous Low Earth Orbit (LEO) satellites, GNSS observation data used for precise orbit determination can be utilized for topside ionosphere sounding. This study integrates topside GNSS observations from LEO satellites, including the Chinese Tianmu-1 satellite constellation and COSMIC-2, with ground-based GNSS observations to jointly establish a global double-layer ionospheric model. The model employs spherical harmonic functions to fit the observations, with the two layers set at altitudes of 450 km and 1200 km, respectively, and a temporal resolution of one hour. During the modeling process, ground-based GNSS observations contribute to both the bottom and top layers, while GNSS observations from LEO satellites contribute exclusively to the top layer. To validate the model's performance, data from three months (February, May, and August 2024) during a period of high solar activity were used. The validation involved comparing the model outputs with slant total electron content (STEC) observations from over 500 global GNSS stations and vertical total electron content (VTEC) data from six ocean altimetry satellites. The results indicate that the proposed double-layer ionospheric product achieves high accuracy, outperforming traditional single-layer ionospheric models.
How to cite: Chen, P.: A Method for Establishing a Global Double-Layer Ionosphere Model Using GNSS Observations from LEO Satellites for Orbit Determination, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17671, https://doi.org/10.5194/egusphere-egu26-17671, 2026.
Since its launch by the VLBI group at TU Wien in 2008, the Vienna VLBI and Satellite Software VieVS has grown considerably. What began as pure VLBI analysis software has evolved into a powerful conglomerate of various modules. The VLBI capabilities include a tool for simulating raw telescope data and the VLBI core module, with observation data simulation, analysis of source and satellite observations, and global solution options. The previously integrated scheduling tool was separated from VieVS-VLBI and further developed as a full-fledged standalone scheduling and simulation software, VieSched++, which is currently maintained at ETH Zurich. In addition to the VLBI-related modules, VieVS offers a tropospheric ray-tracing package called RADIATE. Another highlight is the independent open-source software package raPPPid for Precise Point Positioning, which enables the processing of low-cost or high-quality GNSS observations in highly adaptable PPP approaches. In this contribution, we provide an overview of all current open-source components of VieVS and give a preview of two new modules that will be publicly available in the future. These are VieCompy, a stand-alone combination software for estimating global parameters based on normal equations, and VieSOFT, a tool for correcting source structure at fringe-fitting level, which can also be used for correcting VLBI observations to the Genesis satellite.
How to cite: Böhm, S., Böhm, J., Gruber, J., Jaron, F., Kern, L., Krásná, H., Schartner, M., Urban, P., Wareyka-Glaner, M. F., and Wolf, H.: The Vienna VLBI and Satellite Software VieVS: Status and Roadmap, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17126, https://doi.org/10.5194/egusphere-egu26-17126, 2026.
How to cite: Schartner, M., McCallum, L., and Soja, B.: VGOS observing strategy for 2026, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17583, https://doi.org/10.5194/egusphere-egu26-17583, 2026.
Satellite observation is becoming more and more relevant to geodetic VLBI since the Genesis is coming up. The Genesis satellite will carry a VLBI transmitter emitting broadband signals in S, C and X bands. A mode with a PRN code is proposed to enable single station measurements. We explore the potential of such measurement by analyzing real data. In the experiment ASO304, the Australian VGOS telescopes tracked five GPS satellites using their L band capability. We correlate these data with a GNSS-like approach — correlating with local replicas instead of interferometry. We perform systematic analysis on the obtained delays to characterize potential performance and error sources, in preparation for the assessment of single station operation possibility of the Genesis mission.
How to cite: Deleu, T., Cheng, Y., Karatekin, O., and Ozyildirim, A.: Single station experiments with ASO304 data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17739, https://doi.org/10.5194/egusphere-egu26-17739, 2026.
The International Terrestrial Reference Frame (ITRF) serves as the foundation for applications in navigation and Earth sciences. It is computed and released by the International Earth Rotation and Reference Systems Service (IERS) and is a combination of the solution time series of four space geodetic techniques: Global Navigation Satellite System (GNSS), Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI). The latest release, ITRF2020 and its updates, does not yet achieve the Global Geodetic Observing System (GGOS) goal of 1 mm accuracy and 0.1 mm/yr stability.
One of the major accuracy-limiting factors when combining the four techniques are systematic differences between the techniques. With the aim of improving the combination by reducting these systematics, the combination of clock parameters of different instruments referenced to one common stable clock at one site can be considered. We present an approach that introduces a common time frame for both techniques. Therefore, the definition of the reference clock is of the utmost importance. We realize a mean stable reference clock (MSRC), defined as the mean of the clock estimates of all stable clocks (H-masers). This significantly reduces variations in the reference clock and thus minimizes its impact on the estimated station clock parameters. We discuss first results of a combination of VLBI and GNSS clock parameters performed on a basic level, by introducing GNSS clock estimates as a priori values in the VLBI analysis.
A unified clock parameterization is required when combining different space geodetic techniques considering clock parameters. Until now, each technique uses its own parametrization. In the current GNSS strategy, clock parameters are estimated epoch-wise with a high temporal resolution of 5 minutes, whereas the VLBI strategy uses session-wise clock offset, drift, and quadratic terms, along with 1-hourly piecewise linear continuous clock parameters. We discuss initial concepts for the homogenization of the clock parameterization for VLBI and GNSS on normal equation level.
How to cite: Klug, J., Seitz, M., Reinhold, A., Glaser, S., Widczisk, J., and Männel, B.: Using clock parameters for the combination of GNSS and VLBI, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10387, https://doi.org/10.5194/egusphere-egu26-10387, 2026.
The Caspian Sea represents a major component of continental water storage and a key target for geodetic monitoring of mass redistribution. This contribution analyses Caspian Sea level (CSL) variability over 2003–2024 using a combination of satellite gravimetry (GRACE/GRACE-FO) and satellite altimetry.
GRACE-derived water mass estimates were corrected for signal leakage and steric effects, improving consistency with independent altimetric observations. The resulting time series was analysed using wavelet decomposition to separate periodic components and extract the underlying trend. Change-point analysis applied to the reconstructed trend reveals four successive linear phases: a rise of 6.66 cm yr-1 (Jan 2003–Feb 2006), a long decline of −9.99 cm yr-1 (Feb 2006–Aug 2016), a weaker decline of −3.32 cm yr-1 (Aug 2016–May 2019), and a strongly accelerated drop of −23.18 cm yr-1 (May 2019–Dec 2024).
The relationship between CSL and hydroclimatic forcing was examined using difference integral curves and wavelet coherence with precipitation, evaporation and river runoff. At the annual scale, CSL and runoff are nearly in phase. At interannual scales, the dominant control varies over time. From 2003 to 2016, runoff variability closely follows CSL changes. Between 2016 and 2019, increased runoff partly offset decreasing precipitation and increasing evaporation, consistent with the temporary slowdown in CSL decline. Since 2019, the combined effect of reduced precipitation, intensified evaporation and declining runoff explains the recent acceleration in CSL drop.
Acknowledgements: This work was primarily supported by the Spanish national project PID2021-122142OB-I00 (MCIN/AEI/10.13039/501100011033), and additionally by the ThinkInAzul Programme (Generalitat Valenciana, GVA-THINKINAZUL/2021/035) and the EU Horizon Europe project SEA4FUTURE (Grant Agreement No. 101212647).
How to cite: Wang, M., Vigo Aguiar, M. I., García García, D., and Vargas Alemañy, J. A.: Integrated gravimetry–altimetry analysis of Caspian Sea level variability (2003–2024), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14088, https://doi.org/10.5194/egusphere-egu26-14088, 2026.
In land vehicle-borne dynamic strapdown gravimetry, horizontal accelerometer biases project onto the navigation frame through the time-varying heading angle, producing systematic errors in gravity disturbance estimation. Due to the inherent heading instability of ground vehicles, these bias-induced errors exhibit low-frequency, continuous, and heading-correlated characteristics along the survey line. The conventional forward-backward fusion method exploits the mirror symmetry of repeated lines to cancel such errors, but at the cost of halving the effective survey coverage and precluding single-pass operation.
To overcome this limitation, this study proposes a MLP-based (multilayer perceptron) compensation approach that directly learns the mapping from vehicle motion states to the systematic gravity estimation error. The input features include the forward-only gravity disturbance (east and north), heading representation (sine and cosine of yaw), speed, and yaw rate. The supervision target is defined as the residual between the forward-only solution and the forward-backward fused reference, which inherently encodes the heading-dependent bias effect. A compact two-hidden-layer MLP (32 neurons each, ReLU activation) is trained with mean squared error loss and early stopping.
Experiments on a vehicle-borne gravimetry dataset (4782 samples, 70%/30% sequential split) show that the proposed method reduces the east-component RMSE from 1.188 mGal to 0.188 mGal (84.1% improvement) and the north-component RMSE from 0.478 mGal to 0.134 mGal (72.1% improvement). The compensated results closely approximate the fused reference, confirming that the MLP effectively learns the slowly varying and heading-correlated error characteristics.
How to cite: Feng, H., Guo, Y., Yu, R., Cao, J., Xiong, Z., Luo, K., Cai, S., and Wu, M.: MLP-based Error Compensation Method for Single-Direction Survey Lines in Land Vehicle Strapdown Gravimetry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15687, https://doi.org/10.5194/egusphere-egu26-15687, 2026.
The Atomic Clock Ensemble in Space (ACES) was launched to the International Space Station (ISS) on 21st of April of this year. Following successful installation on the external payload facility of the Columbus module, the commissioning phase began, which will approximately last until the end of 2025. ACES brought two time transfer methods into orbit: the Microwave Link (MWL) and the European Laser Timing (ELT) link. These two links differ not only in frequency, – one operates in the microwave domain, the other in the optical domain – but also in their detection principle. In this contribution, we introduce the optical pulsed time transfer experiment ELT and compare its measurement principle with that of MWL.
Just like T2L2, ELT is a combination of Satellite Laser Ranging (SLR) and a one-way ranging measurement, in which the laser pulses are time tagged in the ACES timescale. Contrary to T2L2, the complexity of the measurement is not in the space segment but on ground. Although the entire SLR ground segment is available in principle, restrictions exist for ranging to the ISS and the availability of a stable clock signal at these geodetic stations.
The Wettzell Laser Ranging System (WLRS) located at the Geodetic Observatory Wettzell in Germany is the main ground station for the ELT experiment. We describe the steps taken at WLRS to participate in the ELT experiment and the available hardware. We then present the ACES payload and the ELT Data Center, which is responsible for the data processing chain. We highlight the challenges of the data processing based on the first synchronisation measurements between Wettzell and the ACES time scale. Finally, we discuss the objectives of ELT and the benefit optical time transfer will bring for space geodesy and how it fits to the objectives of GGOS.
How to cite: Schlicht, A. and the ACES Team: ELT: Time transfer by laser pulses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19282, https://doi.org/10.5194/egusphere-egu26-19282, 2026.
