The central pillar of my research are the GRACE and GRACE-FO satellite missions. These missions provide a unique opportunity to observe spatial and temporal variations in the Earth’s gravity field. These variations reflect large-scale mass redistributions, which are dominated by water mass transport across continents, oceans, and ice sheets. Consequently, GRACE and its successor mission, GRACE-FO, enable global monitoring of changes in terrestrial water storage (TWS), integrating all water components from surface water over soil moisture, snow and ice, down to groundwater.

In this talk, I will take you on a journey from global observations of the Earth’s gravity field to physically interpretable data products over land and oceans, and demonstrate how these products can be applied in hydrological research.

Global gravity field solutions are typically delivered as spherical harmonic coefficients, a mathematical representation that is not directly accessible to most users. I will show how we transform this complex information into intuitive, user-friendly gridded datasets, including robust uncertainty estimates, an aspect crucial for many practical applications. I will also highlight the importance of such accessible data products for open science initiatives and public data platforms, including the Copernicus Climate Change Service.

Finally, I will present several case studies illustrating the use of TWS data in hydrology. These include the quantification of the ongoing Central European drought that began in 2018, as well as investigations into the interplay between climate change, natural variability, and human influence in the East African Rift region. I will also demonstrate the added value of combining TWS observations with complementary remote sensing datasets to assess global changes in groundwater storage.

How to cite: Boergens, E.: From Observations of the Earth’s Gravity Field to Insights into Hydrology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3354, https://doi.org/10.5194/egusphere-egu26-3354, 2026.

Since the time of Kepler, Newton, and Huygens in the 17th century, geodesy has been concerned with determining the Earth’s figure, orientation, and gravitational field. The dawn of the space age in 1957 gave rise to a new branch of the discipline: satellite geodesy. It was only through the use of satellites that geodesy truly became a global science - oceans ceased to be barriers, and the Earth could be observed and measured as an integrated whole using consistent datasets. Particular attention was devoted to resolving the spatial structure of the Earth’s gravity field and, eventually, its temporal variations. Knowledge of the gravity field forms a natural link to the study of the Earth’s interior, the circulation of the oceans, and, more recently, the climate system. Today, changes in the gravity field provide key insights into climate change, including ice mass loss in Greenland and Antarctica, sea-level rise, and broader changes in the global water cycle. These advances have only been possible through the use of highly sophisticated gravity-field satellites, a field known as satellite gravimetry.

During the first four decades of space exploration, satellite gravimetry relied primarily on analyzing the orbital motion of satellites. Due to the uneven global distribution of tracking stations, initially limited measurement accuracy, and shortcomings in early analysis models, reconstructing global models of the Earth’s gravity field posed a major challenge. A decisive breakthrough came in the final decade of the 20th century with the transition from passive satellites to missions equipped with dedicated, high-precision instrumentation for gravity-field determination. The Vening Meinesz lecture will review the historical background of satellite gravimetry as well as mission objectives, measurement principles and implementation challenges of modern gravity missions like CHAMP, GRACE, GOCE, and GRACE-FO. It will further highlight selected scientific results and applications from these missions and outline opportunities for the next generation of geodesists arising from future gravity field missions currently under development.

Further reading: Frank Flechtner, Christoph Reigber, Reiner Rummel, and Georges Balmino (2021): Satellite Gravimetry: A Review of Its Realization, Surveys in Geophysics, 42:1029–1074, https://doi.org/10.1007/s10712-021-09658-0

How to cite: Flechtner, F.: Satellite Gravimetry: Realization and Further Prospects, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9119, https://doi.org/10.5194/egusphere-egu26-9119, 2026.

North-central Chile is a highly seismically active region. While the last megathrust earthquake occurred in 1730, the area has also experienced large events in recent decades, such as the 2015 Illapel earthquake (Mw 8.3), as well as numerous seismic sequences and persistent swarms. Although these phenomena are widespread along the Chilean subduction margin, their dynamics and potential connection to major earthquakes remain poorly understood. 

Within this framework, the ABYSS project has deployed Distributed Acoustic Sensing (DAS) interrogators along offshore telecommunication fiber-optic cables, complemented by temporary and permanent onshore seismic stations. This configuration offers a unique opportunity to monitor and investigate the offshore microseismicity in a region characterized by sparse permanent instrumentation and the absence of previous offshore sensors.

In this study, we develop a workflow to precisely relocate the seismicity recorded by the ABYSS network. We combine the probabilistic, non-linear hypocentral inversion using NonLinLoc with double-difference relocation using HypoDD, incorporating a 3D P- and S-wave velocity model and differential times derived from waveform cross-correlation on both DAS and onshore stations. Through this integrated approach, we identify and analyze clusters of seismicity associated with swarm activity and short-term seismic sequences. In particular, we apply the workflow to episodes such as the Tongoy swarm initiated on 30 December 2024, whose largest event reached Ml 5.3, and the offshore Ovalle sequence that occurred between October and November 2025.

Our goal is to precisely characterize these sequences by improving constraints on the geometry and spatio-temporal evolution, gaining insights into the processes driving this activity, and shedding light on how present-day swarm dynamics may relate to the occurrence of larger earthquakes along the Chilean subduction margin.

How to cite: Peralta, T., Flores, M. C., Rivet, D., Potin, B., Baillet, M., and Ruiz, S.: High-resolution relocation of seismic swarms using offshore DAS and onshore seismic data in north-central Chile, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-887, https://doi.org/10.5194/egusphere-egu26-887, 2026.

Numerical simulations of earthquake cycles provide essential insights into fault mechanics and the physical interpretation of frictional parameters. Here, we utilize a spring-block system governed by rate-and-state friction to systematically compare earthquake cycle behaviors under quasi-dynamic and fully dynamic conditions. Our simulations demonstrate that for both approaches, the static stress drop, dynamic stress drop, and peak stress scale linearly with the logarithm of the loading rate [ln(Vpl/V0)]; however, the scaling coefficients are distinct and are modulated by both frictional parameters and the system stiffness. Specifically, we observe stress overshoot during the coseismic phase in dynamic models, contrasting with the undershoot observed in quasi-dynamic simulations. Additionally, parameter sweeps reveal that stress drops decrease as the stiffness ratio kc/k increases. This study highlights the importance of the inertial term effect in interpreting earthquake cycle behaviors.

How to cite: Chai, L. and Hu, F.: Scaling of Stress Drop with Rate-and-State Frictional Parameters in Spring-Block Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6568, https://doi.org/10.5194/egusphere-egu26-6568, 2026.

Collision and relentless underthrusting of India beneath Eurasia resulted in large-scale deformation of the Indian lithosphere. Anisotropic parameters serve as a good proxies to decipher deformation in such complex orogenic collision zones. In this study, we present anisotropy characteristics of the crust beneath Sikkim Himalaya using harmonic decomposition of P-to-S converted phases identified in P-wave receiver functions (P-RFs). Analysis of azimuthal variation of these phases enabled parameterizing the crustal anisotropic properties, with depth. Initially, 11,087 high quality P-RFs were computed using waveforms of teleseismic earthquakes having magnitude  ≥ 5.5 and signal to noise ratio  ≥ 2.5 within an epicentral distance range of 30° - 100°, recorded at a network of 38 seismic stations deployed in Sikkim Himalaya and the adjoining foreland basin. Analysis of the first three harmonic degrees (i.e. k= 0, 1 and 2) reveals that the upper crustal anisotropy is oriented WSW-ENE to E-W, coinciding well with the trends of crustal microcracks and fractures. The mid to lower crustal anisotropy aligns predominantly with the dipping decollement layer along which the Indian plate is underthrusting Tibet. An orthogonal reorientation is observed within the extent of the Dhubri-Chungthang Fault Zone authenticating its role in segmenting the orogen. The lower crustal anisotropy is highly perturbed signifying a highly heterogeneous nature of the Moho.  Existence of multiple layers of anisotropy possessing distinct geometries varying with depth could be an indication of a highly complex deformational regime resulting from active crustal shortening.

How to cite: Kumar, G., Singh, A., Singh, C., Saikia, D., and Kumar, M. R.: Crustal Seismic anisotropy in Sikkim Himalaya: Implications for deformation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10972, https://doi.org/10.5194/egusphere-egu26-10972, 2026.

Regular monitoring of small to moderate sources of continuous earthquake events in the complex tectonics of Himalayan region helps in clearly defining the ongoing seismotectonic process. The study of moment tensor inversion to decipher the fault planes responsible for current seismic activity in the Kishtwar region of Northwest part of Himalaya has been undertaken by establishing a six-station network in 2022 and among them 15 events of shallow origin with magnitude ranging from M_L ~ 3.0 to 4.0 occurred in the local region of seismic network are used for the moment tensor inversion. A few number of studies didn’t able to clearly demarcate the actual scenario of seismotectonics in the northwest part of Himalaya due to its difficult terrain and complex geology. This area has been studied for fault plane solution by a software package ISOLA based on MATLAB programming environment. The source inversion is performed via iterative deconvolution method and synthetic seismogram is generated through green’s function computation via discrete wavenumber method using the regional crustal velocity model. However, the inversion is performed at several trial source position and at various frequency bands based on the epicenter distance and the magnitude of earthquake to find the best solution resulting from the maximum correlation between the recorded and synthetically generated waveforms. A 2D space-time grid search is performed for determining the optimal time and positon of earthquake generation. Perhaps calculating source parameters such as moment magnitude, centroid depth and fault parameters equally with describing uncertainty quantities such as variance reduction factor and condition number will deliver the reliability and stability to the solution. A strong follow-up uncertainty quantification can justify the best estimated fault plane solution. Quality of earthquake event can be calculated through their DC and CLVD percentage and maximum & minimum compression stress direction. Focal mechanism solution of these events following thrust with strike-slip focal mechanism and represents the compressional regime in north-northeastern direction. The centroid depth obtained by moment tensor inversion of all events falls within the depth zone of Main Himalayan Thrust (MHT) suggesting seismicity is concentrated along the major detachment in the region.

How to cite: Tiwari, S. and Gupta, S. C.: Moment tensor analysis and uncertainty quantification of local earthquake events: tectonic implication in the northwestern Himalayan region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13656, https://doi.org/10.5194/egusphere-egu26-13656, 2026.

With the popularization of dense seismic array observations, tomographic imaging of subsurface velocity structures using surface wave dispersion data extracted via subarray partitioning has emerged as a new trend. The primary advantages of subarray-based dispersion data extraction lie in its reduced susceptibility to the inhomogeneous distribution of noise sources, which yields more stable and reliable dispersion measurements. Additionally, this approach enhances the energy of higher-order modes, thereby providing tighter constraints on subsurface velocity structures. Compared with the higher-order modes of Rayleigh waves, both the fundamental and higher-order modes of Love waves exhibit simpler dispersion characteristics with fewer mode crossings and overlaps, making them more favorable for joint inversion to constrain subsurface SH-wave velocity structures.

Traditional subarray surface wave imaging methods (e.g., SSWI) typically perform 1D velocity structure inversion at individual locations first, followed by stitching all 1D models to generate pseudo-2D or 3D velocity models. Despite its simplicity and computational efficiency, this direct stitching strategy is highly vulnerable to uneven station distributions, and the resultant velocity models may suffer from artificial velocity jumps. To address these limitations, Luo & Yao (2025) proposed a direct subarray surface wave imaging method (SSWDI), which eliminates the stitching step inherent in traditional methods and incorporates spatial smoothness constraints on velocity structures, thus enabling more robust inversion of subarray-derived dispersion data for subsurface imaging. However, the SSWDI method originally focused exclusively on the fundamental mode of Rayleigh waves. In this study, we further extend the SSWDI framework to accommodate both fundamental and higher-order modes of Love waves, and validate the improved method using both numerical synthetic data and field observational data.

Reference

Luo, S., and H. Yao (2025), Direct Tomography of S-wave Structure Using Subarray Surface Wave Dispersion Data: Methodology and Validation, Geophysics, 1–60, doi:10.1190/geo-2024-0515.

How to cite: Luo, S.: 3D SH-wave Velocity Tomography via Direct Inversion of Multimode Love Wave Dispersion Curves from Seismic Subarrays, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16937, https://doi.org/10.5194/egusphere-egu26-16937, 2026.

Seismic hazard assessment is crucial for the design of critical facilities, whose damage could lead to severe consequences. The design of such facilities typically requires the definition of seismic actions associated with recurrence periods on the order of 5,000-10,000 years. Earthquakes with such low frequencies are well documented in highly deforming regions, where paleoseismic records commonly encompass several seismic cycles of active faults. In contrast, in slow-deforming regions or areas of low seismicity, the scarcity of seismic data hinders the definition of seismogenic zones. In this context, geological studies of active seismogenic faults are essential, as they allow the characterisation of seismic behaviour over time spans far exceeding those covered by instrumental or historical records. These data can contribute to constraining fault’s seismic cycles and estimating earthquake magnitude–frequency distributions at the fault scale.

Despite their importance, the incorporation of faults into seismic hazard models remains challenging, particularly in low strain regions such as the western margin of the Valencia Trough. This region of the NE of Iberia (from the Vallès-Penedès Graben to the Valencia Depression) corresponds to a passive margin characterised by a basin-and-range structure, bounded by multiple NNE–SSW-oriented normal faults formed during the Neogene rifting episode. Those faults are usually associated with mountain fronts, although our recent studies have found some new faults crosscutting Pleistocene alluvial fans. These newly discovered faults are being studied by means of geomorphology, geophysics, paleoseismology and geochronology in order to estimate their seismic parameters. Several challenges arise when analysing these faults, including fault identification, incomplete geological records, and the need for complex dating techniques.

Moreover, in regions characterised by fault systems, fault interactions may play a significant role. In regions such as the studied area, these interactions may result in long quiescent periods followed by phases of increased activity or even cascading events. Under such conditions, distinguishing between quiescent and active phases is especially difficult, as recurrence intervals are expected to span several thousands of years in both cases.

In this work, we explore existing methodologies for the computation of seismic hazard incorporating geological data from faults and fault systems in slow-deforming regions, using the western margin of the Valencia Trough as a case study. To this end, a detailed geometric characterization of the fault system is carried out to establish the geometric relationships among faults. Recent morphotectonic analyses and newly acquired geological data are then used to constrain the seismic parameters of the studied faults and to estimate their earthquake frequency distributions. Finally, several alternative seismic source models are proposed, forming the basis for the construction of a logic tree for subsequent seismic hazard calculations. These
models, although in progress, provide a framework for improving seismic hazard assessments in slow-deforming regions, contributing to safer design of critical infrastructure.

How to cite: Ollé-López, M., García-Mayordomo, J., Scotti, O., and Masana, E.: A seismogenic modelling approach for rift-basin fault systems in slow-deforming regions: application to the western margin of the Valencia Trough, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20741, https://doi.org/10.5194/egusphere-egu26-20741, 2026.

The 2015 Mw 7.8 Gorkha earthquake was followed by numerous aftershocks that provided important information on active faulting in central Nepal. Accurate moment tensor estimations are essential for determining the source parameters of these seismic events. In this study, we determine double-couple and full moment tensor solutions for selected aftershocks of the 2015 Nepal earthquake sequence using a regional 1D velocity model.

The waveform data recorded by the temporary broadband network (NAMASTE) are used to analyse 51 aftershocks with M > 3.5. A library of Green’s functions is computed using the frequency–wavenumber method based on a 1D velocity model of the Nepal region. Synthetic waveforms derived from the Green’s functions are used to invert the waveform data for moment tensor estimation. Both body waves and surface waves are used in the inversion, and they contribute separately to the moment tensor solutions. The analysis focuses on regional waveforms in relatively higher frequency ranges.

Both double-couple–constrained and full moment tensor inversions are performed, and the resulting source parameters are examined in terms of waveform fit, centroid depth, and fault-plane orientation. This work presents a set of moment tensor solutions for the 2015 Nepal aftershocks using a 1D regional velocity model and provides a reference for future studies using more complex velocity structures.

How to cite: Lahon, P., Silwal, V., and Mahanta, R.: Double-Couple and Full Moment Tensor Solutions of the 2015 Nepal Aftershocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21099, https://doi.org/10.5194/egusphere-egu26-21099, 2026.

The alternative proxy parameters for seismic site amplification beyond the conventional time-averaged shear wave velocity of the upper 30 m (V_S,30) are investigated in this study with a focus on quantities that can be derived or constrained from surface wave-based measurements such as Spectral Analysis of Surface Waves (SASW) and Continuous Surface Wave System (CSWS) testing. Surface wave methods provide dispersion curves that are inverted to obtain near-surface shear wave velocity profiles, which are then used to construct synthetic one-dimensional layered models for ground response analysis. For each profile, two different candidate site parameters are evaluated, including V_S,30 and the impedance ratio between the surface layer and the underlying half-space. These parameters are chosen to reflect what can realistically be inferred from SASW/CSWS-derived velocity profiles, particularly the shallow stiffness and impedance contrasts that strongly influence amplification. Correlation analyses are carried out to quantify how well each parameter explains the variability in amplification across the synthetic suite. The results are used to assess whether the impedance ratio provides stronger or more consistent correlation with amplification than V_S,30, thereby offering guidance on how surface wave–based site characterization can be better integrated into proxy-based amplification and site classification schemes in seismic design practice.

How to cite: Singh, V. and Baidya, D. K.: Evaluating SASW/CSWS-Derived Proxies for Seismic Site Amplification, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21425, https://doi.org/10.5194/egusphere-egu26-21425, 2026.

The Rif’s belt is characterized by low to moderate seismic activity resulting from the continental collision between the African and Eurasian plates. This seismic activity, which involves devastation and human losses, requires an in-depth study of its origins and mechanisms. This study aims to identify the geological structures responsible for seismic activity in the eastern Rif by adopting an integrated methodological approach. The methodology relies on the use of a Geographic Information System (GIS) to process and analyze multiple geological, seismological, and geophysical datasets. Various filters were applied to magnetic and gravimetric data (vertical derivatives) to characterize the subsurface. The analysis of earthquake focal mechanisms helped identify active faults. The results show that the seismicity, with a NW-SE orientation, is localized within a fragile depression south of the city of Selouane. The final geological model highlights a system of faults and strike-slips oriented NE-SW and NW-SE. A significant spatial correlation is observed between epicenters and Messinian-aged NW-SE strike-slips, suggesting their reactivation. The analysis indicates that a system of dextral strike-slips is likely the source of this seismic activity. The proposed geodynamic model represents a major advancement in understanding local seismic activities and serves as an essential reference for future studies. These results significantly contribute to the assessment and management of seismic risks, thereby enhancing the safety and resilience of populations in this high-risk area.

KEYWORDS: Geodynamic model; Seismotectonic; Focal mechanism; Magnetic; Gravimetric; ·
Eastern Rif. 

How to cite: Iken, H., Nouayti, A., Nouayti, N., and Khattach, D.: An integrated geodynamic analysis of seismic sources in the Eastern Rif: Insights from geological, seismological, gravimetric, and aeromagnetic data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22669, https://doi.org/10.5194/egusphere-egu26-22669, 2026.

Current demand for critical metals including Cu is outstripping current supply and will further escalate in the future. A significant source of Cu comes from porphyry deposits, which contribute to >60% of global Cu ore production. Many of these porphyry Cu deposits are found along convergent margins such as the Andes and the Sunda-Banda arc in Indonesia and these same arcs also host highly active volcanoes. Understanding the magmatic and geodynamic factors that contribute towards priming magmas for Cu fertility as opposed to volcanic eruptions can aid in identification of prospective targets for exploration.

Here we present analyses of apatite populations from known porphyry Cu deposits and active volcanoes along the Sunda-Banda arc in Indonesia. To gain a complete overview of the mineral associations and their information, we incorporate textural information to analyze both apatite inclusions and their mineral hosts, such as pyroxenes and amphiboles, as well as groundmass apatite. These mineral compositions will serve as input for thermodynamic models to constrain the volatile chemistry and budget, as well as the volatile saturation depths. The information gathered will be combined to test our working hypotheses that the magmas with high Cu fertility store at distinct depths, have geochemical signatures that suggest deep fractionation of garnet and amphibole, and are associated with anomalous geodynamic features such as slab tears.

Our ongoing work advances current understanding on magma storage and transfer along and across fertile magmatic arcs, aiming to better understand magmatic pre-conditioning for porphyry copper deposit formation to complement exploration efforts to find copper deposits in the geological records.

How to cite: Utami, S. B., Ubide, T., Rosenbaum, G., Li, W., Handini, E., Wood, S., Handley, H., and Goode, L.: Insights into the copper accumulation potential of magmas along the Sunda-Banda arc, Indonesia from apatite and its mineral hosts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-938, https://doi.org/10.5194/egusphere-egu26-938, 2026.

Abstract:

Strike-slip basement faults and their related segments are crucial for oil and gas exploration. These faults are considered favorable channels for hydrocarbon migration. The multistage activities of these faults influence the development of hydrocarbon-bearing structures. They can also produce fracture systems that enhance reservoir properties and boost oil and gas production. Understanding how strike-slip fault segments and their associated structures affect hydrocarbon accumulation is essential for geological research and exploration planning. This study aims to characterize the geometry and structural evolution of the strike-slip basement fault with Pan-African or Arabian trends, investigate the relationship between fault segments, and assess their impact on the distribution of hydrocarbon traps. This research focuses on the structural and tectono-sedimentary analyses of the Kazerun fault system based on processing and interpretation of the surface data (e.g., satellite images and aeromagnetic data) and the subsurface data (e.g., 2D and 3D seismic and well data) in the Zagros orogenic belt, SW Iran. The relationship between the segmented strike-slip fault zone and hydrocarbon reservoirs is analyzed through map view patterns and profile features. Results reveal that the Arabian-trending Kazerun fault system comprises segmented dextral strike-slip faults and is considered a transform and wrench fault. These faults display various planar configurations, including linear, en-echelon, horsetail splays, and irregular geometries in the map view. Based on the seismic data interpretation, three structural styles develop along the Kazerun strike-slip fault zone, including vertical or oblique, pull-apart (negative flower structure), and push-up (positive flower structure) segments. Releasing and restraining bends and oversteps formed at the tail end of the Kazerun strike-slip fault segments. In the study area, salt diapirism occurred along the pull-apart segment and the releasing bend. Hydrocarbon traps are developed in the push-up segment and the restraining bend. Fractures are less prominent in the vertical segments but more developed in push-up and pull-apart segments, which act as pathways for fluid migration and improving reservoir quality. The push-up segment and restraining bend exhibit a higher degree of branching fractures, making them the most significant for reservoir development. This research shows that strike-slip fault segmentation (in the form of fault overlapping or stepping) and their lateral linkage control the reservoir distribution and connectivity. Recognizing the growth and lateral connections of strike-slip fault segments is crucial for structural analysis and predicting fault-controlled reservoirs. These findings offer valuable insights into the structural characteristics of strike-slip fault zones and can enhance oil and gas exploration in the Zagros fold-and-thrust belt and other similar regions.

Keywords:

Strike-slip basement fault, Segmentation pattern, Oil/Gas fields, Zagros orogenic belt, SW Iran

How to cite: Soleimany, B., Tajmir Riahi, Z., Payrovian, G. R., and Sepahvand, S.: Impact of segmentation pattern of the Pan-African trending strike-slip basement fault on the spatial distribution of hydrocarbon traps in SW Iran, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1377, https://doi.org/10.5194/egusphere-egu26-1377, 2026.

Skarn-type Cu–Fe–Au mineralization in the Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is closely associated with Early Cretaceous intermediate to felsic magmatism; however, the links between magmatic evolution and ore-forming efficiency remain poorly constrained. In the Tonglushan ore field, one of the largest Cu–Fe–Au skarn systems in eastern China, multiple intrusive phases are spatially distributed, providing an ideal opportunity to investigate how magmatic processes control metallogenic potential. Here we present new geochronological and geochemical constraints on quartz monzodiorite porphyry, quartz monzodiorite, quartz diorite, and their mafic microgranular enclaves (MMEs) from different sectors of the Tonglushan ore field.

Zircon U–Pb ages indicate synchronous emplacement of all intrusive phases and MMEs at ca. 142–140 Ma. Whole-rock geochemistry and Sr–Nd–Hf isotopes indicate that these intrusive rocks belong to a high-K calc-alkaline to weakly adakitic series and were derived from an enriched lithospheric mantle source modified by slab-derived components, followed by extensive fractional crystallization. The MMEs record efficient mixing between mafic and felsic magmas, highlighting the role of mafic recharge in supplying heat and metal components to the evolving system. Estimates of magmatic water contents and oxygen fugacity from zircon compositions reveal systematic variations among different intrusions. The Jiguanzui and Tonglushan quartz monzodiorite porphyries are characterized by high water contents and elevated oxidation states, consistent with intense Cu–Au and Cu–Fe–Au mineralization, whereas the weakly mineralized Zhengjiawan quartz diorite exhibits lower values. These observations suggest that, beyond structural controls, the metallogenic fertility of intrusions in the Tonglushan ore field was primarily governed by fractional crystallization, mafic magma input, and the development of highly hydrous and oxidized magmatic systems.

Our study demonstrates that integrated whole-rock and zircon geochemical indicators provide effective tools for evaluating the ore-forming potential of skarn-type Cu–Fe–Au mineralization related intrusions in the MLYRB.

How to cite: Zhang, M. and Tan, J.: Magmatic controls on skarn-type Cu–Fe–Au mineralization in the Tonglushan ore field, Middle–Lower Yangtze River Metallogenic Belt, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2162, https://doi.org/10.5194/egusphere-egu26-2162, 2026.

Low-temperature thermochronology provides key constraints on the post-mineralization exhumation and preservation of orogenic gold deposits. In this study, we investigate the exhumation histories of the Anjiayingzi and Jinchanggouliang gold deposits, located respectively in the Kalaqin metamorphic core complex (MCC) and the Nuluerhu magmatic dome within the Chifeng–Chaoyang metallogenic belt on the northern margin of the North China Craton.

Both deposits formed in the Early Cretaceous (~130 Ma), but at significantly different depths (5.6–7.1 km for Anjiayingzi and 1.0–2.6 km for Jinchanggouliang), and are currently exposed at the surface, implying differential post-mineralization exhumation. Zircon and apatite (U–Th)/He and fission-track analyses were conducted on ore-hosting rocks to reconstruct cooling and exhumation histories. Combined age–elevation relationships and thermal history modeling reveal that the Anjiayingzi deposit experienced multi-stage, rapid exhumation totaling ~6.75 km since mineralization, with the most intense exhumation occurring between 130 and 80 Ma. In contrast, the Jinchanggouliang deposit underwent slower and more limited exhumation, with a total exhumation of ~2.50 km over the same period.

The contrasting exhumation histories coincide with an Early Cretaceous regional extensional regime affecting the northern margin of the North China Craton. We suggest that tectonic setting plays a first-order role in controlling post-mineralization exhumation. Deposits hosted within MCCs are characterized by rapid extensional denudation related to detachment faulting, whereas deposits hosted in magmatic domes are mainly exhumed through regional uplift and surface erosion. These results emphasize the importance of structural architecture in governing the exhumation, preservation, and exposure of gold deposits in extensional orogenic systems.

How to cite: Li, A. and Fu, L.: Post-mineralization exhumation of gold deposits on the northern margin of the North China Craton: constraints from low-temperature thermochronology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2243, https://doi.org/10.5194/egusphere-egu26-2243, 2026.

The Southeast Anatolian Suture Belt hosts the oceanic and continental remnants of the southern Neotethyan realm. During the Late Cretaceous, the southern Neotethyan domain experienced an Andean-type magmatism on its northern continental margin (the Tauride-Anatolide Platform), characterized by the Baskil Magmatics. The plutonic part of this unit is intruded by numerous dikes, which are the primary focus of this study. The U-Pb zircon dating of the dikes and their granodioritic host rocks indicates that their emplacement occurred within a narrow interval, between 81-79 Ma. The dikes vary chemically from basalt to dacite, while the host rocks range from andesitic to dacitic. On the normal mid-ocean ridge (N-MORB)-normalized plots, all samples exhibit negative Nb anomalies. Trace element systematics reveals that this dike system is chemically heterogeneous, consisting of five distinct chemical types. The elemental and isotope ratios indicate varying contributions from depleted and enriched components. All chemical types, with relative Nb depletion, suggest incorporation of slab-derived and/or crustal additions. This interpretation is further supported by the EM-2-like Pb isotopic ratios. Based on the variability in elemental and isotopic composition, this intrusive system appears highly heterogeneous, likely due to the combined effects of mantle source, crustal contamination, and fractional crystallization. The bulk geochemical characteristics of the studied dikes and their host rocks suggest that these intrusives formed at a continental arc. Considering the available paleontological and geochronological age data, it appears that the intraoceanic subduction and continental arc magmatism in the Southern Neotethys occurred simultaneously; the former created the Yüksekova arc-basin system, whereas the latter formed the Baskil Arc.

Note: This study was supported by project Fübap-MF.15.12.

How to cite: Ural, M., Sayit, K., Koralay, E., and Göncüoglu, M. C.: Geochemical and Geochronological approaches of Baskil Dikes (Elazığ, Eastern Turkey): Discrimination between the Late Cretaceous Continental and Oceanic Arc-related Magmatism in the Southern Neotethys, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2274, https://doi.org/10.5194/egusphere-egu26-2274, 2026.

The Kaladgi Basin, an E–W trending intracratonic basin in the northern part of the Dharwar Craton, preserves favourable structural and stratigraphic conditions for sandstone-hosted and unconformity-related U–REE mineralization. In the study area, the Neoproterozoic Cave Temple Arenite (CTA) of the Badami Group unconformably overlies deformed Mesoproterozoic rocks of the Bagalkot Group. The crystalline basement of the Kaladgi Supergroup comprises Meso- to Neoarchaean Peninsular Gneiss and the Chitradurga Greenstone Belt. This association of cratonic basement, schist belt, and basin-margin fault and fold systems provides an excellent structural framework for hydrothermal fluid circulation and mineralization.

Detailed thematic mapping at 1:25,000 scale in the Ramdurg–Suriban sector reveals that NNW–SSE–oriented Dharwarian stress generated a series of anticlines and synclines involving the Saundatti Quartzite, Malaprabha Phyllite, and Yaragatti Argillite, as constrained by conjugate fracture analysis and S–C fabric development. An E–W trending tectonic fault defines the contact between the Peninsular Gneissic Complex and Saundatti Quartzite, with comparable faulted contacts also developed within the Bagalkot Group. Intense faulting resulted in silicification, chalcedonic brecciation, and pervasive hydrothermal alteration along these contact zones. Transverse normal faults with associated brecciation accommodate strain related to the main E–W structure and indicate episodic reactivation of the basin architecture.

Fusion ICP–MS analysis of 20 bedrock samples collected proximal to these fault zones shows U₂₃₈ concentrations exceeding twice the threshold values of National Geochemical Mapping (NGCM) stream sediment sample. Uranium enrichment is spatially associated with Malaprabha Phyllite, first-cycle CTA, and silicified banded hematite quartzite veins of the Hiriyur Formation. Chondrite-normalized (La/Yb)_n versus (Eu/Eu*)_n systematics indicates a dominantly low-temperature basinal brine hydrothermal system characterized by low (La/Yb)_n <25 and negative Eu anomalies. Redox-sensitive (Ce/Ce*)_n versus (Eu/Eu*)_n plots further indicate reducing fluid conditions. In contrast, quartz–chlorite veins developed within sheared Malaprabha Phyllite and younger dolerite record comparatively higher-temperature fluids, marked by Eu²⁺ mobilization ((Eu/Eu*)_n > 0.8) and negative Ce anomalies. These results suggest that reactivated, structure-controlled tectonites acted as effective fluid pathways, with the TTG-dominated Peninsular Gneissic Complex serving as a likely uranium source and contributing to localized U–REE mineralization along the basin margin.

How to cite: Mahanandia, A., Lal, M. M., Singh, T. G., Nandhagopal, N., and Singh, S.: Structure-controlled Uranium + REE mineralization in low temperature basinal brine hydrothermal system at the contact of Kaladgi Basin and Peninsular Gneissic Complex, South India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2923, https://doi.org/10.5194/egusphere-egu26-2923, 2026.

Gravity observations are widely used in volcanic monitoring to infer subsurface mass redistributions, commonly interpreted in terms of magma intrusion. However, gravity changes may also arise from thermo-poro-elastic (TPE) processes associated with temperature and pore-pressure variations in fluid-saturated reservoirs. Neglecting these effects can lead to ambiguous or misleading interpretations of gravity signals during volcanic unrest.

The recent development of TPE inclusion models allows us to describe the mechanical fields induced by fluid-saturated rock volumes undergoing pore-pressure and temperature variations. These sources can coexist with magmatic sources within volcanic systems and are typically located at shallower depths than the deep magmatic reservoir, which acts as the primary engine by releasing hot fluids. These exsolved fluids rise from depth and either accumulate in, or migrate through, overlying brittle rock volumes, which respond to thermal and pore-pressure perturbations and therefore act as secondary sources of deformation and gravity change. In this work, we consider a disk-shaped TPE inclusion, a geometry that has been successfully applied in previous studies to represent deformation fields that are predominantly radial and associated with axisymmetric sources.

The results show that gravity variations induced by a TPE inclusion depend strongly on the fluid phase. Both liquid water and gaseous fluids can produce the same significant ground uplift, but lead to different gravity residuals: negative for liquid water and minor but positive for gaseous fluids. In contrast, condensation or vaporization of a thin layer near the surface can generate large gravity changes without notable deformation. As a result, heating and pressurization of a TPE inclusion can mask or weaken the gravitational signature of magma ascent, complicating the interpretation of gravity data and highlighting the need to account for hydrothermal effects when estimating magma volumes during unrest.

Gravity data collected over the past decades at the Campi Flegrei caldera (Italy) provide an ideal test site for applying our model and offer intriguing insights into both past and current unrest phases, although our results are applicable to any volcanic system with an active hydrothermal system. These findings highlight the importance of incorporating TPE effects into gravity data interpretation and integrated volcano monitoring strategies. Accounting for them improves our ability to distinguish between magmatic and hydrothermal contributions, leading to more robust assessments of subsurface dynamics and volcanic hazards.

How to cite: Nespoli, M., Bonafede, M., and Belardinelli, M. E.: Thermo-Poro-Elastic effects as hidden drivers of gravity signals in volcanic systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3001, https://doi.org/10.5194/egusphere-egu26-3001, 2026.

Abstract: Unlike ionosphere, troposphere is nondispersive and delays cannot be determined from observations of signals at different radio frequencies. In GNSS data processing, station height, receiver clock error and tropospheric delay are highly correlated to each other, especially in kinematic situations. Although zenith hydrostatic delay can be provided with sufficient accuracy, zenith wet delay, which is more spatially and temporally varying than hydrostatic component, has to be carefully processed. Usually, temporal dependence of tropospheric delays at zenith is modeled as a random walk process with a solely given process noise rate σ_rw in GNSS processing. The usually used σ_rw is a constant throughout whole process session and is in range of 3~10 mm per sqrt hour. This setting is generally appropriate for desirable GNSS positioning estimation in normal conditions. However, modeling zenith tropospheric delay by using a constant σ_rw in whole session will be unsatisfactory in cases of special weather conditions, e.g., the shower case. The σ_rw is a measure of magnitude of typical variation of zenith path delay or its residual after calibration in a given time. Values of σ_rw that are too large could weaken strength for geodetic estimation, while values that are too small may introduce systematic errors, since a strong constraint for tropospheric unknowns is imposed to stabilize the system. The random walk model for wet delay must be constrained approximately to "correct" value to obtain optimum parameters estimates. Assuming temporal change of tropospheric delay at an arbitrary station can be described by random walk model, the process noise levels were calculated by some scholars. They employed water vapor radiometric, surface meteorological measurements and numerical weather model data set for optimum selection of σ_rw. In general, although a lot of efforts have made to optimize post-processing and/or real-time GNSS tropospheric delay estimation, stochastic modeling of zenith wet delay remains insufficiently investigated, especially for kinematic applications. Since temporal variation of zenith wet delay depends on water vapor content in atmosphere, it seems to be reasonable that constraints should be geographically and/or time dependent. In this work, we first investigate sensitivity of both station coordinates and zenith wet delay estimators on different σ_rw values, and then try to propose to take benefit from post-processed static or kinematic estimated tropospheric delay to obtain the optimum σ_rw. The general objective is that if zenith tropospheric delays are of different variation characteristic, e.g., relatively stable or rapid changing, then a varying σ_rw, e.g., small or large value, could be employed, which should be more theoretically feasible compared with a invariant σ_rw. The initial results show that the new method can efficiently obtain epoch-wise σ_rw values at different stations. Compared to results from conventional constant σ_rw value, time-varying noise rate can improve precision of PPP solutions. We note that this first results represent performance view at several selected stations, more works should be done to draw global or even long-term conclusions.

This work is supported by National Natural Science Foundation of China (42304010), Youth Foundation of Changzhou Institute of Technology (YN21046).

How to cite: Wang, M., Lu, B., and Zhong, Q.: The initial results about optimum the random walk process noise rate for GNSS tropospheric delay estimation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4327, https://doi.org/10.5194/egusphere-egu26-4327, 2026.

The Yanshan-Liaoning metallogenic belt (YLMB), the second-largest molybdenum deposit cluster in China, hosts over twenty porphyry molybdenum deposits, including the large-scale Caosiyao, Sadaigoumen, and Dasuji deposits, as well as the newly discovered medium- to large-scale Qiandongdamiao, Zhujiawa, and Taipingcun deposits. Geochronological data indicate that the duration of molybdenum mineralization spanned ca. 100 Myrs, from the Triassic to Early Cretaceous (240–140 Ma). However, the reasons for such a prolonged or multi-period metallogenic event, and the magmatic and geodynamic processes controlling the spatial–temporal distribution of these deposits, remain poorly understood.

Here we summarize the geological, chronological and geochemical data from selected molybdenum deposit to reconstruct the temporal–spatial distribution and tectonic setting of ore- metallogenic history in the YLMB. The formation of molybdenum deposit in the YLMB can be divided into three periods of 240–220 Ma, 185–180 Ma and 160–140 Ma. The ore-forming intrusions among these three periods illustrate an overall characteristic that metaluminous to peraluminous, high-K calc-alkalic to shoshonite series acidic rocks, and the source of intrusions is the Archaean–Paleoproterozoic lower crust. Through in-depth analysis of Sr-Nd-Hf isotopic data, we find that the magma source that during the 185-180 Ma stage is relatively younger, mainly reflecting the partial melting of Paleoproterozoic crust, whereas the magma source that during the 240–220 Ma and 160–140 Ma stages likely are contained both from the Paleoproterozoic and Neoarchean crust. Further calculations using trace element content ratios reveal a shallower magma source along the magma evolution during the 240–220 Ma period, which supported by the gradual decrease trend in crustal thickness. In contrast, the calculation of crustal thickness during the 185–180 Ma and 160–140 Ma stages show an increase trend, suggested an thicken process in the depth of the magma source.

Spatially, the porphyry molybdenum deposits formed during these three periods exhibit distinct geographic distributions. Deposits formed at 240–220 Ma are mainly located in the northern part of the YLMB, including the Chengde-Zhangbei-Fengning district. Those formed at 185–180 Ma are primarily located in the Liaoxi district, eastern part of the YLMB while deposits formed at 160–140 Ma are located in the southern part of the YLMB, particularly in the Xinghe-Zhangjiakou-Xinglong district. We propose that the variations of the spatial–temporal distribution and geochemical characteristics of the molybdenum deposit formed during different periods in the YLMB are controlled by variations of their geodynamic settings. The porphyry molybdenum deposits formed in 240–220 Ma are under the post-collision or post-orogenic extension environment between the North China Plate and the Siberian Plate in the Middle Triassic. Deposits formed in 185–180 Ma are under the extension environment in the early stage of the Yanshanian movement, and porphyry molybdenum deposits formed in 160–140 Ma are in the strong extrusion environment in the main stage of the Yanshanian movement.

Our findings demonstrate the multi-period metallogenic history of the YLMB, highlighting the critical role of magma source, storage depth, and geodynamic setting in controlling the formation of porphyry molybdenum deposits.

How to cite: Jiang, C., Liu, Q., Cao, L., Li, A., and Fu, L.: Magmatic and geodynamic processes control on the formation of porphyry molybdenum deposits: Insights from the Yanshan-Liaoning metallogenic belt, northern margin of North China Craton, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4396, https://doi.org/10.5194/egusphere-egu26-4396, 2026.

Microcontinents are isolated fragments of continental crust surrounded by oceanic lithosphere. They commonly occur in modern ocean and are also recognized in orogenic system. They can be accreted onto continental margins through collision and subduction during ocean-continent subduction process, and lead to migration of subduction zone toward the oceanic side. However, it is not well understood whether and how this process can be recorded by metamorphism. In this study, a high grade metamorphic-magmatic terrane is recognized along the previously defined Qilian block. The Datong-Mengyuan terrane (DMT) is separated from the low-medium grade metamorphic basement of the Qilian block (QLB) by dextral strike-slip ductile shear zone and ophiolite mélange. The petrology and texturally-controlled U-Pb multi-mineral geochronology reveal that the mafic and felsic granulites from the DMT record two significance events of metamorphism. The earlier event experienced a pressure and temperature conditions of 11.4–13.7 kbar and 735–805°C at ca. 500 Ma, and later stage records a pressure and temperature conditions of 5.5–9.6 kbar and 790–840°C at ca. 460 Ma. We suggest that the earlier Cambrian high pressure granulite facies metamorphism is resulted from collision and thickening related to the accretion of the DMT to the Qilian block, and the later low-medium pressure granulite facies overprinting formed by decompression heating, which happened in continental arc setting and is associated with shift of subduction zone toward the ocean. These findings provide a critical example of metamorphic record on the microcontinent accretion and convergent plate boundary dynamics.

How to cite: Mao, X. and Zhang, J.: Metamorphism records microcontinent accretion and subduction relocation: an example from early Paleozoic Qilian Orogenic Belt, NW China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4872, https://doi.org/10.5194/egusphere-egu26-4872, 2026.

The distribution of rare gases within the Earth’s interior has caught the attention of scientists for the past few years. The inertness and volatility of noble gases make them excellent tracers for understanding the chemical evolution of Earth’s mantle and atmosphere. Previous studies indicate that noble gases can be found associated with clathrates, form their own oxides, or, in some cases, noble gases such as helium and xenon can even bond with Fe under extreme pressure (p) - temperature (T) conditions like those in Earth’s core. However, the ability of lower mantle mineral phases to house rare gases remains poorly understood, leaving important gaps in knowledge. Helium and argon are noble gases of interest in this study. The isotopes ⁴He and ⁴⁰Ar are produced from the radioactive decay of ²³⁸U and ⁴⁰K within the Earth’s interior, while ³He and ³⁶Ar are regarded as primordial, introduced during the accretion of Earth. Dong et al. (2022) revealed that noble gases can become reactive under mantle pressure conditions. Still, their ability to be incorporated into mantle minerals via adsorption needs to be thoroughly studied, as there are many limitations in the experiments conducted to measure the solubility of noble gases in minerals under mantle p-T conditions. In this study, we investigated the adsorption behavior of helium and argon on the (001) plane of periclase (MgO) by employing first-principles density functional theory (DFT) calculations.

Adsorption energies were estimated across pressures ranging from 0 to 125 GPa, representative of conditions throughout Earth’s interior, i.e., approximately up to the Core Mantle Boundary (CMB). At ambient pressure, both helium and argon showed negative adsorption energies, indicating stable adsorption relative to isolated species (MgO, Ar, He). These energies became increasingly negative with pressure, becoming notably negative beyond 75 GPa which corresponds to lower mantle pressures. This may be due to the accelerated reactivity of noble gases at extreme pressure conditions, as reported in previous studies. Additionally, under all pressure conditions argon exhibited stronger adsorption than helium, indicating enhanced argon retention in lower mantle conditions. However, further investigations into the mechanical and dynamical stability of these adsorbed structures are required to completely understand the mechanisms governing noble gas occurrence in the Earth’s lower mantle.

How to cite: Karangara, A. and Kumar Das, P.: Adsorption of Helium and Argon on the (001) Surface of Periclase: A First-Principles Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4988, https://doi.org/10.5194/egusphere-egu26-4988, 2026.

Soil CO₂ emission is a key proxy for investigating fluid migration processes associated with volcanic and tectonic activity. In particular, the analysis of the spatial distribution of geochemical anomalies represents an effective tool for identifying active structures and zones of ongoing deformation. Numerous studies have shown that faults and fracture systems play a fundamental role in controlling the localization and evolution of surface geochemical anomalies.

Vulcano Island (Aeolian Archipelago, Italy) is characterized by intense hydrothermal activity and persistent soil CO₂ emissions, providing a natural laboratory to investigate the relationships between fluid circulation and active tectonic structures. In this study, we present an integrated analysis of soil CO₂ fluxes based on results obtained from periodic surveys and continuous soil CO₂ flux records acquired at key sites across the island.

Periodic measurements are performed on fixed spatial grids, allowing the production of soil CO₂ flux maps and the identification of areas characterized by elevated degassing rates. At selected sites, the carbon isotopic composition of gases is analyzed to constrain gas sources.

These spatial datasets provide insights into the structural control exerted by the main tectonic lineaments on gas release at the surface. Continuous CO₂ flux monitoring enables the investigation of temporal variations and transient degassing signals potentially related to seismic and tectonic processes. In particular, the recent volcanic crisis at Vulcano Island, started on 2021, characterized by a marked increase in soil CO₂ flux, allowed a more detailed identification of preferential CO₂ emission pathways, highlighting zones of enhanced permeability associated with fault and fracture systems.

This work is carried out within the framework of the CAVEAT project (Central-southern Aeolian islands: Volcanism and tEArIng in the Tyrrhenian subduction system), which aims to provide a comprehensive understanding of the current geodynamics of the southern Tyrrhenian region.

How to cite: De Gregorio, S., Camarda, M., Capasso, G., Di Martino, R. M. R., Pisciotta, A., and Prano, V.: Soil CO₂ Emissions as Indicators of Fluid Pathways in Volcanic–Tectonic Environments: Insights from Vulcano Island, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5147, https://doi.org/10.5194/egusphere-egu26-5147, 2026.

Mg-bearing minerals, including brucite [Mg(OH)₂], lizardite [Mg₃(Si₂O₅)(OH)₄] and iowaite [Mg₆Fe³⁺₂(OH)₁₆Cl₂·4H₂O] are variably reactive with carbon dioxide (CO₂) at Earth’s surface conditions and can be used to mineralize and sequester this greenhouse gas. Here, we assess the impact of temperature (5, 20 and 40 °C) on the rate of CO₂ mineralization of these minerals. At each temperature, mineral powders (~100 mg ) were placed in a 7.5-litre flow-through reactor that was supplied with humidified laboratory air (0.042% CO₂; 100% RH) at ~200 mL/min. Subsamples (n = 54) of each mineral were collected over 3 months and analyzed (XRD, TIC, BET) to ascertain the amount and rate of carbonation as a function of time, temperature, and mineral feedstock.

Preliminary X-ray diffraction (XRD) results show the formation of dypingite [Mg₅(CO₃)₄(OH)₂·5H₂O] and a decrease in the abundance of brucite over time. The 003 peak of iowaite shifted to smaller d-spacings, indicating replacement of chloride by carbonate ions and a transition to a more pyroaurite-rich [Mg₆Fe³⁺₂(CO₃)(OH)₁₆·4H₂O] composition. Total Inorganic Carbon (TIC) measurements were used to determine the amount and rate of carbonation as a function of time, temperature, and mineralogy.

The results of this study will help us estimate the carbonation kinetics of these minerals in ultramafic ores and mine tailings under different temperature conditions relevant to large-scale deployment of CO₂ mineralization at mines across the globe.

How to cite: Sulemana, S. Z., Wilson, S., Moyo, A., Akhtar, S., Power, I. M., and Sleep, S.: Temperature-dependence of CO2 drawdown into Mg-bearing minerals., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6294, https://doi.org/10.5194/egusphere-egu26-6294, 2026.

The main focus of the study is to calibrate Sentinel-1 InSAR Line-of-Sight (LOS) velocities along a ~700 km North-South transect extending from the Black Sea coast (Kastamonu-Samsun) to the Mediterranean (Mersin-Gaziantep). This transect encompasses diverse tectonic regimes, including the North Anatolian Fault Zone, the Central Anatolian Block, and the junction of the East Anatolian Fault Zone. This complex structure of the transect requires detailed analysis of the GNSS-InSAR calibration procedure including validation. 

Across the study region, processed LiCSAR products are integrated with 3D velocities derived from the continuous local CORS network (21 stations) and an extensive campaign-based GNSS network (200 stations). For calibration, GNSS velocities are first projected into the satellite LOS geometry using LOS vectors derived from coherent InSAR pixels within a 1-km radius. The velocity bias (ΔVlos) is calculated at continuous GNSS locations. This correction surface is propagated using various conventional and Machine Learning techniques independently, including Kriging, Weighted Least Squares (WLS) based Quadratic Surface fitting, Thin Plate Spline (TPS) and Radial Basis Functions (Gaussian, Multiquadric, and Inverse Multiquadric). To address specific error sources, the contributions of topography-correlated atmospheric delays and local spatial trends are also analyzed by Geographically Weighted Regression (GWR) and Random Forest regression. Cross-validation is applied to assess the quality of each model individually where spatial random sampling and plate boundaries are also considered. This study presents preliminary results for obtaining a validated basis for generating up-to-date velocity fields over Türkiye.

How to cite: Elvanlı, M. and Durmaz, M.: Comparative Analysis of Machine Learning and Geostatistical Approaches for GNSS-InSAR Integration: A Case Study in Anatolia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7178, https://doi.org/10.5194/egusphere-egu26-7178, 2026.

Geomagnetic storms (GS) significantly perturb the near-Earth environment, leading to enhanced thermosphere density, increased non-conservative forces, and degraded satellite orbit determination, particularly for Doppler-based techniques such as DORIS. In this study, we investigate and improve DORIS orbit determination performance during GS conditions by developing storm-adapted processing strategies. Storm days were classified using geomagnetic indices and categorized into moderate to severe storm levels (G3-G5).

Four distinct processing strategies were implemented and evaluated: a standard operational solution and three experimental storm-adapted solutions, designed through systematic modifications of drag constraints and observation-elimination criteria. These strategies were tested through targeted daily and weekly experiments conducted across multiple DORIS-equipped satellites, with a particular emphasis on periods of intense storms.

The storm-adapted strategies demonstrate clear performance improvements relative to the standard solution during geomagnetic storms. The modified strategies reduce orbit residual RMS in all orbital components, improve Length-of-Day (LOD) variance by approximately 40-80%, and decrease LOD mean biases by nearly 60%. Additionally, Earth Rotation Parameters (ERP) exhibit notable improvements, with reductions of approximately 22–25% in both bias and variability for the polar motion components (X/Y pole). Among the tested configurations, the combined strategy, particularly when applied with zero-rotation constraints, consistently delivers the best performance during intense storm conditions (Kp ≥ 8+). These results demonstrate that storm-adapted DORIS processing strategies significantly enhance orbit and geophysical parameter estimation during disturbed space-weather conditions.

How to cite: Kumar, V., Stepanek, P., Filler, V., Balasubramanian, N., and Dikshit, O.: Impact of Storm-Adapted DORIS Processing on Orbit Quality and Earth Rotation Parameters During Geomagnetic Storms , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7764, https://doi.org/10.5194/egusphere-egu26-7764, 2026.

Abstract: The study of fluid inclusions and sulfur isotope characteristics of barite deposits is crucial for tracing the source of ore-forming materials and predicting prospecting targets. Current research indicate that the Sangmuchang barite deposit in northern Guizhou is primarily hosted within the joint fractures of dolomites in the Sinian Dengying Formation and Cambrian Qingxudong Formation. The contact between ore bodies and surrounding rocks is distinct, with the orebodies occurring as veins and lenticular. The ore textures are mainly veinlets, stockworks, massive, and banded, while the ore structures consist of inequigranular tabular-columnar blastic, fine-crystalline, and arenaceous texture.  Fluid inclusion studies reveal that  the inclusions are single-phase aqueous inclusions. Microthermometric measurements of 33 inclusions show that their homogenization temperatures range from 81°C to 182°C, with an average of 132°C; Salinity values vary from 9.61 wt.% NaCl eqv to 20.63 wt.% NaCl eqv, with an average of 17.53 wt.% NaCl eqv. Ten sulfur isotope analyses from the deposit show that the δ³⁴SV-CDT values range from 40.89‰ to 46.95‰, with a mean of +44.51‰.The characteristics of fluid inclusion salinity, temperature and sulfur isotopes suggest that the ore-forming fluids of this barite deposit are characterized by moderate-low temperature and moderate-high salinity. These ore-forming fluids were mainly derived from basin brines, with contributions from meteoric water. The significant enrichment of heavy sulfur isotopes and homogeneous sulfur isotope composition reveal that the sulfur source of ore-forming materials in this barite deposit is a relatively singular source for the sulfur in the ore-forming materials, which is similar to the δ³⁴S characteristics of Sinian marine evaporites, suggesting a close genetic relationship between the sulfur source and evaporites. Therefore, the Sangmuchang barite deposit is interpreted as a moderate-low temperature hydrothermal deposit.  It was formed by the migration of moderate -low temperature hydrothermal fluids in the sedimentary basin, which leached ore-forming materials from underlying and surrounding barium-rich evaporite sequences, followed by precipitation within structural fracture zones under the mixing of meteoric water. The structural fracture zones and areas indicative of fluid migration pathways along the basin margin are important targets for exploration prediction. Keywords: ore-forming fluid; fluid inclusion; sulfur isotope; barite; northern Guizhou

How to cite: Chen, Y., Wang, J., and Liu, Z.: Study on the Source of Ore-Forming Materials of the Sangmuchang Barite Deposit in Northern Guizhou, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8505, https://doi.org/10.5194/egusphere-egu26-8505, 2026.

Uranium is a strategically important metal with applications in nuclear energy, medicine, radiometric dating, food processing, industrial radiography, material sciences, and catalysis. This study presents a detailed microtextural and geochemical investigation of uranium mineralization from the Bodal uranium mine, Mohla-Manpur-Chowki, Central India. Uranium occurs as both crystalline and colloidal precipitates, with coffinite [U(SiO₄)_1-x(OH)_4x] and gummite representing the dominant uranium-bearing phases. The mineralization is spatially and genetically associated with altered metabasalts. Petrographic and geochemical evidence indicates that late-stage hydrothermal alteration played a crucial role in uranium remobilization and ore enrichment. Sulphide minerals, including cobaltite (CoAsS), galena (PbS), arsenopyrite (FeAsS), and chalcopyrite (CuFeS₂), are intimately associated with uranium phases and likely acted as effective reductants and sorption substrates, facilitating uranium precipitation under reducing conditions. The ore assemblage is accompanied by abundant accessory minerals such as zircon, allanite, and apatite. Substitution of U⁴⁺ for Zr⁴⁺ in zircon locally records uranium-rich hydrothermal fluids and contributes to zirconium enrichment. Collectively, these observations suggest that hydrothermal fluid–rock interaction and redox-controlled precipitation were the dominant processes responsible for uranium enrichment at the Bodal mine.

Keywords: Uranium mineralization; Hydrothermal alteration; Redox-controlled precipitation; Bodal mine; Central India

How to cite: Ganveer, S., Mallick, S. P., and Pruseth, K. L.: Hydrothermal remobilization and redox trapping of uranium in metabasalts of the Bodal mine, Central India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11094, https://doi.org/10.5194/egusphere-egu26-11094, 2026.

The Kirazlı porphyry and high-sulfidation (HS) epithermal system is situated in the central Biga Peninsula of northwestern Türkiye, a region characterized by the protracted closure of the Tethyan oceanic branches and the subsequent collision of Gondwana-derived continental fragments with the Sakarya Zone. This geodynamic framework facilitated the development of diverse tectono-magmatic environments, leading to the formation of porphyry and associated hydrothermal mineralization during the Cenozoic. Based on established geochronological data, magmatism in the Biga Peninsula occurred in five discrete chronostratigraphic episodes: Paleocene to Early Eocene (65–49 Ma), Middle–Late Eocene (49–35 Ma), Late Eocene to Early Oligocene (35–23 Ma), Late Oligocene to Middle Miocene (~23–14 Ma), and Late Miocene to Pliocene (14–5 Ma). Mineralization within the Kirazlı district is temporally constrained to two primary intervals—Late Eocene to Early Oligocene and Oligocene to Early Miocene corresponding to specific magmatic pulses and structurally mediated by major regional shear zones.

Integration of the ages of fault-hosting lithologies, structural styles, fault geometries, and paleostress reconstructions indicates three distinct tectonic phases consistent with the regional Cenozoic evolution: (1) NW–SE extension (Phase-1), (2) NNE–SSW extension (Phase-2), and (3) NE–SW extension (Phase-3). Detailed field observations, petrographic analysis, and microstructural investigations of oriented samples demonstrate that the porphyry and HS-epithermal stages were governed by these shifting stress regimes. B- and D-veins associated with the porphyry stage exhibit preferred orientations along an ENE–WSW strike, consistent with the NW–SE extensional regime of Phase-1. In contrast, late-stage quartz veins within the HS-epithermal overprint formed under a NNE–SSW extensional stress field, aligning with the Phase-2 tectonic pulse.

Analysis of fault planes for both Phase-2 and Phase-3 indicates that ENE–WSW and NE–SW strike directions are common to both phases. Phase-3 displays kinematic and geometric features characteristic of the modern transtensional NE–SW and strike-slip regime currently active in the Biga Peninsula. Correlation of these structural data with magmatism–mineralization age constraints indicates that the porphyry and HS-epithermal components of the Kirazlı system were emplaced during distinct tectonic periods. This evolution reflects the transition from a post-collisional setting to the current extensional and strike-slip dominated regime of western Anatolia.

How to cite: Çam, M., Kuşcu, İ., and Kaymakcı, N.: Tectono-Magmatic Evolution and Structural Controls on the Kirazlı Porphyry-High Sulfidation Epithermal System, Biga Peninsula, NW Türkiye, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11195, https://doi.org/10.5194/egusphere-egu26-11195, 2026.

El Chichón is an active volcano in Chiapas, Mexico, that features a hydrothermal system characterized by thermal springs, fumaroles and an acid crater lake. Many studies have focused on tracking the geochemical evolution of its fluids since its last eruption in 1982 and some have specifically aimed to evaluate the geothermal potential.  This work assesses the evolution of the geothermal potential through time using published geochemical data (1983-2025). We use geochemical diagrams, temperatures estimated with geothermometers and water-rock interaction analysis to identify the main system changes that influence the geothermal potential estimations. Given that El Chichón has been considered  a geothermal prospect since the 1980s, we discuss the possible uses of this resource in terms of its recent active seismicity, the risk scenarios and the local socio-cultural context. 

How to cite: Salas Ferman, J. L., Jácome Paz, M. P., Campion, R., Armienta, M. A., and Inguaggiato, S.:  Temporal evaluation of El Chichon´s geothermal potential in the period of 1983-2025. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15407, https://doi.org/10.5194/egusphere-egu26-15407, 2026.

Traditional methods for determining geopotential and height require successive transfers of leveling and gravity measurements, which are prone to error accumulation, face challenges in transoceanic applications, and are generally time-consuming, labor-intensive, and inefficient. Based on the principles of general relativity, an alternative approach using high-precision time-frequency signals to determine geopotential can overcome these limitations. In this study, simulation experiments were conducted to determine geopotential differences using BDS and Galileo five-frequency undifferenced carrier phase time-frequency transfer technology. The simulations employed clocks with different performance characteristics, utilizing precise clock offsets and multi-frequency observation data from both systems. The results show that the frequency stability achieved by BDS and Galileo five-frequency undifferenced carrier phase time-frequency transfer can reach approximately 3×10⁻¹⁷. The root mean square of the determined geopotential differences corresponds to centimeter-level equivalent height accuracy, and the convergence accuracy of the geopotential difference by the final epoch can reach better than 3.0 m²·s⁻². Given the rapid development of GNSS multi-frequency signals and ongoing improvements in the precision of products such as code and phase biases, geopotential determination based on Galileo and BDS multi-frequency signals is expected to have broader application prospects in the future. This study was supported by the National Natural Science Foundation of China project (No. 42304095), the Key Project of Natural Science Research in Universities of Anhui Province (No. 2023AH051634), the Chuzhou University Research Initiation Fund Project (No. 2023qd07).

How to cite: Xu, W. and Song, J.: Geopotential Difference Determination via BDS and Galileo Multi-Frequency Time-Frequency Signals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15725, https://doi.org/10.5194/egusphere-egu26-15725, 2026.

How well mixed is Earth's mantle? Are there primordial reservoirs? What fraction of the mantle feeds surface volcanism? We attempt to address these questions using large-scale Lagrangian particle tracking in time-reversed and forward convection models. We track particles backward in time using a Back-and-Forth Nudging (BFN) method applied to time-reversed thermal convection, initialized with a present-day seismic–geodynamic–mineral physics model (Glisovic & Forte, 2016, 2025). We likewise carried out long-term (multi-hundred-million-year) forward-in-time mantle convection simulations initialized with present-day mantle structure inferred from tomography. In all cases, we employ mantle viscosity structure that has been independently constrained and verified against a wide suite of present-day geodynamic observables that include free-air gravity anomalies, dynamic surface topography, horizontal divergence of plate velocities, excess core-mantle boundary ellipticity, and glacial isostatic adjustment data. A voxel-based analysis quantifies sampling density, residence time, and flux throughout the mantle.

We use different particle starting conditions, each designed to address a specific aspect of mantle mixing. To identify long-lived isolated regions, we track uniformly distributed particles both forward and backward in time, calculating residence times to locate candidate reservoirs. To estimate the sampling of lower mantle material in the upper mantle, we initialize particles in the D" layer and track them forward to determine what fraction reaches the upper mantle. To address plume dynamics and sampling, we place cylindrical arrays of particles beneath present-day hotspots and track them backward, using the statistical evolution of their standard deviation to quantify mixing along transport pathways, with transit time, and voxel analysis. To measure upper-to-lower mantle exchange, we initialize particles uniformly in the upper mantle. By combining these approaches, we systematically identify regions of low flux and high residence time, candidates for reservoirs. We further take a statistical approach based on voxel density sampling to quantify mixing across the volume of the mantle.

How to cite: Johnston, G., Anderson, M., Forte, A., and Glišović, P.: How Well Is the Mantle Sampled? A Global Voxel-Based Analysis of Residence Time and Flux from Forward- and Reverse-Time Mantle Convection, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15990, https://doi.org/10.5194/egusphere-egu26-15990, 2026.

Accurate geoid models are essential for converting GNSS-derived heights into physically meaningful elevations and for ensuring consistency in modern height reference systems. This study presents a unified geodetic framework for refining gravimetric geoids using GNSS/leveling residuals through physically interpretable fitting models. Five correction representations are evaluated, ranging from local Cartesian planar surfaces to geodetically consistent spherical formulations of increasing degree. The analysis demonstrates that low-order models effectively remove regional bias and tilt but show limited predictive stability. To enhance robustness, iteratively reweighted least squares is applied to mitigate the influence of outliers while preserving deterministic structure. Higher-order geodetic models are stabilized using ridge regularization, with the regularization strength selected objectively through leave-one-out cross-validation. This strategy ensures numerical conditioning while directly optimizing predictive performance. Results show that the full degree-2 geodetic model offers the best balance among accuracy, stability, and physical interpretability. It reduces long-wavelength distortions while maintaining consistent in-sample and cross-validated performance. The proposed approach supports reliable GNSS-based height determination in modern vertical datum realization and height modernization efforts.

How to cite: Abdalla, A. and Dwira, C.: Geodetic degree-based Models for Robust Regional Geoid Refinement, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16148, https://doi.org/10.5194/egusphere-egu26-16148, 2026.

Sulfur released by magmatic activity strongly impacts the climate and is essential for ore mineralisation. Many porphyry systems contain up to billions of tons of sulfur, far exceeding the sulfur capacity of silicate melt and therefore requiring an additional, efficient S‑transfer mechanism.

We present a unique mafic rock (SiO₂ = 53–59 wt.%, MgO = 5.3–7.3 wt.%) containing ~15–20 vol.% anhydrite, ~30–40 vol.% biotite and ~40–50 vol.% plagioclase from the largest porphyry–epithermal system in China. Magmatic anhydrite, indicated by textural relations and LREE‑rich compositions, yields bulk‑rock S contents of ~2–3 wt.%, far above experimental S solubilities.

Plagioclase shows sharp core–rim decreases from An₅₀–₇₀ to An₂₅–₄₅, recording strong CaO depletion caused by sulfate saturation. Extensive sulfate saturation also suppressed amphibole/orthopyroxene and removed a large proportion of LREEs from the melt, producing flat REE patterns in co-crystallised apatite. Biotite exhibits pronounced Ba depletion from core to rim. Because Ba partitions strongly into sulfate melt, not into anhydrite, this Ba zoning is best explained by the formation of a sulfate melt, rather than by crystallisation of anhydrite from a silicate melt.

Nd isotopic compositions (ԑNd(t) ≈ -1.0) indicate that the magma was derived from partial melting of the mantle wedge. We suggest that ascent of this oxidised, sulfur‑rich mafic magma led to decompression-driven oxidation of S²⁻ to S⁶⁺, sulfate saturation, and exsolution of an immiscible sulfate melt. This discrete sulfate‑melt migrated upward and provided an efficient pathway for long‑distance transfer of large amounts of sulfur to porphyry systems. This sulfate‑melt exsolution process is a previously unrecognised mechanism that relaxes the constraint imposed by the sulfur capacity of silicate melt, and LREE‑depleted apatite associated with abundant magmatic sulfate phases may serve as an indicator of sulfate‑melt exsolution and a proxy for porphyry mineralisation potential in the upper crust.

How to cite: Huang, W., Humphreys, M., and Liang, H.: Magmatic sulfate‑melt exsolution as a mechanism for excess sulfur in porphyry systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22040, https://doi.org/10.5194/egusphere-egu26-22040, 2026.

Gravity data, comprising a key foundational dataset, are crucial for various research, including land subsidence monitoring, geological exploration, and navigational positioning. However, the collection of gravity data in specific regions is difficult because of environmental, technical, and economic constraints, resulting in a non-uniform distribution of the observational data. Traditionally, interpolation methods such as Kriging have been widely used to deal with data gaps; however, their predictive accuracy in regions with sparse data still needs improvement. In recent years, the rapid development of artificial intelligence has opened up a new opportunity for data prediction. In this study, utilizing the EGM2008 satellite gravity model, we conducted a comprehensive analysis of three machine learning algorithms—random forest, support vector machine, and recurrent neural network—and compared their performances against the traditional Kriging interpolation method. The results indicate that machine learning methods exhibit a marked advantage in gravity data prediction, significantly enhancing the predictive accuracy.

How to cite: Zhang, Y., Liu, Y., Wu, Y., and Pang, Q.: Gravity Predictions in Data-Missing Areas Using Machine Learning Methods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2392, https://doi.org/10.5194/egusphere-egu26-2392, 2026.

Tropospheric wet delay remains a key error source for space geodesy, including GNSS, VLBI, and InSAR. Empirical models such as GPT3 are widely used, yet they rely on simplified parameterizations and fixed coefficient tables that limit modeling capacity. Frequent updates are difficult because the entire archive must be reprocessed. With the rapid progress of machine learning, it is natural to seek ML-based tropospheric models that improve both accuracy and efficiency. To date, most work has focused on zenith wet delay (ZWD), which is essentially one-dimensional, while fully data-driven slant modeling has been largely unexplored. Slant wet delays (SWD) are inherently anisotropic, which makes the task more challenging.

We propose a hybrid ML framework that embeds a physical layer inside the network to predict SWD end-to-end and yields consistent ZWD and wet mapping function as internal outputs. Training uses hundreds of millions of ERA5 ray-traced samples from 2018 to 2022 with global coverage. The resulting ML model outperforms GPT3 for SWD, with markedly lower errors over continental regions where most space-geodetic stations operate and with the largest gains at low elevation angles and along coasts. The learned mapping is asymmetric in elevation and azimuth, which removes the need for explicit horizontal gradients. As ancillary products, the framework provides ZWD that surpasses GPT3 and a wet mapping function that exceeds the symmetric GPT3 variant and is comparable to the asymmetric one. We also develop augmented variants that accept surface temperature and water vapor pressure as inputs and obtain further accuracy gains. To our knowledge, this is the first ML-based model that directly predicts SWD. The model is compact and faster than GPT3 when applied to large sample sets. The hybrid design supports efficient fine-tuning with new observations and provides a practical path to maintainable routine processing and continued advances in space-geodetic troposphere modeling.

How to cite: Zhang, Z. and Soja, B.: Hybrid Machine-Learning Framework for Slant Wet Delay Modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2814, https://doi.org/10.5194/egusphere-egu26-2814, 2026.

The ionosphere introduces dispersive delays on GNSS signals, with the magnitude of the error determined by the slant total electron content (STEC) along the satellite–receiver path. Standard correction products, such as Global Ionospheric Maps (GIMs), estimate vertical TEC (VTEC) on coarse spatio-temporal grids, relying on thin-shell assumptions and mapping functions to convert between STEC and VTEC. While effective for many applications, these simplifications limit accuracy, particularly during disturbed ionospheric conditions.

In this work, we present a machine learning–based model for direct STEC prediction, avoiding the need for VTEC mapping. The model is implemented as a ResNet-like multi-layer perceptron (MLP) trained with Gaussian negative log likelihood loss, which allows us to provide uncertainties along with the STEC. To ensure global applicability, the dataset spans observations of the IGS network from 2014 until 2025 and thus more than a full solar cycle, covering diurnal, seasonal, and solar variability. Input features include spatial geometry (station and satellite coordinates, azimuth, elevation), temporal information (time of day, day of year), and space weather indices, enabling the network to capture both spatio-temporal dependencies and heliophysical drivers of ionospheric variability.

The pretrained model shows strong agreement with observed STEC (r = 0.95, R² = 0.90) and generalizes robustly across years without daily fitting. Errors scale with STEC magnitude but remain unbiased, reflecting physically consistent behavior under varying ionospheric conditions. On temporally held-out data, the mean absolute error is ~7.2 TECU, with improved performance for interpolation (~4.6 TECU) compared to extrapolation (~9.2 TECU). Daily fine-tuning additionally improves performance, particularly at low elevation angles where VTEC-based mapping functions are weakest, while maintaining comparable accuracy at high elevations. Performance on unseen stations is competitive with established VTEC-based models and global ionospheric maps.

By directly modelling STEC from raw GNSS observations across a solar cycle, this approach provides a flexible, observation-driven alternative to mapping function based models, with applications in precise GNSS positioning, space weather monitoring, and multi-technique ionospheric research.

How to cite: Rüegg, A., Mao, S., and Soja, B.: Ionospheric Slant TEC Modelling Based on GNSS Data with Machine Learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3285, https://doi.org/10.5194/egusphere-egu26-3285, 2026.

Tropospheric delay is primary limitation for surface deformation retrieval using Synthetic Aperture Radar Interferometry (InSAR), presents challenges due to its spatiotemporal heterogeneity. This study proposes a correction framework integrating geodetic parameter estimation theory with deep learning. It aims to robustly estimate topography-correlated stratified delays while also rigorously applying a new deep learning network to suppress turbulent delays. Initially, a quadtree segmentation method is employed to partition the area of interest. Within each homogeneous segment, the topography-correlated stratified delay phase is robustly estimated using an adaptive-order functional model fitted via weighted least squares. Subsequently, the time-domain differentiation technique is applied to isolate high-frequency turbulent signals, thereby constructing a realistic turbulent sample dataset. Finally, by integrating the strengths of the U-Net architecture and the Convolutional Block Attention Module (CBAM), a Spatio-Temporal Turbulence U-Net (STTU-Net) is designed based on the statistical spatio-temporal characteristics of the real turbulence sample dataset. This network learns the detailed evolution of random turbulent fields, enabling an efficient, data-driven deep learning approach for turbulent delay correction. Applied to Sentinel-1 data over Southern California, the method reduces the average interferogram phase standard deviation by 27% and weakens phase-elevation correlation. After full correction, the RMSE between InSAR and GNSS time series decreases from 4.7 cm to 2.2 cm. The estimated total delays also agree well with GNSS-ZTD (correlation: 0.84; RMSD: 1.94 cm). Results from simulated data confirm that this method effectively suppresses tropospheric delay while fully preserving genuine deformation signals of varying characteristics, thereby providing a systematic and verifiable solution for tropospheric delay correction in InSAR.

How to cite: Si, J., Zhang, S., Zhao, J., and Lu, Z.: Geodesy-Informed Deep Learning for InSAR Tropospheric Correction: Adaptive Weighted least squares and STTU-Net, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3777, https://doi.org/10.5194/egusphere-egu26-3777, 2026.

The proposed approach aims to deliver near-real-time or short-term seeing estimates to support operational decision-making, improve scheduling efficiency, and enhance data quality for astronomical observations and emerging geodetic infrastructure, including the planned Lunar Laser Ranging facility in South Africa. By leveraging existing, lower-cost instrumentation, this framework offers a scalable and transferable solution for site characterization and operational support at current and future geodetic observatories.

Keywords: Astronomical seeing, Geodesy, Laser Ranging (SLR/LLR), Atmospheric turbulence, Site characterization

How to cite: Nyide, S.: Machine Learning Based Prediction of Astronomical Seeing Using All-Sky Camera Images and Cloud Sensor Data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6625, https://doi.org/10.5194/egusphere-egu26-6625, 2026.

Monitoring the deformation behavior of embankment dams is essential to ensure their structural integrity and long-term performance. Conventional geodetic methods, such as precision leveling, offer high spatial accuracy but limited temporal coverage, while in-situ geotechnical sensors, such as settlement meters, provide continuous but localized measurements. This study proposes an improved method of geodetic/geometrical deformation analysis based on strain theory, by merging displacement data from leveling and settlement meters to estimate settlements at the dam surface. This approach, based on MMC principles, allows for an appropriate visualization and interpretation of the settlement occurring and can be used for the detection of abnormal settlement behavior. Applied to a real case of an Algerian rockfill dam, the proposed method shows, after some validation and comparison with subsequent research results, a good adequacy in identifying settlement behavior. The results highlight the reliability and robustness of the geodetic model improved by multi-sensor data fusion in estimating deformations in critical geotechnical infrastructures.

Key words. Geodetic model, Strain analysis, Multi-sensor data fusion, dam settlement, levelling, settlement meter.

How to cite: Attaouia, B., Chouicha, K., and Salem, K.: Advanced Geodetic Deformation Analysis Based on Multi-Sensor Data Fusion., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6644, https://doi.org/10.5194/egusphere-egu26-6644, 2026.

Precise monitoring of Earth's crustal deformation relies heavily on the analysis of Global Positioning System (GPS) displacement time series recorded by the set of ground-based antennas. This monitoring is possible for the period during which the GPS station is operational. In this presentation, we undertake one of the first attempts to forecast daily GPS displacements for 13 randomly selected stations in Europe, for which the displacements were recorded from 1996 to 2023. We use vertical displacements provided by the Nevada Geodetic Laboratory (NGL) and pre-process them thoroughly. We then apply the Long Short-Term Memory (LSTM) network, one of the Deep Learning approaches, and evaluate its efficiency for long-term forecasting of GPS displacements over two-year horizon. The performance of the data-driven LSTM network is compared against the standard statistical AutoRegressive Integrated Moving Average (ARIMA) prediction method. We also quantify the impact of data pre-processing strategies on forecast accuracy, specifically gap-filling techniques, such as linear interpolation, Piecewise Cubic Hermite Interpolating Polynomial (PCHIP), a seasonality-based Least Squares (LS) reconstruction, and raw data processing without interpolation are assessed. The models were evaluated using Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), and the coefficient of determination (R²). Statistical significance was assessed using the Friedman test followed by the Nemenyi post-hoc test. Results indicate that the LSTM network significantly outperforms the ARIMA model in long-term forecasting. The hybrid approach combining LSTM with LS-based interpolation yielded the highest accuracy. Furthermore, degradation analysis reveals that the LSTM model maintains stability and lower error accumulation over the forecast horizon. These findings indicate that LSTM networks, particularly when combined with seasonality-aware interpolation (LS), offer a significant improvement in forecasting accuracy and stability compared to the standard ARIMA model. The results underscore the substantial potential of deep learning methodologies in geodetic time series analysis, encouraging their further exploration as robust alternatives to statistic approaches.

How to cite: Rados, J. and Klos, A.: Forecasting GPS displacements with a Long Short-Term Memory (LSTM) network, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6725, https://doi.org/10.5194/egusphere-egu26-6725, 2026.

Regional sea level change is driven by multiple physical processes, resulting in complex dynamics and pronounced spatio–temporal heterogeneity. This study proposes a hybrid framework that integrates the physical fingerprints with deep learning to achieve both sea level budget closure and temporal prediction of regional sea level variations. Total sea level changes are firstly decomposed into the steric and barystatic components. By further considering the mass redistribution of ice sheets, glaciers, and terrestrial water storage and their associated sea level fingerprints, the cryo–hydrological contribution (CHC) sea level, is introduced to replace the traditional barystatic term. This substitutes direct observations of local mass change with the sea level response to mass redistributions occurring elsewhere, thereby enhancing the physical interpretability of the decomposition. Subsequently, a convolutional neural network and bidirectional long short-term memory hybrid model is employed to jointly predict the total, steric, barystatic, and CHC sea level components.

We quantify the impacts of mass variations in cryo–hydrological domain on sea level changes across 20 oceanic regions, achieving a quantitative projection from mass redistribution to sea level response. Results demonstrate excellent budget closure within the analyzed regions, with mean correlation coefficients exceeding 0.9 and root mean square difference of approximately 15 mm. In the temporal domain, the deep learning network effectively reproduces both long-term trends and seasonal oscillations (correlation ≥ 0.8 in most prediction windows). From a physical perspective, the presented study establishes the regional sea level response to cryo–hydrological mass redistribution and demonstrates strong practical relevance.

How to cite: qiu, F., Gruber, T., and Pail, R.: Linking Cryo–Hydrological Mass Redistribution to Regional Sea Level Change through Hybrid Physics–AI Modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6833, https://doi.org/10.5194/egusphere-egu26-6833, 2026.

Precise Point Positioning (PPP) provides high accuracy positioning using a single GNSS receiver, but its performance is often limited by station-specific multipath errors. This study presents a novel Principal Component Analysis (PCA) and machine learning based Multipath Hemispherical Map (PM-MHM) approach to mitigate multipath effects in PPP mode. Network-wide correlated errors (NWCEs), including satellite orbit and clock errors as well as unmodeled tropospheric wet delays, are first isolated and removed using PCA, allowing the remaining station-specific residuals to be interpreted as multipath. The PM-MHM employs a hybrid machine learning framework that integrates a global model with localized, grid-specific correction models to adaptively capture multipath patterns. In this study, we develop an automatic fitting training scheme that evaluates multiple algorithms, including Random Forest, Least Squares Boosting and Extreme Gradient Boosting. The model is trained on six consecutive days of PPP residuals and evaluated on independent datasets, demonstrating superior performance compared with the Trend Surface Analysis-based MHM (T-MHM). For pseudorange and carrier phase observations, PM-MHM achieves mean RMSE reductions of 39.8% and 37.3%, respectively, outperforming T-MHM by 10-15%. Furthermore, PCA decomposition of Up-component residuals reveals that the low frequency portion of the first principal component (PC1_low) effectively captures tropospheric zenith wet delay (ZWD) variations. Incorporation of PC1_low into GNSS-derived ZWD improves correlation with radiometer measurements by about 0.08 and reduces RMSE by 6.32%. These results demonstrate that PM-MHM not only offers high accuracy multipath mitigation but also enables the physical analysis of other residual components beyond multipath, highlighting its potential for improved PPP-based atmospheric monitoring and high precision positioning applications. 

How to cite: Wang, L. and Kuttere, H.: Observation-Level PCA and Machine Learning for Multipath Mitigation in GNSS PPP with Tropospheric Wet Delay Assessment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9475, https://doi.org/10.5194/egusphere-egu26-9475, 2026.

High-resolution laser strainmeter measurements in an underground gallery at Moxa Geodynamic Observatory (Thuringia, central Germany) provide detailed records of crustal deformation. Beyond Earth tides, deformation induced by pore-pressure fluctuations produces the largest signals. These observations reveal that the relationship between groundwater transport and crustal strain is temporally fluctuating, highlighting the need for a quantitative approach to systematically characterize potential coupling.

Here, we present a physics-guided, data-driven approach for estimating effective groundwater–strain coupling from multivariate time series of groundwater levels and nanometer-scale strain measurements, based on linear Biot poro-elasticity. The approach incorporates physically guided Biot neurons into an autoregressive neural network architecture; these neurons model horizontal poro-elastic responses of fractured rock driven by groundwater variations. It dynamically adjusts to temporal changes in groundwater levels and the resulting pore-pressure-induced strain. Using orientation-specific laser strainmeter measurements and spatially distributed groundwater levels from boreholes, we estimate Biot coupling in two horizontal directions (North–South and East–West) and derive effective coupling parameters from over a decade of observatory records.

Our results provide insights into the dynamic hydro-mechanical behaviour of the shallow crust and highlight the potential of physics-guided neural architectures to support the interpretation of high-resolution deformation and stress–strain responses in geomechanical studies.

How to cite: Kasburg, V. and Kukowski, N.: Physics-Guided Neural Network Parameter Estimation of Groundwater–Strain Coupling at Moxa Geodynamic Observatory, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11511, https://doi.org/10.5194/egusphere-egu26-11511, 2026.

Interferogram denoising is a critical step in interferometric synthetic aperture radar (InSAR) data processing, as it directly affects the accuracy and reliability of final products, such as surface deformation measurements and digital elevation models. Current state-of-the-art data-driven denoising models primarily rely on training datasets with noise simulated using statistical models, such as the complex Gaussian distribution. While effective in controlled scenarios, these simulated noises often fail to capture the intricate variability of real-world interferometric noise, leading to degraded performance in practical applications. In this study, we propose a semi-supervised self-boosting learning method for InSAR phase denoising, marking the first instance of training a model using real-world noise. The method consists of two phases: (1) Model excitation, where the model is initially trained with simulated noise to develop basic denoising capabilities; (2) Refinement boosting, an unsupervised, iterative process where the model gradually refines itself using real-world noise. Specifically, this phase involves four interconnected steps: noise extraction, where noise is extracted from real interferograms; noise purification, which removes residual signal components; data augmentation, where purified noise is updated into the training dataset; and model enhancement, which iteratively refines the model to improve its generalization to real interferograms. We identified the cost-optimal denoising model by conducting experiments across network architectures of varying complexity, using identical training datasets and experimental settings. Experimental results validate the effectiveness of the proposed method on both synthetic interferograms with varying coherence levels and real Sentinel-1 interferograms. On synthetic data, the method demonstrates superior denoising performance, achieving the lowest root mean square errors (RMSE) and highest structural similarity index measures (SSIM) compared to state-of-the-art techniques such as NL-InSAR and InSAR-BM3D, while maintaining comparable inference speeds to simpler methods like BoxCar. On Sentinel-1 interferograms, the approach consistently delivers improved denoising results, as evidenced by fewest phase residues and smoothest phase unwrapping. Our findings also reveal that when training data is comprehensive and well-aligned, increasing model complexity does not necessarily lead to giant improvement; simpler architectures can yield results comparable to those of more sophisticated models. Additionally, by analyzing noises simulated from the coherence-guided statistical model and those extracted from Sentinel-1 interferograms, we observe a significant discrepancy between simulated and real noise distributions, with the former failing to capture the complexities of real-world noise. This underscores the importance of incorporating real-world noise into training datasets for InSAR data-driven models, e.g., denoising, unwrapping, and other applications. Overall, this research introduces a robust methodology for interferogram denoising and enhances our understanding of the complexities of real-world interferometric noise, paving the way for further advancements in noise modeling and interferogram restoration.

How to cite: Zhang, Q. and Wang, T.: A Semi-Supervised Self-Boosting Learning Method for InSAR Phase Denoising, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11670, https://doi.org/10.5194/egusphere-egu26-11670, 2026.

Terrestrial Water Storage Anomalies (TWSA) derived from satellite gravimetry provide a unique, integrated measure of large-scale hydrological conditions and have been widely used to characterize flood-prone states at basin scale. However, their applicability for flood monitoring and early warning is constrained by the coarse spatial resolution of current gravimetric products (approximately 300 km), which limits the detection of localized storage anomalies relevant for flood initiation and timing.

An unsupervised deep-learning approach based on convolutional neural networks is used to downscale TWS grids from Next-Generation Gravity Mission (NGGM) and ESA–NASA MAGIC constellation simulated products from 3° to 1° with a five daily frequency. With this new constellation, the NASA-DLR GRACE-C pair will ensure continuity and spatial coverage, while the ESA NGGM will provide increased sensitivity, novel products and pre-operational capabilities, contributing for over 90% to the MAGIC mission performance over the hydrologically relevant areas. The joint ESA-NASA MAGIC constellation will provide 5-daily gravity field products on a global scale with a spatial resolution of approximately 200 km, also reducing latency and uncertainties with respect to present gravimetry missions.

Simulated satellite products corresponding to the GRACE-C, NGGM and MAGIC mission scenarios are obtained from realistic end-to-end (E2E) closed-loop experiments carried out in the context of ESA studies, while the downscaling task is assigned to a U-Net module integrating ERA5-Land climate variables and the ETOPO2022 Digital Elevation Model. The ground truth solution of the gravity field is given by the ESA ESM 2.0, allowing for a-posteriori validation of the downscaling framework. The downscaled maps present high spatial and temporal correlation with the ground truth, reconstructing fine-scale TWS patterns without losing structural coherence at the native resolution of the satellite product. The pipeline is also extended to real GRACE/GRACE-FO data for real-world applications. The obtained results highlight the potential of unsupervised machine learning approaches for regional hydrological monitoring.

For this purpose, the derived downscaled products are used for the identification of critical hydrological states in the context of extreme event detection using classical threshold-based indicators derived from TWS climatological anomalies. The analysis discusses how improved spatial resolution may help preserve sharper anomaly structures that are otherwise smoothed at coarse scales, with possible benefits for the timely identification of critical states. The early-warning pipeline is evaluated in terms of event detection skill and timing based on the true critical states derived from the ground truth TWS in the closed-loop simulations and then extended to real GRACE data.

How to cite: Goracci, G. and Daras, I.: Towards hydrological extreme event monitoring using deep learning-downscaled NGGM and MAGIC data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12469, https://doi.org/10.5194/egusphere-egu26-12469, 2026.

Zenith Total Delay (ZTD) derived from Global Navigation Satellite System (GNSS) observations is a critical parameter for precise positioning and atmospheric studies. ZTD is continuously estimated at GNSS stations, forming high-resolution temporal time series that reflect the dynamic behavior of the troposphere. In recent years, deep learning approaches have been increasingly applied to ZTD estimation due to their ability to model nonlinear relationships. However, particularly for time-series reconstruction problems, it remains an open question whether the added architectural complexity of such models is always necessary.

In this study, feature-driven classical machine learning models and a data-driven neural network approach are systematically compared for reconstructing missing ZTD values in GNSS time series. The analysis is based on ZTD observations from six International GNSS Service (IGS) stations covering the period from February 2023 to January 2024. All models are trained using an identical feature set comprising lagged ZTD values, tropospheric gradients, ZTD variances, station coordinates, and temporal attributes. This design ensures a fair and interpretable comparison between different modeling approaches.

Linear Regression is considered as a baseline model, while Random Forest represents a nonlinear yet interpretable machine learning approach, and a Fully Connected Neural Network (FNN) is employed as a deep learning model. Model performance is evaluated using Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and the coefficient of determination (R²), with a leave-one-station-out validation strategy applied to assess generalization capability.

The results indicate that the Random Forest model achieves accuracy comparable to that of the FNN, while exhibiting greater stability and consistency across stations. The results highlight that incorporating physically meaningful features into the input space can be as effective as increasing model complexity for ZTD reconstruction. The study provides methodological and practical insights for selecting appropriate modeling strategies in tropospheric delay estimation.

How to cite: Tekin Ünlütürk, N. and Bak, M.: Comparing Feature-Driven and Data-Driven Models for GNSS-Based ZTD Reconstruction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14292, https://doi.org/10.5194/egusphere-egu26-14292, 2026.

Hydrological and hydro-geodetic applications increasingly require high-resolution characterization of aquifer-scale water-storage dynamics over large regions, while existing hydrology models and gravimetric observations operate at much coarser spatial resolution. InSAR provides dense surface-deformation observations sensitive to subsurface water-storage changes, but converting these measurements into reliable, vertically resolved hydrological information remains an ill-posed and computationally demanding inversion problem, especially for multi-decadal, multi-mission data sets.

We present a physics-aware machine-learning framework to enable large-scale, high-resolution hydro-geodetic inversion from long-term InSAR time series. Independent InSAR deformation time series from open SAR missions (ERS-1/2, Envisat, ALOS-1/2, Sentinel-1) are processed using reproducible workflows and harmonized across wavelengths and acquisition geometries to form spatio-temporal deformation volumes. These data are inverted using a 3D Swin Transformer U-Net constrained by elastic and poroelastic forward deformation operators and basin-scale mass conservation. Hydrological models and gravimetric observations are used as structured supervision rather than ground truth, ensuring physical consistency and stability of the inversion.

The live demonstration emphasizes scalable execution on high-performance computing platforms, reliable inversion of massive InSAR data batches, and interpretable aquifer-scale hydrological responses, including characteristic lag behaviour. The framework supports high-resolution hydrological model improvement and provides physically consistent inputs for groundwater-related geohazard assessment, such as subsidence and compaction risk.

Key words: Physics-aware machine learning; 3D Swin Transformer U-Net; InSAR time-series inversion; hydro-geodetic analysis; high-performance computing (HPC)

How to cite: Shafiei Joud, M., Yang, F., and Chawla, S.: Physics-Aware Machine Learning for Large-Scale Hydro-Geodetic Inference from InSAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14591, https://doi.org/10.5194/egusphere-egu26-14591, 2026.

Accurately representing atmospheric humidity is critical for Artificial Intelligence (AI)-based weather forecasting models, which mostly rely on physics-based weather data such as ERA5 in both training and deployment stages. Unlike physics-based weather forecasting models, which continuously use humidity observations from different sources through data assimilation techniques, AI weather models are not equipped with a data assimilation framework to integrate observations into their system. This is one of the most important limitations of these models, which limits their ability to forecast small-scale weather events that are mainly due to convection processes and are related to humidity. To address this gap, there is a need to develop an AI-based data assimilation framework for integrating reliable observations into current AI-based weather forecasting models as an auxiliary component.

Global Navigation Satellite Systems (GNSS) observations provide reliable humidity measurements with strong sensitivity to the wet refractivity of the atmosphere, which plays an important role in numerical weather prediction, GNSS positioning, and atmospheric monitoring.

In this study, as an initial step, we present a physics-informed deep learning-based framework to assimilate ground-based and space-based GNSS data into ERA5 Three-Dimensional (3D) wet refractivity fields.

The proposed framework assimilates ground-based GNSS Zenith Wet Delays (ZWD), GNSS Radio Occultation (RO) profiles, radiosonde measurements, and voxel mask data that represent the number of signal rays intersecting each voxel, as derived from a ray-tracing technique, to update an initial 3D wet refractivity field from ERA5 data. A 3D Convolutional Neural Network (3D-CNN), which uses residual and convolutional block attention modules, is employed to capture the nonlinear relationships between multi-source observations and 3D wet refractivity distributions. The assimilation procedure is formulated using a hybrid physics-informed loss function that simultaneously constrains (i) GNSS ZWD consistency at station locations, (ii) voxel-wise agreement with RO-derived wet refractivity, (iii) adherence to the ERA5-based initial state, and (iv) bias reduction in ZWD. The updated 3D wet refractivity field is evaluated using ZWD derived from independent GNSS observations and radiosonde measurements.

The obtained results demonstrate that the proposed deep learning-based assimilation framework significantly improves 3D wet refractivity estimation and ZWD accuracy relative to the initial ERA5-driven state, while producing physically consistent structures. The framework provides a scalable pathway for assimilating humidity data from different types of GNSS measurements and other remote sensing techniques into reanalysis datasets, thereby enhancing the meteorological parameters used in AI-based weather forecasting models.

How to cite: Haji-Aghajany, S. and Rohm, W.: AI-Based GNSS Data Assimilation of ERA5 3D Wet Refractivity Fields: Initial Results, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16707, https://doi.org/10.5194/egusphere-egu26-16707, 2026.

Recent studies of the Reykjanes Peninsula in Iceland have shown that Interferometric Synthetic Aperture Radar (InSAR) data can reveal surface movements across new and pre-existing fractures associated with stress changes during volcanic dyke intrusions. These data have revealed many fractures in areas where optical imagery or field observations are obscured by vegetation, infrastructure, or young lava flows. Mapping active faults and fractures in geologically dynamic regions is essential for assessing tectonic and volcanic hazards, as pre-existing fractures and crustal weaknesses can control magma pathways, dyke propagation, and the location of eruptive activity. However, systematic fracture mapping from wrapped interferograms remains a time-consuming manual task. Deep learning approaches have been widely utilized successfully for mapping faults in seismic data and optical images, and similarly, to detect glacier crevasses in SAR backscatter images. Here, we investigate the feasibility of automatic fracture mapping directly from wrapped interferograms using deep learning, focusing on the current volcanic unrest on the Reykjanes Peninsula. We address the task as a binary classification problem, and implement a convolutional neural network with a U-Net architecture trained using a Dice loss to address strong class imbalance. We initially trained our model on a rather small, highly imbalanced dataset consisting of Sentinel-1 and TerraSAR-X interferograms of the area from September 2023 to February 2024. Despite relatively modest F1-Score (~56%), the model successfully identifies all major fracture movements in the test data and is able to detect features absent from the original labels, providing a fairly robust fracture map that can be easily refined. These results demonstrate that deep learning can be used to extract meaningful structural information from wrapped interferograms, even with limited data and imperfect training labels, and constitute to the best our knowledge the first application of deep learning to fracture mapping in wrapped interferograms. Current work is aimed at improving the model performance by including the latest fractures dataset of the Reykjanes Peninsula, consisting of fractures mapped on TerraSAR-X interferograms from September 2021 to July 2024. Additionally, ongoing efforts are focused on generating physically realistic synthetic interferograms that capture the complexity of fracturing and fracture reactivation due to dyke emplacement and propagation and other sources of deformation. By addressing the current limitations, this approach has the potential to enable transferable fracture-mapping workflows applicable across diverse tectonic settings and InSAR datasets, contributing to more efficient geohazard monitoring.

How to cite: Barreto, A., Wire, N., Birgisdóttir, Á., Nobile, A., Geirsson, H., and Jónsson, S.: Fracture mapping in InSAR data using deep learning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18677, https://doi.org/10.5194/egusphere-egu26-18677, 2026.

With growing concerns about climate change, increasing natural hazards, and extreme weather events, monitoring Earth’s surface parameters has become a critical area of interest for both the scientific community and society. Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative and low-cost technique that exploits existing Global Navigation Satellite System (GNSS) signals after reflection from Earth’s surface. GNSS-R constellations offer unique observations with unprecedented data volume, temporal resolution, and spatial coverage across the entire globe under all-weather conditions. As the data volumes are continuously accumulating, the trend in applying Artificial Intelligence (AI) is expanding. However, current AI models rely heavily on labelled data, feature engineering, and extra fine-tuning, leading to high computational and labor costs. To address these issues, we propose the project EcoGEM: Energy-efficient Multimodal GNSS Reflectometry Models for Generalist Earth Surface Monitoring and Hazard Response.

EcoGEM develops cutting-edge Earth observation foundation models using GNSS-R measurements and integrates them with other remote sensing data. It pioneers the first general-purpose GNSS-R foundation models and curated multimodal datasets to support climate science, hazard detection, and environmental monitoring. Unlike task-specific methods, the proposed models adapt across applications such as soil moisture, vegetation water content, and ocean wind speed. Uniquely, EcoGEM emphasizes energy-efficient AI through model pruning, knowledge distillation, and dynamic architectures, enabling deployment on edge devices and small satellite platforms. This collaborative project of GFZ and DLR advances sustainable AI and promotes novel and open-access tools for Earth scientists, environmental policymakers, and global users.

How to cite: Asgarimehr, M., Zhao, D., Xiao, T., Izadgoshasb, H., Wickert, J., and Kuzu, R.: GNSS Reflectometry AI based Models for Matvariate Earth Surface Monitoring and Hazard Response  , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20001, https://doi.org/10.5194/egusphere-egu26-20001, 2026.

GNSS Meteorology is an increasingly important source of atmospheric observations, providing near-real-time information on tropospheric water vapor derived from GNSS signal delays. These observations become especially valuable when available at high density, enabling improved characterization of mesoscale moisture gradients and rapidly evolving atmospheric structures. Skyfora’s Telecom GNSS Meteorology enables such dense coverage by repurposing existing telecom infrastructure as a distributed atmospheric sensing network and extracting GNSS-derived delay information at scale. Such observation streams are particularly valuable in regions where conventional radiosonde, radar, or dense surface networks are limited.

In this contribution, we present an AI-enabled data assimilation method for integrating GNSS-derived tropospheric parameters into modern weather modelling systems. Rather than relying on classical variational methods alone (3D-Var, 4D-Var) and their associated linearized observation operators and background-error assumptions, the approach leverages generative, physics-informed machine learning models to produce dynamically consistent atmospheric state estimates while accounting for observational uncertainty and irregular sampling.

We further highlight the practical deployment of GNSS Meteorology through two demonstration case studies: (i) a national-scale network trial in Latvia and (ii) a live demonstration in the Barcelona region. Together, these cases illustrate how GNSS-derived atmospheric observations can be operationalized into scalable atmospheric monitoring capabilities. The results emphasize the potential of combining novel observation networks with AI-based assimilation to enhance atmospheric situational awareness and support future improvements in forecast skill.

How to cite: Matakos, A., Peralta, C., Renaldo, N., Santala, J., and Kaisti, K.: GNSS Meteorology: AI-Enabled Assimilation of GNSS-derived Tropospheric Parameters with Two Demonstrated Case Studies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21895, https://doi.org/10.5194/egusphere-egu26-21895, 2026.

Gravitational data from satellites in Earth’s orbit can be used to reconstruct secular and
periodic mass movements at the Earth’s surface. These include tidal effects caused by the
Moon, seasonal variations in rainfall, and the melting of glacial ice at the poles.
Such mass transports not only lead to variations in the observed gravitational signal, but
also act as surface loads that induce elastic deformation of the Earth on short timescales.
In this talk, we present a method for calculating these deformations using the finite element
method (FEM), along with some numerical examples. Finally, we outline directions for future
research, in particular the inverse problem of reconstructing surface mass distributions from
GRACE data while explicitly accounting for deformational effects.

How to cite: Peter, T.-J., Michel, V., and Suttmeier, F.-T.: Elastic deformation of the Earth due to surface loading: finite element modelling and implications for inverse gravimetry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1803, https://doi.org/10.5194/egusphere-egu26-1803, 2026.

Within the window remove-restore technique (Abd-Elmotaal and Kühtreiber, 2003), the effect of the topographic-isostatic masses is removed from the source free-air gravity anomalies using high-resolution Digital Terrain Models (DTMs) and a terrain correction software, e.g., TC-program (Forsberg, 1984). A harmonic analysis of the topographic-isostatic masses is then applied to compute the effect of the topographic-isostatic masses over the data window to adapt the used geopotential model, in order to avoid a double consideration of their contribution. In this study, it is intended to use only the topographic masses in the window remove-restore technique and to compare the results with the case of using the topographic-isostatic masses. This comparison allows estimating the effect of the isostatic masses in the framework of the window remove-restore technique. The quantification of the effect is done for two mountainous regions, the Alps in Austria and the Rocky Mountains region in Colorado. The comparison is performed at two levels: reduced anomalies and computed geoidal heights. The results demonstrate the impact of the isostatic masses in window remove-restore technique and are discussed in detail.

How to cite: Abd-Elmotaal, H. and Kühtreiber, N.: Effect of Isostatic Masses in the Framework of the Window Remove-Restore Technique, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3074, https://doi.org/10.5194/egusphere-egu26-3074, 2026.

This poster presents a numerical scheme based on the Discrete Duality Finite Volume (DDFV) method for solving boundary value problems with oblique derivative boundary conditions. Such problems arise in various engineering applications where the boundary behavior of the solution is prescribed in a non-normal direction. The formulation of the boundary value problem and the proposed scheme are described, and the main theoretical properties of the method are discussed. The performance of the method is then investigated using two theoretical two-dimensional numerical experiments. In the first experiment, the oblique derivative vector is generated solely by translation, while in the second experiment it is generated by a combination of translation and rotation. These test cases are designed to verify the accuracy and reliability of the proposed numerical scheme. In the future, the method can be naturally extended to three-dimensional problems, making it particularly suitable for modeling the local and global Earth’s gravity field.

How to cite: Macák, M., Minarechová, Z., and Mikula, K.: A DDFV-Based Approach to Oblique Derivative Boundary Value Problems with Applications in Geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3741, https://doi.org/10.5194/egusphere-egu26-3741, 2026.

The least-squares method is commonly used to estimate the parameters of a known mathematical model with a single functional form. However, in many applications, the underlying behavior is better approximated by piecewise functions composed of multiple segments. Such problems are usually addressed by empirically selecting the breakpoints and then applying a constrained least-squares method. This manual selection, nevertheless, does not always guarantee a globally optimal solution. In this work, a methodology for the simultaneous estimation of the function parameters and their breakpoints is developed. The proposed approach combines the method of indirect measurements with constraints and the Newton–Raphson method. Specifically, the breakpoints are treated as unknowns in the Newton–Raphson procedure and as parameters in the least-squares formulation. As the breakpoint estimates converge, the least-squares solution is progressively guided toward the optimal solution. Furthermore, all measurement equations retain a fixed functional structure that is piecewise-defined, enabling automatic partitioning of the measurements within the least-squares procedure. Finally, numerical examples are presented to demonstrate the proposed methodology.

How to cite: Koci, J. and Panou, G.: Least-squares fitting of piecewise curves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3790, https://doi.org/10.5194/egusphere-egu26-3790, 2026.

Solar system bodies such as planets, asteroids, and comets are increasingly becoming targets of satellite missions. These bodies typically exhibit irregular shapes, and generating shape models using spherical harmonics can be valuable for studying their physical properties. Beyond geodesy, spherical harmonic modeling is widely used in other scientific fields, including physics, geophysics, climate and weather science, medical imaging, chemistry, and engineering. In this work, we present two methods for generating shape models, a process commonly referred to as spherical harmonic analysis and synthesis. First, the classical least-squares method is introduced, both in its basic formulation and in combination with auxiliary algebraic techniques. Second, the well-known Neumann method is employed to compute the spherical harmonic coefficients. The aim of this study is to evaluate and compare these methods in terms of precision, computational efficiency, and simplicity. Finally, the performance of both approaches is demonstrated through numerical applications to celestial bodies.

How to cite: Panou, G., Koci, J., and Pappa, A.: Generation of a shape model in terms of spherical harmonics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5612, https://doi.org/10.5194/egusphere-egu26-5612, 2026.

This study presents high-resolution global gravity field modelling using the boundary element method (BEM), method of fundamental solutions (MFS) and singular boundary method (SBM). All three methods are applied to get numerical solutions of the fixed gravimetric boundary-value problem (FGBVP) which represents an exterior oblique derivative problem for the Laplace equation. In case of BEM, its direct formulation is applied to get the boundary integral equations that are numerically discretized using the collocation with linear basis functions. It involves a triangulated discretization of the Earth's surface considering its complicated topography.
   MFS is a mesh-free method which avoids a numerical integration of the singular fundamental solution introducing a fictitious boundary outside the domain, i.e. below the Earth's surface, where the source points are located. In MFS, the fundamental solution of the Laplace equation plays the role of its basis functions. We present how a depth of the fictitious boundary influences accuracy of the obtained MFS solution on the Earth's surface. In case that the source points are located directly on the Earth's surface, the ideas of SBM are applied to isolate singularities of the fundamental solution and its derivatives.
   Numerical experiments present high-resolution global gravity field modelling using BEM, MFS and SBM. All three methods are applied to reconstruct a harmonic function, namely the EGM2008 model up to degree 2160. At first, EGM2008 is reconstructed on the reference ellipsoid, and then on the discretized Earth’s surface. In all cases, the colocation/observation points are located with the same high-resolution of 0.075 deg. Comparisons of the obtained numerical solutions show that all three methods provide almost the same results when reconstructing EGM2008 on the ellipsoid.  When solving FGBVP on the discretized Earth’s surface, the BEM numerical solution gives the best result, then SBM and finally MFS. In all cases, the largest residuals are in high mountains of Himalayas and Andes, however, they are much smaller in the BEM solution due to a special treatment of the oblique derivative problem.

How to cite: Čunderlík, R. and Minarechová, Z.: BEM, MFS and SBM applied for global gravity field modelling – comparison of their numerical solutions on an ellipsoid and the discretized Earth’s surface, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6710, https://doi.org/10.5194/egusphere-egu26-6710, 2026.

The mathematical apparatus of integral transformations is often used for gravitational field modelling. A basic assumption of these integrals is the knowledge of relatively accurate data available globally. Practically, however, global data coverage is rarely achieved, and measurement errors always contaminate data. Therefore, integral transformations are appropriately modified and practical integral estimators are formulated and further employed in numerical experiments. In addition, corresponding statistical characteristics are often desired to indicate the quality of calculated gravitational fields. 
In this contribution, we systematically formulate practical integral estimators and their respective errors. We present the practical integral estimators in two forms: combined (i.e., combining the restricted integrals for near-zone effects and the truncated spherical harmonic series for far-zone effects) and as a spherical harmonic series. The practical integral estimators form a theoretical basis for an accurate gravitational field modelling, e.g. when solving upward or downward continuation. By employing a unified notation, the mathematical formulas are derived to an unprecedented extent for a broad class of quantities. Namely, the theoretical formulations connect four types of boundary conditions with twenty computed quantities. Point-wise errors and global mean square counterparts complement the practical integral estimators. The point errors can be calculated from the errors of the near-zone and far-zone boundary values, the position of the computational point, the size of the integration radius, and the maximum spherical harmonic degree of the far-zone effects. The number of variables is reduced for the global mean square errors, as they are invariant with respect to the horizontal position of computational points. Both statistical characteristics may also be employed in optimisation problems and experimental designs. The basic principles and formulations presented here can be applied to related problems in other potential fields, such as electrostatics or magnetism.

How to cite: Šprlák, M., Belinger, J., Pitoňák, M., and Novák, P.: Practical Integral Estimators for Gravitational Field Modelling: Basic Formulations and Statistical Characteristics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7879, https://doi.org/10.5194/egusphere-egu26-7879, 2026.

The poster presents the modeling of the gravitational field of the near-earth asteroid 101955 Bennu using two spectral-domain methods based on spherical harmonics and two numerical spatial-domain approaches. Due to its irregular shape, accurate gravitational field modeling represents a challenging task that is essential for precise orbit determination and spacecraft navigation. A mutual comparison of spectral- and spatial-domain methods is therefore vital. The spherical harmonic methods rely on two distinctive approaches. The first one is known as spectral gravity-forward modelling and produces a spherical harmonic series that is valid only outside the smallest sphere completely encompassing bennu. The second approach estimates an external spherical harmonic series from surface gravitational data using the least-squares method, making the series valid everywhere on and above the surface of bennu. Opposed to the spherical harmonic methods, two numerical approaches based on the finite element method are considered: the first solves the exterior boundary value problem (BVP) for the Laplace equation, while the second addresses a coupled interior–exterior BVP for the Poisson equation. Constant mass density is assumed in all experiments.

In the theoretical part of the poster, the fundamental principles of all applied methods are introduced. These approaches are subsequently implemented and tested in a series of numerical experiments. In the first experiment, gravitational acceleration evaluated on an approximated surface of the asteroid by spatial-domain gravity-forward modeling is prescribed as a boundary condition.

The convergence of the numerical solution toward the reference solution obtained from spherical harmonic functions is then analyzed. In the second experiment, a triangulated surface representation of the asteroid bennu is employed in order to assess the performance of the numerical methods on a more realistic geometry. The comparison focuses on the convergence rate, computational efficiency, and memory requirements of the individual approaches, providing insight into their applicability for gravitational field modeling of irregular small bodies.

How to cite: Minarechová, Z., Bucha, B., and Macák, M.: A comparative study of gravitational field modeling for 101955 Bennu, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9207, https://doi.org/10.5194/egusphere-egu26-9207, 2026.

How to cite: Abbasi, M. A.: Surface Variations in Earth's Time Variable Gravity Field Modelled by the Finite Element Method, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9360, https://doi.org/10.5194/egusphere-egu26-9360, 2026.

Besides the widely used Taylor expansion for analytical functions there is more complex form to represent some different expansions using the rational function [P^L/Q^M] in the form of relation of the two polynomials P and Q of degrees L for numerator and M for denominator.
The convergence rate of such an approximation is faster than of the ordinary Taylor expansion, while the coefficients of Padé approximation are calculated based on the Taylor expansion.

For example, let show the possibilities of the Padé approximations for expansion of the elliptical integrals, let's consider the well-known length X of an meridian arc from equator to geodetic latitude B on the reference ellipsoid with semi-major axis a and eccentricity e.

After standard Taylor expansion and integration we obtain expansion up to 11th degree:

The corresponding Padé approximation:

Regardless of the coefficients in front of the powers of the cosine of the latitude, 
we can see that the maximum order of the cosine of the latitude reaches only 4.

Taking for example the ellipsoid WGS-84 we get the length of meridian arc form equator to latitude 89 degrees:

precise (numerical integration): 9890270.31374637 m,

by formula (*):          9890270.31374637 m,

by formula (**):         9890270.31374636 m.

We see that using of the two polynomials of lower degree (max 4) provide the same accuracy than the usual expansion up to 11 degree!

There are possibility to develop the method using special type of Padé approximations for the

- orthogonal functions, and in particular

- orthogonal polynomials.

In physical geodesy the Padé approximations could be used in the 

- representing of the normal field characteristics, expanded into Taylor series, e.g. length of the coordinate line of the spheroidal system used in normal height calculation,

- gravity field modelling using Padé approximations with orthogonal functions,

- solving of the integral Fredholm equation of the second type by successive approximations.

The deficiencies of this method are related to the poles - points where the denominator turns into zero.

Literature:

G.A. Baker, P. Graves-Morris. Padé approximations. Part 1: Basic theory. Encyclopedia of Mathematics and its applications, Addison-Wesley, Reading, 1981.

How to cite: Popadyev, V., Dergileva, A., and Rakhmonov, S.: Using of Padé approximations in mathematical and physical geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12401, https://doi.org/10.5194/egusphere-egu26-12401, 2026.

The structure of the Laplace operator is relatively simple when expressed in terms of spherical or ellipsoidal coordinates. The physical surface of the Earth, however, substantially differs from a sphere or an oblate ellipsoid of revolution, even if optimally fitted. The same holds true for the solution domain and the exterior of a sphere or of an oblate ellipsoid of revolution. The situation is more convenient in a system of general curvilinear coordinates such that the physical surface of the Earth (smoothed to a certain degree) is embedded in the family of coordinate surfaces. Therefore, a transformation of coordinates is applied in treating the gravimetric boundary value problem. The transformation contains also an attenuation function. Tensor calculus and its rules are used and the Laplace operator is expressed in the new coordinates. Its structure becomes more complicated now. Nevertheless, in a sense it represents the topography of the physical surface of the Earth. Subsequently the Green’s function method is used together with the method of successive approximations in the solution of the gravimetric boundary value problem expressed in terms of the new coordinates.

How to cite: Holota, P.: Laplace’s operator with a structure reflecting the solution domain geometry and its use in the determination of the disturbing potential by a convergent series of successive approximations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14574, https://doi.org/10.5194/egusphere-egu26-14574, 2026.

Global gravity fields are traditionally represented using linear combinations of spherical harmonic basis functions, whose coefficients encode the geophysical signal. While this formulation is theoretically well-founded and guarantees universal approximation on the sphere, achieving high accuracy for high-frequency features requires spherical harmonics of very high degree, leading to a rapidly increasing number of parameters and substantial computational cost. As an alternative, recent works have shown that neural networks and numerical methods can represent gravity fields by learning coordinate-to-field mappings directly, often achieving competitive accuracy with fewer parameters.

In this work, we investigate storing the gravity field implicitly as neural network weights, using spherical harmonic expansions as input to sinusoidal representation networks (SIRENs), enabling a nonlinear mapping of gravity field components. Unlike classical linear spherical harmonic models, this hybrid approach does not rely on the full harmonic basis for field reconstruction; instead, it achieves accurate representations using fewer spherical harmonics, with the network’s nonlinearity compensating for the reduced expansion. Thus, the aim of this research is to compare the performance and efficiency of this hybrid approach versus the classical spherical harmonics expansion with respect to the Earth’s gravity modeling problem. 

To create a reference ground truth to approximate, we generate high-resolution acceleration data from the EGM2008 gravity model, sampling 5,000,000 points on an equal area grid for training, and 250,000 points on a Fibonacci grid for testing; both at EGM’s reference sphere. We remove the contribution associated with planetary oblateness to isolate higher-degree features. Using this dataset, we systematically evaluate a range of model complexities.

Results show that, for lower total parameter counts, the hybrid approach achieves a lower approximation error than the standard spherical harmonic expansion. Beyond a certain model complexity, a crossover behavior is observed, after which the standard spherical harmonic expansion surpasses the hybrid representation. This is consistent with increasing representational redundancy in the nonlinear network at high model complexity, whereas the classical spherical harmonic expansion allocates parameters efficiently through its orthogonal basis functions. 

The location of this break-even point is strongly influenced by the number of input spherical harmonics. In particular, a hybrid configuration using spherical harmonics up to degree L = 15 in the first layer combined with a six-layer SIREN consistently achieves lower approximation error in the test dataset than purely linear spherical harmonic models for parameter counts up to approximately 200,000, corresponding to a linear expansion up to degree 446. For inference on 250,000 samples, the equivalent linear spherical harmonic model takes 205.872 s, while the hybrid approach requires only 0.028 s, highlighting the computational efficiency of the method. 

Compared to purely coordinate-based neural networks, the hybrid model achieves better accuracy for similar parameter budgets. These results suggest that hybrid spherical harmonic–neural models offer an attractive trade-off between accuracy, parameter efficiency, and computational cost for global gravity field modeling. This study considered only 2-dimensional fields without an explicit radial component. Extending the hybrid representation to upward continuation and evaluation of functionals in 3D space is a direction for future work.

How to cite: Restrepo Berrío, J. D., Kusche, J., Springer, A., and Rußwurm, M.: Investigating Hybrid Spherical Harmonic–Neural Network Models for Efficient Functional Approximation of the Global Gravity Field Representation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14971, https://doi.org/10.5194/egusphere-egu26-14971, 2026.

The precise determination of the Earth's gravity field and geoid represents a fundamental challenge in physical geodesy, with direct implications for navigation, mapping, and geodynamic studies. Geostatistical simulation provides a rigorous methodological framework for addressing the spatial heterogeneity of gravimetric data and quantifying uncertainties associated with geodetic models. This study presents geostatistical applications in physical geodesy along three main axes: optimal interpolation of gravity anomalies through kriging and its variants, geostatistical simulation for probabilistic gravity anomalies modeling, and geodetic network optimization for geoid calculation. Geostatistical methods are distinguished by their ability to explicitly model spatial correlation through the variogram and rigorously quantify spatial uncertainty. Practical applications demonstrate effectiveness in integrating multi-source data with heterogeneous precision and resolution (terrestrial, airborne, and satellite measurements), propagating uncertainty in derived quantities, and optimizing the positioning of new gravimetric stations according to objective statistical criteria. Current challenges include processing very large datasets requiring high-performance algorithms and low-rank approximations, modeling anisotropy and non-stationarity of the gravity field, and extending to spatio-temporal approaches to capture temporal variations. Promising perspectives lie in hybridization with machine learning for automatic estimation of complex variograms while preserving the theoretical rigor of geostatistics, establishing this approach as an indispensable complement to classical methods in physical geodesy.

Keywords: gravity field, physical geodesy problems, geostatistical simulation, spatial interpolation, uncertainty quantification.

How to cite: Benikhlef, I.: Application of geostatistical simulation to gravity field modeling and physical geodesy problems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16144, https://doi.org/10.5194/egusphere-egu26-16144, 2026.

Integral transformations derived from boundary-value problems (BVPs) of potential theory constitute the core mathematical apparatus of physical geodesy and gravity-field modelling. Classical Green’s function solutions of the Dirichlet, Neumann, and Stokes problems generate a complete family of integral transformations that relate the disturbing gravitational potential and its directional derivatives. In the spherical approximation, this framework—summarised by the Meissl scheme—has reached a high level of completeness and currently provides mutual transformations among all components of the gravitational-gradient tensors up to the third order. These tools underpin the processing of heterogeneous gravity observations acquired by terrestrial, airborne, and satellite sensors.

Increasing accuracy requirements and the geometric proximity of the Earth to a rotational ellipsoid, however, necessitate a transition from spherical to spheroidal formulations. Although analytical solutions of the three fundamental BVPs on an oblate spheroid have been derived and several corresponding integral equations have been proposed, the spheroidal analogue of the Meissl scheme remains incomplete.

In this contribution, we derive spheroidal integral formulas for computing the disturbing gravitational potential and its first-, second-, and third-order directional derivatives from the disturbing potential and its vertical and horizontal derivatives. The correctness of the newly derived integral formulas is verified by closed-loop tests using data from a global geopotential model.

How to cite: Pitonak, M., Belinger, J., Novak, P., and Sprlak, M.: Spheroidal integral formulas for computing the disturbing gravitational potential and its first-, second- and third-order directional derivatives from disturbing gravitational potential  and its vertical and horizontal derivatives , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16392, https://doi.org/10.5194/egusphere-egu26-16392, 2026.

The determination of gravitational fields generated by planetary bodies represents a fundamental task in modern geodesy. To facilitate the computation of gravitational field functionals, we approximate the shapes of individual planetary bodies. The spherical approximation is the most popular, as it conveniently employs numerous symmetries of the sphere. Generally, however, planetary bodies are flattened at the poles or even at equators. Therefore, a conceptual framework on the spheroidal approximation should be analysed.

In this contribution, we develop a new mathematical theory for modelling gravitational fields generated by irregular bodies. Specifically, the gravitational potential, the components of the gravitational gradient and the second- and third-order gravitational tensor components are parametrised using spheroidal harmonic functions defined within the minimal Brillouin spheroid.

To enable global calculation, especially near the poles, the original spheroidal harmonic expansions are transformed into their non-singular counterparts.  Additionally, we investigate selected numerical aspects of the Legendre functions of the first and second kind. Numerical experiments are performed to validate the proposed approach. Both singular and non-singular formulations are systematically evaluated.

How to cite: Belinger, J., Dohnalová, V., Pitoňák, M., Šprlák, M., and Novák, P.: Numerical aspects of gravitational field modelling using spheroidal harmonic functions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16758, https://doi.org/10.5194/egusphere-egu26-16758, 2026.

Airborne gravimetry plays a critical role in local gravity field determination but remains costly and operationally constrained. In current practice, gravity data collected during takeoff, landing, and turning (collectively referred to as preparing time) are routinely discarded due to sensor degradation under dynamic motion. These phases, however, constitute a substantial fraction of total flight time and represent a largely untapped data source. This study investigates the potential benefits of incorporating gravity observations from the entire flight trajectory to enhance local gravity field modeling.

Numerical simulations were first conducted to evaluate the impact of using full-flight gravity data under varying noise conditions and spectral bandwidths. Gravity disturbances synthesized from EGM2008 were downward continued using radial basis functions. Results show that including preparing-time data improves modeling precision by up to 67% within the spherical harmonic degree band [200, 1080] and up to 61% when extending the bandwidth to [200, 2160], consistently across different noise scenarios. The feasibility of this approach was further demonstrated using real scalar gravimeter data from the GRAV-D survey. Preliminary results of incorporating these recovered observations into an airborne-only local quasi-geoid model shows promising geoid model improvements when compared with GNSS/Leveling bench marks.

In addition to the completed work, ongoing research is exploring the integration of onboard inertial measurement unit (IMU) data, to which access has recently been obtained. Preliminary analyses reveal strongly correlated error patterns in the preparing-time gravity observations that appear closely linked to aircraft attitude variations. The availability of roll and pitch measurements from the IMU opens the possibility of analytically mitigating these errors through physical modeling, potentially reducing reliance on purely data-driven approaches.

Additional simulations indicate that achieving 1 mGal-level gravity precision during dynamic flight requires roll and pitch angle accuracies better than 5 arc-minutes, underscoring the importance of accurate attitude information. Overall, the results highlight significant untapped potential in airborne gravimetry and suggest a paradigm shift toward exploiting full flight trajectories. As emerging technologies such as vector gravimetry, cold-atom sensors, and advanced inertial systems continue to mature, the systematic integration of dynamic-flight data is expected to further enhance the accuracy and efficiency of future airborne gravity surveys.

How to cite: Li, X.: Exploiting Full Flight Trajectories in Airborne Gravimetry: From Simulation to Real-World Validation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22219, https://doi.org/10.5194/egusphere-egu26-22219, 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.

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.

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.

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.

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 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 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.

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 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 6^th, 8^th, 11^th and 12^th 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 8^th,11^th  and 12^th  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.

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 11^th, 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 Atomic Clock Ensemble in Space (ACES) was launched to the International Space Station (ISS) on 21^st 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.

Global Navigation Satellite Systems (GNSS) are based on measuring signal propagation time, so that clock information is required for both the transmitting satellite and the receiving ground station. For Precise Point Positioning (PPP), synchronization errors of the receiver clock are usually estimated as epoch-wise biases with white noise as stochastic behavior. A major issue for the receiver clock estimates is the high correlation with the station height and the tropospheric zenith delay that results from the observation geometry. Introducing models to reduce the number of unknown clock parameters is one way to mitigate these correlations. However, adequate modeling requires a high degree of stability for the corresponding clock.

In this contribution, we show the results of modeling highly stable GNSS receiver clocks in PPP using piece-wise linear representations. We discuss different options to control the deterministic and stochastic part of the piece-wise linear model (interval length, parameter weighting, etc.). For 56 highly stable hydrogen maser (H-maser) stations of the International GNSS service (IGS), the impact of piece-wise linear clock modeling on correlated parameters, especially the sub-daily height estimates, is presented. The differences in the modeling impact of the individual receiver clocks are explained by categorizing the stations based on statistical and observational quality measures. In addition, the effects of individual processing options (used GNSS constellations, elevation cutoff angle) are shown.

How to cite: Widczisk, J. S., Männel, B., and Wickert, J.: Piece-wise linear clock modeling for highly stable IGS H-maser stations in Precise Point Positioning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3083, https://doi.org/10.5194/egusphere-egu26-3083, 2026.

Accurate estimation of GNSS station velocities requires careful consideration of the stochastic properties of their position time series, which are commonly affected by white and flicker noise. In this study, we propose a non-parametric approach combining Singular Spectrum Analysis (SSA) with an adaptive Monte Carlo SSA (MC-SSA) to estimate station velocities and their uncertainties, explicitly accounting for the noise spectrum. Using SSA, the trend and seasonal components are removed from the analyzed GNSS time series, after which the residual noise is analyzed using Welch’s spectral method to identify its noise type. Monte Carlo simulations are then employed to generate synthetic realizations of white and/or flicker noise according to the detected type, and the trend is reconstructed with SSA for each realization.

The proposed methodology is applied to daily position time series from 28 International GNSS Service (IGS) stations located on the African plate. The data are expressed in the local topocentric reference frame (North, East, Up), referenced to ITRF2020, and cover the period from 1999 to 2026. The results show that the average velocities of the analyzed stations are about 17.625, 19.446, and -0.749 mm/yr in the North, East and Up components, respectively. For stations whose position time series are dominated by white noise, the uncertainties associated with the estimated horizontal and vertical velocities range from 0.001 to 0.027 mm/yr and from 0.010 to 0.086 mm/yr, respectively. In contrast, the velocities affected by flicker noise exhibit a significantly larger uncertainty, varying from 0.045 to 0.260 mm/yr for the horizontal components and from 0.148 to 0.628 mm/yr for the vertical component. The proposed MC-SSA approach was validated using synthetic GNSS position time series generated with prescribed velocities and well-defined noise characteristics, spanning the same time intervals as the used data. The results demonstrate that MC-SSA yields velocity estimates that are very close to the simulated values and provides more realistic uncertainty estimates than ordinary least squares solutions. Moreover, this study provides a consistency assessment of velocities from regional GNSS stations on the African plate through comparison with nearby IGS stations in the ITRF2020 reference frame.

How to cite: Khelifa, S., Dekkiche, H., Allal, S. H., and Ahmed Betchim, Y.: GNSS Velocity Estimation Using Adaptive Monte Carlo SSA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4454, https://doi.org/10.5194/egusphere-egu26-4454, 2026.

The contribution of the International Laser Ranging Service (ILRS) to the latest International Terrestrial Reference System (ITRS) realizations is based on Satellite Laser Ranging (SLR) observations of just four spherical satellites (LAGEOS-1/2 and Etalon-1/2). Since 2025, one more spherical satellite (LARES-2) is used by the ILRS to determine global geodetic parameters such as coordinates and velocities of globally distributed SLR stations and Earth Rotation Parameters (ERP), namely x- and y-pole coordinates and length of day (LOD). However, SLR observations to eight more spherical satellites (Starlette, Ajisaj, Stella, GFZ-1, WESTPAC, Larets, BLITS, LARES) and several altimetry satellites are available over an overall time span from 1976 with the total number of their SLR observations exceeding the number of SLR observations of the five presently used satellites by a factor of about five. Orbits of these satellites have various altitudes and inclinations and can be determined at the 1-2 centimeter level of accuracy. The long observational time series and the differing orbital characteristics of the satellites lead to an improved SLR observation geometry.

In this study, we investigate the potential of using SLR observations of seven altimetry satellites (TOPEX/Poseidon, Jason-1/-2/-3, Sentinel-3A/-3B/6A) for the determination of global geodetic parameters mentioned above, as compared to using SLR observations of five and 13 spherical satellites and in combination with them.

How to cite: Rudenko, S., Bloßfeld, M., Seitz, M., and Zeitlhöfler, J.: Determination of an SLR terrestrial reference frame and Earth Rotation Parameters from SLR observations to altimetry and spherical geodetic satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5480, https://doi.org/10.5194/egusphere-egu26-5480, 2026.

The European Space Agency’s (ESA) Genesis mission has been approved for launch in 2028. Its primary objective is to enhance the terrestrial reference frame by establishing a space tie on board the Genesis satellite that connects all space-geodetic techniques used for its realization.

Concerning the VLBI part of Genesis, new challenges arise from the fact that the VLBI broadband signal will be spread across multiple antennas on the satellite, each emitting in its own bandwidth. If this aspect is not corrected for with sufficient accuracy, the group delays will not refer to a well-defined reference point on the satellite.

In this study, we investigate how large the impact of neglecting such a correction or imperfectly modelling it would be on estimated parameters, such as station positions. We address this question by simulating observations to the Genesis satellite on the group delay level. Based on simulated 24-hour sessions, consisting of quasar and satellite observations, a full geodetic VLBI analysis is carried out, using the software VieVS-VLBI. Here we present our results and discuss the necessity of phase center corrections for VLBI observations to the Genesis satellite.

How to cite: Wolf, H., Jaron, F., and Böhm, J.: On the impact of imperfect models for multiple VLBI antennas on the Genesis satellite on the terrestrial reference frame, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7611, https://doi.org/10.5194/egusphere-egu26-7611, 2026.

Proper a priori knowledge of the phase center location and pattern of the GNSS antenna is an essential prerequisite for use of GNSS measurements in the determination of the terrestrial reference frame. This is well known for terrestrial GNSS stations, but likewise applies for space-borne GNSS tracking. In the context of the upcoming Genesis mission, the analysis of flight data from existing low Earth orbit (LEO) missions offering co-location of multiple space-geodetic instruments and their possible contribution to the TRF refinement has gained renewed interest. With this background, we investigate the quality of ground-based calibrations from the two most widely-used geodetic-grade LEO GNSS antenna types and compare these calibration with in-flight measurements for a range of scientific Earth observation missions. More specifically, we analyse the combination of an aviation patch antenna with JPL chokering using flight data from the GRACE, Jason-2/3, and TerraSAR-X satellites as well as the RUAG (now Beyond Gravity) patch antenna with integrated choke ring from GNSS observations of the GRACE-FO and Sentinel-3A/3B/6A satellites.

Overall, the analysis covers a period of at least 10 years and makes use of pre-computed precise GNSS orbit, clock, and bias products from the International GNSS Service for precise orbit determination of the LEO satellites. The analysis period includes different reference frames (IGSR3, IGS14, IGS20) to verify the consistency of changes in the estimated phase center offsets (PCOs) with TRF scale changes. Following a discussion of conceptual problems in the definition and measurements of "the" antenna phase center, we assess the expected uncertainty of LEO force models to characterize the expected stability of the dynamical reference frame of the various LEO satellites that serves as a reference for the PCO determination from in-flight observations. The results reveal notable discrepancies between ground calibrations and in-flight results, which obviously hamper the use of existing LEO GNSS data for independent TRF scale determination. These include notable phase pattern distortions attributed to the impact of the local antenna environment as well as systematic PCO differences, which can only partly be attributed to center-of-mass uncertainties. In the context of Genesis, adequate measures need to be taken to avoid launch-related structural deformations changing the center-of-mass location from the design values and to calibrate the GNSS antenna characteristics after satellite integration in a flight-representative configuration.

How to cite: Steigenberger, P. and Montenbruck, O.: Comparison of LEO GNSS antenna phase characteristics from ground and in-flight calibrations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8224, https://doi.org/10.5194/egusphere-egu26-8224, 2026.

DTRF2020, the latest realization of the ITRS calculated by DGFI-TUM, has been updated with two new solutions, DTRF2020-u2023 and DTRF2020-u2024. They contain additional observation data of the four contributing techniques, VLBI SLR, GNSS and DORIS, from three and four years, respectively.

We present the results of these two DTRF updates and discuss the challenges associated with performing annual updates in comparison with calculating new DTRF solutions every five to six years.

In early 2026, the ITRS Center requested new contributions from the IAG Technique Services for the third update, covering data up to the end of 2025. Where new time series are already available, we present initial analysis results, focusing in particular on the datum parameters.

How to cite: Seitz, M., Bloßfeld, M., Zeitlhöfler, J., Angermann, D., Klug, J., Reber, M., and Seitz, F.: The DTRF2020 Updates: DTRF2020-u2023 and DTRF2020-u2024, and Preparation of the Third Update, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9773, https://doi.org/10.5194/egusphere-egu26-9773, 2026.

As one of the four space geodetic techniques, the Global Navigation Satellite System (GNSS) has been playing an increasingly important role in determining high-quality geodetic parameters, including the Earth rotation parameters (ERPs) and geocenter coordinates (GCCs). In addition to GNSS observations from ground station networks, GNSS observations from low Earth Orbit (LEO) satellites can serve as an important supplement to improve the estimation of geodetic parameters. Over the past decade, with the proposal and validation of the concept of LEO constellation-enhanced GNSS, several LEO navigation-augmentation constellation projects are being planned or constructed. Unlike traditional LEO satellite missions, LEO constellations are not only equipped with onboard receivers but also broadcast downlink navigation signals, establishing a direct link between the LEO satellites/constellations and station fixed on the Earth’s surface. The emergence of LEO navigation-augmentation constellations provides a new technological means for geodetic parameters determination and performance enhancement.

In this study, we focus on the determination of global geodetic parameters using LEO constellation and its potential enhancement to GNSS. We begin with the effect of different orbital configuration on the estimation of ERP and GCC with LEO downlink observations. Different LEO constellations, with different orbital inclination, number of orbital planes, and altitude are designed, and their performance is comparatively analyzed. For LEO orbital inclination, Walker Delta (108/9/0) constellations are designed, with the orbital inclination varying from 45° to 90°. The results indicate that the performance of ERP and GCC estimation is optimal for inclinations 65°-75°. Meanwhile, the increase of the number of orbital planes is demonstrated to be beneficial for geodetic parameters estimation, under scenarios where either the number of satellites per plane or the total number of LEO satellites is fixed. What’s more, when the orbit altitude increases from 500 to 2000 km, the formal errors of ERP and GCC estimates decrease, which is mainly due to the increased number of satellites observed by the ground stations. Nevertheless, the Root Mean Square (RMS) values of length of day (LOD) and GCC reach the minimum at the altitude of approximately 1500 km.

Based on the better-performed LEO constellation (Walker: 144/12/0, orbital altitude: 1500 km), the potential enhancement to GNSS is further investigated. The results indicate that with downlink observations, GNSS and LEO constellation exhibit different capabilities in ERP and GCC estimation, i.e., GNSS performs better in ERP estimation, while LEO constellation is superior in GCC estimation. The GPS+LEO combined solution makes the smallest formal errors, which are 4.21 uas for polar motion, 9.94 uas/d for polar motion rate, 0.64 us/d for LOD, and (0.14, 0.34) mm for the X/Y and Z component of GCC, presenting improvement of 8.1%-75.5% over GPS-only solution. At the same time, the combined solution also improve the accuracy by 10.4%, 56.5%, 62.8%, and 84.7% for polar motion, polar motion rate, LOD, and GCC, respectively, compared with the GPS-only solution.

How to cite: Cheng, Y., Li, X., Zhang, K., Zhao, Y., and Li, Y.: Determination of global geodetic parameters using low Earth orbit constellation: performance analysis and its potential enhancement to GNSS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11970, https://doi.org/10.5194/egusphere-egu26-11970, 2026.

Geocenter motion can be derived through various space geodetic techniques and hydrological models using different methods, such as direct and inverse. Each technique suffers from specific issues associated with a sparse observing network, orbit modeling errors, or limited sensitivity of the observing techniques to particular components of the geocenter motion, especially to the Z component. Modeling issues result in the spurious signals observed in the time series of the geocenter motion, such as the draconitic periods, orbit resonance terms, and tidal aliasing signals.

No official combined products currently exist for the geocenter motion and low-degree gravity field coefficients. Hence, different geocenter models are employed in various applications, such as altimetry, the analysis of GNSS station motions, or GRACE-based gravity field studies.

We propose a combination and comparison campaign for the geocenter motion and low-degree gravity field parameters. The first step of the campaign includes technique-specific combinations, such as GNSS-only, DORIS-only, SLR-only, LEO-only, and a confrontation with hydrological models. In the second step, the system-specific solutions will be compared and combined, considering different methods of deriving geocenter motion, including the network shift approach, deriving degree-1 gravity field coefficients, and inverse methods based on surface load displacements, as well as GRACE-derived products supported by geophysical models. The following step will consist of the combination of low-degree gravity field coefficients using the variance component estimation (VCE) technique and other combination techniques to separate system-specific signals from those signals that have geophysical justification. Finally, the combination will be applied to the low-degree gravity field harmonics to expose software-specific issues in SLR-based values, as well as differences between the values obtained from SLR, GRACE, LEO satellites, and inverse methods applied to a dense GNSS network.

How to cite: Sośnica, K., Nowak, A., Kur, T., Gałdyn, F., and Zajdel, R.: Analysis and Combination of Geocenter Motion and Low-Degree Gravity Field Parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12208, https://doi.org/10.5194/egusphere-egu26-12208, 2026.

How to cite: Dumitraschkewitz, P. and Mayer-Gürr, T.: Analysis of estimating PCO/PCV using raw observationa approach in global GNSS processing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12347, https://doi.org/10.5194/egusphere-egu26-12347, 2026.

The Federal Agency for Cartography and Geodesy (BKG) is currently taking part in the research project GENESIS-D (a consortium of the main German geodetic institutes). The goal of this project and our studies therein is to be able to consistently process, combine and validate observation data of ESA’s upcoming Genesis mission in the future. Genesis will allow, for the first time, the co-location in space of all four main space geodetic techniques, namely VLBI, SLR, GNSS, and DORIS. The orbit combination will enable a quantification of inter-technique systematic discrepancies, and will increase the inter-technique consistency during the determination of the international terrestrial reference frame (ITRF). Already now, several Low-Earth-Orbiting (LEO) satellites represent a co-location in-space for the three satellite-based space-geodetic techniques, i.e., GNSS, SLR and DORIS. Using such LEOs allows to study potential hurdles in harvesting the full potential of Genesis and preparing the analysis and combination software to fully exploit satellite co-locations.

In this work, we have chosen the altimetry satellite Sentinel-6A Michael Freilich (S6A) as a proxy for Genesis in order to conduct research and software development regarding the combination of SLR and GNSS. For now, SLR data to S6A and to the SLR specific satellites LAGEOS-1 and LAGEOS-2 have been analyzed.

For the two cannonball-shaped LAGEOS satellites we estimate weekly arcs, whereas for S6A daily arcs are set up, due to the lower altitude and more complicated radiation-pressure modelling. By accumulating the daily arc S6A normal equations (NEQs) into weekly NEQs and stacking them with the LAGEOS-based NEQs, we obtain weekly solutions that include satellite orbits, station coordinates, Earth rotation parameters, geocenter coordinates, and SLR range biases. We compare all parameters estimated in the framework of the three solution types, that are (i) LAGEOS-only; (ii) S6A-only; and (iii) LAGEOS+S6A.

We find that the station coordinate repeatability for (i) LAGEOS is better than for (ii) S6A, which is expected given the use of a single-satellite LEO solution. Generally, the single-satellite solution of (ii) S6A yields worse results compared to the other two solutions as these are multi-satellite solutions. On the other hand, the advantage of S6A shows up, e.g., in the six-fold increase in low-elevation observations to S6A compared to LAGEOS, which facilitates the decorrelation between range bias and station height. The analysis of the impact of S6A data on the global LAGEOS solution offers insight into the potential impact that Genesis will have on current SLR products. It also ensures the early identification and resolution of software issues, allowing Genesis data to be evaluated from the outset of the mission. This study will be expanded in the future by a global GNSS solution as well as GNSS analysis of S6A data, as well as the subsequent combination with SLR.

How to cite: Weinem, L., Balidakis, K., Flohrer, C., Thaller, D., Kehm, A., König, D., Arnold, D., Meyer, U., and Geisser, L.: Integration of space-based co-locations for enhanced reference frames: Investigating the Potential of ESA’s Genesis Mission , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12473, https://doi.org/10.5194/egusphere-egu26-12473, 2026.

The fundamental reliance of GNSS on one-way signal travel time measurements necessitates precise clock synchronization. This introduces high correlations between satellite/receiver clock offsets and nearly all other estimated parameters—such as station coordinates, tropospheric delays, and orbital elements—creating a fundamental bottleneck in modern high-precision geodesy by limiting the independent determinability of these parameters.

Recent breakthroughs in time-frequency technology offer promising pathways to mitigate this issue. Ultra-stable optical clocks and fiber-optic time transfer have emerged as transformative tools. Fiber-optic links can synchronize the clocks of GNSS receivers to a remarkable degree, achieving fractional frequency stability of clock difference at the 10^-18 level—several orders of magnitude beyond GNSS-based synchronization. Consequently, receivers connected via fiber can be treated as sharing a common clock. In parallel, highly stable hydrogen masers, already deployed at many permanent GNSS stations, provide another foundation for common-clock processing. When two receivers are each equipped with a hydrogen maser, the stability of their clock offset difference can approach that achievable via fiber links, effectively constituting a "virtual" common clock even in the absence of a physical connection.

To leverage these advancements, we developed and implemented a novel module that incorporates common-clock constraints into the widely used Bernese GNSS Software. This module enforces that multiple receivers share a single common clock parameter per epoch. Initial processing results demonstrate that applying this constraint significantly reduces noise in key estimated parameters, notably in station height time series and high-frequency (e.g., 10 to 30 minutes) tropospheric delay estimates.

The implementation of a common-clock framework opens several avenues for future enhancement of GNSS. Beyond reducing parameter noise through decorrelation, it raises the prospect of establishing a more stable time reference for GNSS networks—potentially realized as a software-generated composite clock. This work represents a critical step toward integrating next-generation timekeeping infrastructure into global geodetic networks, with the goal of improving the stability of the terrestrial reference frame and the precision of all GNSS-derived geodetic products.

How to cite: Wang, Z. and Hugentobler, U.: Implementing a Common Clock Framework in GNSS: Harnessing Fiber-Optic Links and Global Hydrogen Maser Networks for Enhanced Parameter Estimation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12913, https://doi.org/10.5194/egusphere-egu26-12913, 2026.

The International DORIS Service (IDS) has contributed to the third annual update of the 2020 realization of the International Terrestrial Reference Frame (ITRF2020). As part of this effort, IDS has estimated DORIS station positions and velocities, as well as Earth Rotation Parameters (ERPs), using DORIS data. These computations are based on the latest weekly multi-satellite series from the five IDS Analysis Centers and an IDS Associated Analysis Center, covering data from 2025 and backward 2021. Note that for the first time, the IDS combined series will include daily LOD (Length-Of-Day) estimates.

The primary objectives of this study are to evaluate the DORIS contribution to this update of the ITRF2020 in terms of: (1) geocenter motion and scale, (2) station positions and week-to-week position repeatability, (3) ERPs, and (4) a cumulative position and velocity solution. A particular focus is placed on the LOD estimates and on the impact of including SWOT (Surface Water Ocean Topography) DORIS data.

How to cite: Moreaux, G., Lemoine, F., Capdeville, H., Štěpánek, P., Otten, M., Nahmani, S., Pollet, A., and Schreiner, P.: IDS contribution to the third update of the ITRF2020, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13383, https://doi.org/10.5194/egusphere-egu26-13383, 2026.

The adjustment of trajectory models to GNSS station position time series is an essential step in the establishment of terrestrial reference frames, but also in a wide range of geophysical studies investigating glacial isostatic adjustment, tectonics, or coastal sea-level change. This trajectory modelling step is complicated by the presence of occasional discontinuities in the time series, including outliers, mean offsets (jumps), and changes in velocity. With the increasing number and longevity of GNSS stations, traditional manual trajectory modelling of position time series by an experienced operator becomes increasingly time-consuming and even impossible for large datasets. For this reason, automatic discontinuity detection approaches are increasingly appealing for many geodetic and geophysical applications.

A central concern with automatic modelling approaches is their reliability. While past studies suggest that automatic approaches are less reliable than human experts, this situation may change with advances in artificial intelligence. One limitation to monitoring progress in automatic trajectory modelling is the absence of a standardized benchmarking approach for discontinuity-detection algorithms. In practice, each research group publishes performance measures based on different data sets of either human-labeled or synthetic time series. Unfortunately, data sets of human-labeled time series are limited in size and may be incomplete because humans are unlikely to detect the smallest discontinuities. Synthetic time series are not necessarily reliable either, as they may lack realism with respect to length, gaps, frequency and amplitude of discontinuities, and noise properties. To address these benchmarking issues, we will present a generator of realistic synthetic GNSS station position time series. Building upon the characterisation of real data sets, this generator will contribute to the development of a standardized benchmarking approach for automatic discontinuity detection algorithms. In the long run, this generator may also be employed to train new machine learning algorithms.

How to cite: Gobron, K., Bouvier, C., De Oliveira, A., Amal, S., and Rebischung, P.: Generating realistic synthetic GNSS station position time series to evaluate automatic discontinuity detectors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14154, https://doi.org/10.5194/egusphere-egu26-14154, 2026.

The International VLBI Service for Geodesy and Astrometry (IVS) provides a unique and fundamental contribution to the determination of the International Terrestrial Reference Frame (ITRF), most notably as a primary technique for defining the frame's scale. While the last comprehensive reprocessing of the VLBI data archive was conducted for the ITRF2020 submission, subsequent updates (u2023 and u2024) were limited to the addition of recent years.

For the ITRF2020-u2025 update, the IVS has undertaken a full reprocessing of the entire history of VLBI observing sessions. This decision was motivated by the identification of critical issues within the data archive: station naming inconsistencies and systematic errors in ionospheric corrections, which required the re-creation of some of the databases. Furthermore, the reprocessing incorporated several refined station-specific models, including newly determined gravitational deformation models and updated antenna axis offsets.

A major highlight of this reprocessing effort is the expansion of the included frequency bands to K-band (24 GHz). While previous ITRF submissions relied solely on legacy S/X-band and broadband VLBI Global Observing System (VGOS) sessions, this update integrates approximately 200 K-band VLBI sessions for the first time, comparable to the total number of VGOS sessions. Nevertheless, the legacy S/X-band network remains the dominant backbone of the contribution, encompassing about 7,600 sessions.

This contribution presents preliminary results of the IVS-combined solution, generated by the IVS Combination Center from individual Analysis Center contributions. We evaluate the quality of the resulting geodetic parameters, with a primary focus on the stability of station coordinates, terrestrial scale realisation, and the precision of EOP.  

How to cite: Soja, B., Kehm, A., Bachmann, S., Raut, S., Behrend, D., and Haas, R.: The Full Reprocessing Effort for the ITRF2020-u2025 Update by the IVS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15008, https://doi.org/10.5194/egusphere-egu26-15008, 2026.

The NASA GSFC/UMBC Joint Center for Earth Systems Technology (JCET) ILRS Analysis Center supports the International Laser Ranging Service (ILRS) through routine SINEX submissions, network validation, and contributions toward future updates of the International Terrestrial Reference Frame (ITRF). As an ILRS Analysis Center (AC) and the designated ILRS backup combination center (ILRS-B), JCET/NASA GSFC generates daily and weekly SINEX solutions and combines contributions from eight ILRS ACs to produce the ILRS-B solution, complementing the official ILRS-A solution provided by ASI for the ITRF Combination Centers (DGFI, JPL & IGN).

Since LARES-2 was launched in August 2022, ILRS Analysis Centers began generating v90-format solutions in April 2025, retroactively covering data from September 2022. These solutions incorporate LARES-2 tracking using the new Data Handling Format (DHF), improving geodetic coverage and supporting future reference frame updates. The v90 series will be reprocessed to apply updated mass corrections, include newly available stations, and reinstate sites previously quarantined during earlier processing cycles. This v90 SINEX will represent the core of our contribution to the development of ITRF2020-u2025, which will be based on a full reprocessing of SLR data from 2021.0 to 2026.0

In this paper, we provide information on the v80 & v90 series that contribute to this ITRF contribution. We summarize the impact of adding LARES-2 compared to the legacy geodetic satellite contributions from LAGEOS-1,2 and Etaton-1,2. We review the performance of the ILRS-B combination, in particular with respect to the station coordinates and Earth Orientation Parameters (EOPs).

How to cite: Kuzmicz-Cieslak, M., Evans, K. D., Belli, A., and Lemoiine, F. G.: NASA GSFC/JCET ILRS Analysis Center Contribution to ITRF2020-u2025 Development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15495, https://doi.org/10.5194/egusphere-egu26-15495, 2026.

Accurate satellite phase center offsets (PCOs) are critical for high-precision GNSS data processing. Their pre-launch calibration and on-orbit estimation have long been essential tasks. For the third-generation BeiDou Navigation Satellite System (BDS-3), however, recent studies often derive PCOs from precise orbit determination (POD) using GPS L1/L2 receiver antenna calibrations and adjustable box-wing models for solar radiation pressure (SRP) modeling. Due to differing processing strategies, estimated BDS-3 PCOs vary across studies. Leveraging BDS-3 satellite metadata and BDS-specific receiver antenna calibrations, this study estimates BDS-3 satellite PCOs using long-term data. Results indicate that the X-offset obtained with an empirical SRP model combined with BDS-3 metadata is the most stable. Further analysis shows that the Z-offset is highly sensitive to the type of receiver antenna calibration model used. The relationship can be approximated as follows: a network-averaged bias in the receiver antenna up-direction causes a change of approximately −22.7 times in the MEO Z-offset for BDS-3-only POD, and −28.6 times for combined BDS/GPS processing. This finding aligns with prior studies, despite methodological differences, underscoring the importance of precise receiver antenna calibration. Validation experiments comparing the manufacturer’s model with the newer model show an average improvement of nearly 3% in the RMS of overlapping orbit differences. Additionally, static precise point positioning (PPP) experiments demonstrate coordinate improvements of about 5% for B1I/B3I and 14% for B1C/B2a signals compared to results using the manufacturer’s model.

How to cite: Huang, C.: On-orbit estimation of antenna phase center offsets for BDS-3 satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16386, https://doi.org/10.5194/egusphere-egu26-16386, 2026.

Space-geodetic techniques rely on Earth orientation parameters (EOP) to relate satellite observations to terrestrial reference frames. While their importance for global consistency is well recognized, the sensitivity of satellite-based orbit determination to degraded Earth orientation information remains only partially quantified, particularly for techniques that depend on a combination of externally prescribed and internally estimated parameters.

In this contribution, we present a first assessment of the sensitivity of Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) geodetic products to degraded Earth orientation information. Using a standard DORIS processing configuration, in which UT1–UTC is prescribed from external products while polar motion can be estimated, we analyse how realistic perturbations applied to the Earth orientation time series propagate into observation residuals, orbital parameters, and empirical force modelling.

The study explores the extent to which DORIS solutions can accommodate degraded Earth orientation information through internal parameter adjustments, and examines the respective roles of different components of Earth rotation in this process.

This work provides initial insight into the robustness and limitations of DORIS-based geodetic products with respect to Earth orientation information, and contributes to a broader understanding of the dependence of satellite geodesy on high-quality geodetic products. As such, it provides technical elements relevant to the objectives of the United Nations Global Geodetic Centre of Excellence (UN-GGCE) in assessing the resilience and long-term sustainability of the global geodetic infrastructure.

How to cite: Nahmani, S. and Pollet, A.: Assessing the sensitivity of DORIS precise orbit determination to degraded Earth orientation information, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17706, https://doi.org/10.5194/egusphere-egu26-17706, 2026.

The Genesis mission of the European Space Agency (ESA) aims to provide near-continuous space ties among the four major space geodetic techniques. These ties are expected to help improve the accuracy and stability of the International Terrestrial Reference Frame (ITRF) by allowing the determination of inherent inter-technique biases. One of these techniques is Very Long Baseline Interferometry (VLBI). For Genesis, VLBI observations are planned to be made possible by emitting signals with an onboard VLBI transmitter, which can be observed using the VLBI Global Observing System (VGOS). 

Many technical and operational challenges are currently being addressed to make sure that VGOS can observe Genesis successfully. This is done through studies that rely on simulations or on experiments using non-Genesis-like satellites. So far, combining real and simulated data has been underutilised, even though it provides both realistic observation conditions and flexible scenario designs, which could be used to answer remaining open questions. Two examples of remaining challenges are the determination of how often Genesis should be observed without degrading the estimation of geodetic parameters and station positions, and the assessment of how and if Genesis observations can contribute to those estimates.

In this study we apply a hybrid approach of combining real and simulated data. The aim is twofold: first, we want to investigate the impact of reducing the number of quasar observations on real 24-hour VGOS sessions as if Genesis was being observed; and second, we want to assess real 24-hour VGOS sessions which include simulated Genesis observations that are partially based on real data. The latter is done by combining real quasar observations and simulated satellite observations that are based on estimates from the real quasar observations. We also investigate the estimation of the geocentre, which is possible due to the added simulated satellite observations.

How to cite: Wolfs, R. and Haas, R.: A Hybrid Approach Using Real and Simulated Data to Assess the Performance of VGOS Sessions with Added Genesis Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18316, https://doi.org/10.5194/egusphere-egu26-18316, 2026.

The objective of the future Global Geodetic Observing System (GGOS) to realize the terrestrial reference system (TRS) with 1 mm accuracy and 0.1 mm/yr long-term stability remains challenging when the four space geodetic techniques – GNSS, SLR, VLBI, and DORIS – are processed independently in the traditional, technique-specific manner. Key challenges arise from the sparse and highly inhomogeneous global distribution of co-location sites used to tie the individual solutions together, as well as from the treatment of technique-specific calibration parameters, such as GNSS antenna phase center offsets and SLR range biases. In this presentation, we present work carried out by the ESA/ESOC Navigation Support Office on the joint processing of GNSS and SLR at the observation level. Our approach – fittingly referred to as COOL (“COmbination at the Observation Level”) – incorporates the primary geodetic ILRS targets LAGEOS-1, LAGEOS-2, LARES-2, Etalon-1, and Etalon-2, and makes use of space ties provided by the Sentinel and Galileo satellites to directly link the two geodetic techniques. Particular attention is given to the Galileo transmit antenna z-offsets and the numerous SLR range biases, which require careful treatment, as they are known to directly influence the scale of the reference frame solution. The primary motivation for this work is to ensure full readiness for the future ESA GENESIS mission, which aims to establish a highly accurate, next-generation International Terrestrial Reference Frame (ITRF) through the use of all four space geodetic techniques, including DORIS and VLBI, on a single platform and the exploitation of the space ties between them.

How to cite: Dilssner, F., Springer, T., Sermanoukian, I., Otten, M., Gini, F., and Schönemann, E.: Keeping It COOL: GNSS–SLR Combination at the Observation Level, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18349, https://doi.org/10.5194/egusphere-egu26-18349, 2026.

Genesis is an ESA mission conducted by the ESA Navigation Directorate as part of the FutureNAV program. Its primary objective is the contribution to the improvement of the International Terrestrial Reference Frame (ITRF) towards an accuracy of 1mm and a long-term stability of 0.1mm/year. Secondary objectives include the contribution to a high number of other scientific disciplines (geodesy, geodynamics, earth rotation, geophysics, atmosphere and ionosphere sciences, metrology, relativity…) [1].

The Genesis Space Segment consists of a single spacecraft in MEO (400kg, 6000km altitude, 95° inclination) co-locating for the first time in space the four geodetic instruments used for the realisation of the ITRF: a GNSS receiver, an SLR reflector, a VLBI transmitter and a DORIS receiver. The Ground Segment is composed of a Mission Control Centre (including a Ground Station) and will make use of the existing ground infrastructure, operated by the Services of the International Association of Geodesy: GNSS sensor stations network of the IGS, SLR stations of the ILRS, VLBI antennas of the IVS, and DORIS beacons of the IDS. The scientific mission data will be processed, archived, and distributed by ESA Data PROcessing, Archiving and Delivery facility (PROAD), under the responsibility of the Navigation Support Office and the GNSS Science Support Centre, in close collaboration with the scientific community.

Genesis’ fully calibrated satellite will establish precise and stable ties between the key geodetic techniques, implementing a unique dynamic space geodetic observatory. As the ITRF is recognised to be the foundation of countless space and ground-based applications, Genesis will have a major impact on almost any space mission and on Navigation and Earth Science.

On the industrial side, the company OHB Italia has been contracted by ESA as prime for the development, qualification, launch and 2 years operation of the mission (with option for extension), with a launch currently planned in 2028. Antwerp Space, as payload prime, is responsible for the geodetic instruments. Industrial activities were kicked-off in April 2024, the System Requirements Review was successfully closed-out in Q4 2024, the System Preliminary Design Review was successfully carried out in Q4 2025, and work is on-going to consolidate the design towards a Critical Design Review starting in Q4 2026.

On the scientific side, a Genesis Scientific Exploitation Team (GSET) was set-up and members appointed in Q2 2024. This structure encompasses representatives of ESA, a lead Scientific Coordinator and Co-Coordinator, as well as five Working Groups covering the four geodetic techniques and their combination. The GSET includes members of the international geodetic services and will interact with them for the coordination of the ground infrastructure. Two successful Genesis Scientific Workshops were held in February 2024 and April 2025, and a third will be held in March 2026. The GSET has been actively supporting the mission development, the requirements/design consolidation, and will play a key role in the future exploitation of the mission data.

This presentation will provide an up-to-date overview of the Genesis mission from a system, programmatic, and scientific point of view.

[1]: Delva et al. Earth, Planets and Space 75, 5 (2023)

How to cite: Fusco, G., Gidlund, S., Waller, P., Honoré-Livermore, E., Bieringer, A., Schoenemann, E., Berton, J.-C., and Gini, F.: Genesis: A Unique Geodetic Satellite Mission at the Foundation of Navigation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19242, https://doi.org/10.5194/egusphere-egu26-19242, 2026.

The BKG/DGFI-TUM IVS Combination Centre (IVS-CC) officially contributes to the realization of the International Terrestrial Reference Frame (ITRF) by incorporating the contributions from the IVS Analysis Centres (ACs).

For the 2025 update of the ITRF 2020 (ITRF2020-u2025), the IVS initiated a reprocessing of the full VLBI observation history since 1979. Besides S/X-band and VGOS sessions, for the first time, K-band VLBI sessions are included in the ITRF contribution. Moreover, on an empirical basis, the IVS-CC provides combined normal equations that include radio source positions as parameters, allowing for the joint and consistent computation of terrestrial and celestial reference frames, and EOPs as the link between them.

This presentation focuses on developments in the framework of the IVS-CC combination setup for the IVS contribution to ITRF2020-u2025.  A total of 7613 S/X, 219 VGOS, and 229 K-band VLBI sessions will be used for this study. We begin with a description of our combination setup, followed by validation of the input data provided by the contributing ACs and the combined IVS contribution to ITRF2020-u2025. The investigation focuses on the quality of geodetic products estimated by different session types across eclectic frequency bands, including legacy S/X, VGOS, and K-Band.

How to cite: Raut, S., Kehm, A., Bachmann, S., Bloßfeld, M., Seitz, M., Balidakis, K., Klemm, L., Schneider-Leck, S., and Thaller, D.: BKG/DGFI-TUM IVS Combination Centre's advancements within the framework of the IVS Contribution to ITRF2020-u2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20186, https://doi.org/10.5194/egusphere-egu26-20186, 2026.

The International Terrestrial Reference Frame (ITRF) is the foundation for Earth science and operational geodesy applications. It is built on international cooperation over more than three decades for the benefit of countries, regions and global geodesy.  Substantial improvements have been constantly made in the data analysis strategy, at the level of both individual geodetic techniques, as well as the ITRF combination, with the aim to improve the ITRF accuracy and reliability. Motivated by a number of reasons that will be exposed in this paper, the ITRS Center decided to regularly (yearly) update the ITRF2020, with a first update (ITRF2020-u2023) released in December 2024, a second update (ITRF2020-u2024) released in September 2025 and a third update foreseen in 2026. Results of these updates will be presented and discussed, with a special focus on the uncertainty evaluation regarding the stability of the frame physical parameters (origin and scale), as well as Earth Rotation Parameters when adding extended data from the four techniques: VLBI, SLR, GNSS and DORIS. Future plans and perspectives regarding the ITRF2020 updates and consequences for the most demanding user needs conclude the presentation.

How to cite: Altamimi, Z., Rebischung, P., Collilieux, X., Metivier, L., Chanard, K., and de La Serve, M.: ITRF2020 Updates and Future Perspectives, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22667, https://doi.org/10.5194/egusphere-egu26-22667, 2026.

Genesis is an ESA mission in preparation within the Navigation Directorate under the FutureNAV Programme, dedicated to advancing space geodetic science and the International Terrestrial Reference Frame (ITRF). It co-locates GNSS, SLR, DORIS, and a pioneering VLBI transmitter on a single satellite in near-polar orbit (~6000 km), creating a dynamic space geodetic observatory that delivers well-calibrated space ties between all techniques.

These co-located measurements enable rigorous integration of space-geodetic techniques, revealing and mitigating inter-technique biases that currently limit ITRF scale, origin, and orientation. The Genesis objectives demand a stable and well-characterised platform as well as rigorous calibration of instruments and antennas, including phase/group delays and phase center offsets. The mission's novelty and methodology at mm-level demand also the careful preparation of observation strategies and adoption of data analysis and combination techniques for Genesis data exploitation.

Here, we present an overview of the ongoing activities relevant to the science community and ITRF realisation, including the scientific objectives and the status and plans of science instruments and calibrations. The scientific datasets and expected data products, along with their planned availability to the scientific community, will also be discussed.

How to cite: Karatekin, Ö., Vespe, F., Altamimi, Z., Seitz, F., Dach, R., Männel, B., Haas, R., Moreaux, G., courde, C., Bieringer, A., Schoenemann, E., Waller, P., Fusco, G., and Gidlund, S. and the Genesis Science Exploitation Team: Science objectives of ESA's Genesis mission: a flying geodetic observatory to improve ITRF accuracy and stability , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22731, https://doi.org/10.5194/egusphere-egu26-22731, 2026.

Strong-motion acceleration records are crucial for seismic research and vibration analysis. Still, baseline offsets often introduce drift in displacement integration estimates, compromising the accuracy of the coseismic displacement retrieval. By providing precise ground deformation signals, the high-rate Global Navigation Satellite System (GNSS) offers ideal baseline correction constraints. In this paper, we propose a baseline correction method based on acceleration smoothness priors and co-located high-rate GNSS static displacement constraints. First, accelerations are processed using the smoothness priors method (SPM). This method separates steady-state acceleration signals from potential non-periodic noise trends through regularization. Second, static displacements from co-located high-rate GNSS stations are applied as external constraints to refine a step-fitting function. The optimal baseline correction time parameters are iteratively determined through a grid search method. Finally, the displacement time series is then fitted with this constrained step-fitting function to achieve baseline deviation correction of acceleration records. A shake table experiment and two seismic events validated the proposed baseline correction method. In the shake table experiment, the corrected displacement time series returned to the zero line, preserving long-period and permanent displacement information, with a root mean square (RMS) of 0.585 cm and a correlation coefficient (CC) of 0.964. For the 2023 Turkey earthquake doublet, the corrected strong-motion displacements showed good agreement with GNSS data, achieving an average RMS of 2.720 cm and a CC of 0.799. For the 2021 Maduo Mw 7.4 event, the method yielded an RMS of 0.585 cm and a CC of 0.964, with an average RMS of 1.157 cm and a CC of 0.592 in all directions. This demonstrates its potential as a key technique for accurately retrieving source parameters and finite fault slip inversion from strong-motion accelerometer data.

How to cite: Zhang, Y., Li, Y., and Shan, X.: Strong motion baseline correction based on acceleration smoothness priors and co-located GNSS static displacement constraints, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1482, https://doi.org/10.5194/egusphere-egu26-1482, 2026.

The Global Navigation Satellite Systems (GNSSs) have the invaluable ability to monitor the crustal deformation either for geodesy (determination of the shape of the Earth) or for geophysics (interpretation of geodynamical processes). However, these systems have some limitations. Among the others, the systematic errors and unmodelled effects defined and observed as a common mode error (CME) have to be mentioned. Isolation of CME from displacements seems to be crucial for obtaining reliable velocities and their uncertainties. In this research we use a set of European GPS-derived vertical displacements recorded at 4443 permanent stations provided by the Nevada Geodetic Laboratory (NGL) and, in the first step, we compare them with displacements predicted by non-tidal atmospheric (NTAL), hydrospheric (HYDL), oceanic (NTOL), and barystatic sea level (SLEL) loading models provided by the GFZ Helmholtz Centre for Geosciences to obtain a consistent picture of GPS sensitivity to loadings over Europe. This part of the study allowed us to confirm a very high correlation but varied depending on the region of Europe. Then, we divided GPS stations regionally upon the results of noise analysis and the common mode error was determined using the probabilistic Principal Component Analysis (pPCA) method. We note a significant correlation between the NTAL model and the CME values, which indicates that in Europe, most of the CME is driven by the unmodeled atmospheric effect with some regional anomalies. Finally, we provide a discussion on the differences in the values of velocities of GPS permanent stations together with their uncertainties after removing the CME values.

How to cite: Bogusz, J. and Klos, A.: Exploring the common mode error: case study of Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1667, https://doi.org/10.5194/egusphere-egu26-1667, 2026.

Satellite clock offset products are fundamental to high-precision Global Navigation Satellite Systems (GNSS) applications. Clock series derived from L-band Orbit Determination and Time Synchronization (ODTS) method generally exhibit good short-term stability but suffer from pronounced day-boundary discontinuities (DBDs). Furthermore, the orbit modeling errors absorbed into the clock estimates degrade the clock long-term stability. Inter-satellite link (ISL) technology provides an additional source of clock estimated information. Clock offsets derived from geometry-free ISL observables are almost immune to orbit errors and therefore offer better long-term stability. However, the limited ranging precision introduces larger random noise into ISL clocks, leading to the poorer short-term stability. Consequently, combining the above two measurement types is a logical strategy to optimize the overall clock solution. To exploit their complementary characteristics, we apply the Vondrak-Cepek (V-C) filter to combine 31 days of ISL clock offsets with the time derivatives of ODTS clocks provided by Deutsche GeoForschungsZentrum (GFZ). The results demonstrate that the V-C filter effectively suppresses observation noise without distorting the true signals. The combined clock product preserves the continuity of ISL clocks while maintaining the low noise level of the ODTS solution. After quadratic detrending, the combined clock residual is about 0.10 ns, comparable to those of ISL and significantly better than the GFZ value of 0.15 ns. In terms of overlapping Allan deviation, the combined clocks closely follow the GFZ performance at short averaging times and approach or even surpass the ISL stability at long intervals, achieving a balanced compromise between short- and long-term performance. The improvement in stability arises from both the complementary fusion of the two datasets and the smoothing properties of the filter. This study provides a new perspective on GNSS satellite clock combination and a practical method for fully exploiting the strengths of different clock products.

How to cite: Geng, T., Yan, K., Xie, X., and Zhao, Q.: Combination of GNSS satellite clock offsets from L-band ground-tracking and inter-satellite link measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2026, https://doi.org/10.5194/egusphere-egu26-2026, 2026.

How to cite: Qu, X. and Ding, X.: Real-time Rotation Monitoring of Offshore Structures based on GNSS and Accelerometer Data Fusion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2231, https://doi.org/10.5194/egusphere-egu26-2231, 2026.

GNSS precise point positioning (PPP) requires precise satellite orbit, clock and code/phase bias products. The International GNSS Service (IGS) has been operationally providing such high-precision valuables in support of science and society. Since the IGS encompasses various analysis centers (ACs), it is usual practice to compare these solutions to provide feedback to the ACs and also to combine them to generate the official IGS products with higher stability, reliability, completeness, and robustness. Under the current IGS framework, the AC Coordinator (ACC, acc.igs.org) manages orbit and clock combinations, while the Ionosphere Committee (IC, igs.org/wg/ionosphere) and Reference Frame Committee (RFC, igs.org/wg/reference-frame) are responsible for ionosphere products and station coordinates. Meanwhile, the newly established Wuhan Combination Center (WCC, igs.org/wg/wcc) is acting as an experimental alternative to augment the legacy combination procedures.  Usually, a “summary” file containing the combined statistical results is generated to facilitate contributions from ACs. However, such a summary file format shows a few limitations, e.g., failure in complying with a dedicated format standard, no statistics for the combined code/phase bias products and insufficient quality evaluation indices, such as anomalous satellites, outlier clocks, and so on. Consequently, these limitations hinder automated parsing and diminish human interpretability of the summary results. During the 2025 Governing Board meeting in Rimini, the IGS formed a task force led by WCC in collaboration with ACC and the Infrastructure Committee, to define a format standard to address the limitations of the traditional summary file. Specifically, the primary objectives of the task force are threefold: first, to establish a format that enables ACs to easily inspect their products artifacts; second, to establish a format that allows PPP and other users to easily exclude outlier products; and third, to develop auxiliary scripts for plotting the combination statistics. The proposed format is expected to support ACs in troubleshooting and verification of their products, along with downstream users for both network and PPP processing, e.g., by enabling consistent quality screening and exclusion of outlier products.

How to cite: Geng, J., Wen, Q., Wang, B., and Zhang, Y. and the The IGS Task Force to Standardize GNSS Product Combination Statistics: The IGS task force for a standardized format of GNSS satellite product combination statistics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2264, https://doi.org/10.5194/egusphere-egu26-2264, 2026.

How to cite: Kitpracha, C., He, S., Brack, A., and Satirapod, C.: An optimization of the tropospheric correction interpolation method for PPP-RTK technique in Thailand, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4736, https://doi.org/10.5194/egusphere-egu26-4736, 2026.

The zero-difference (ZD) and double difference (DD) approach for processing GNSS observations is mathematically equivalent – meaning that in DD case the huge number of clock parameters are just pre-eliminated. The results for all remaining parameters are identical, if no numerical shortcut is done (e.g., ignoring parts of the correlations introduced by the DD approach). The advantage of processing DD observations is the reduced number of parameters, easier detection and potential correction of cycle slips, and direct access to the integer ambiguities without any phase bias parameter. On the other hand, ZD processing offers greater flexibility in network configuration and parameter handling. This is particularly advantageous when modifying the list of stations in the processing, including Low Earth Orbiting satellites (LEOs), or implementing advanced clock models, e.g., for Galileo satellites.

Based on an experimentally developed ZD-based ambiguity resolution method that introduces ambiguity clusters and satellite-wise consistency corrections, the original research prototype was translated into a robust and automated routine processing chain which is suitable for operational use.

The new procedure follows the structure of the established CODE DD strategy but adapts the individual processing steps, e.g. pre-processing, estimation of global parameters, handling of receiver-dependent parameters, and ambiguity resolution. Special emphasis is placed on numerical stability, the reliable handling of real-valued ambiguities, and the introduction of quality-control mechanisms designed for long-term autonomous operation. The resulting procedure enables efficient parallelization and delivers consistent orbit, clock, and ambiguity products. We have investigated the requirements on the station density for all these steps in order to optimize also the processing time. Stations, that are not needed in this context can get pre-processed based on the PPP approach and get added to the final solution only.

Initial results show that the operational ZD processing chain reaches the accuracy and stability of CODE DD-based products while offering greater flexibility for future extensions. The results demonstrate that the ZD-based GNSS processing is sufficiently mature to generate stable global products on a daily basis and therefore represents a promising foundation for next-generation GNSS solutions computed at CODE.

How to cite: Kobel, C., Rodriguez, E., Dach, R., Arnold, D., Brockmann, E., Kalarus, M., Lasser, M., Schär, S., Stebler, P., and Jäggi, A.: Towards Routine zero-difference GNSS Processing at Center for Orbit Determination in Europe (CODE), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4841, https://doi.org/10.5194/egusphere-egu26-4841, 2026.

In recent decades, Precise Point Positioning (PPP) has become a highly effective Global Navigation Satellite System (GNSS) positioning method and promising alternative to well-established relative positioning techniques. PPP is characterised by the use of precise satellite data (such as satellite orbits, clocks, and biases) and the accurate modelling of various error sources. PPP allows us to achieve position accuracies at the centimetre or even millimetre level. However, its widespread use has been limited due to significant convergence times. Among other approaches, innovative PPP models and PPP with integer ambiguity resolution (PPP-AR) have proven to be the most effective in reducing this time.

The decoupled clock model (DCM) provides an elegant way to perform PPP-AR in an uncombined approach for any number of frequencies. The idea is to estimate separate receiver clock errors for code and phase observations, resulting in a receiver code clock error and a receiver phase clock error. Additionally, the unknowns are reparametrized in such a way that the integer property of the phase ambiguities is conserved, with a datum satellite being used to set the phase ambiguities' datum. Unlike other PPP-AR approaches, direct differencing with a reference satellite is not necessary. PPP-AR can therefore be performed in a straightforward manner.

In this contribution, we discuss the DCM and its key characteristics. We present PPP results achieved with the uncombined DCM and GPS, GLONASS, Galileo, and BeiDou observations on three frequencies at thirty-second and one-second intervals. We then evaluate convergence behaviour, coordinate accuracy, ZTD estimation, and ambiguity fixing rates. The PPP investigations were conducted using the open-source software raPPPid. Our findings show that instantaneous PPP convergence to centimetre-level accuracy can be achieved within two to three measurement epochs.

How to cite: Wareyka-Glaner, M. F. and Möller, G.: Instantaneous PPP convergence with a Decoupled Clock Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5001, https://doi.org/10.5194/egusphere-egu26-5001, 2026.

Dual-frequency ionosphere-free (IF) combinations, commonly used in real-time low Earth orbit (LEO) kinematic orbit determination, effectively remove ionospheric delay errors but significantly amplify noise in code pseudorange observations, thereby limiting orbit accuracy. To address this limitation and enhance real-time orbit precision, this study investigates a code–carrier smoothing approach integrated into a standard point positioning (SPP)-based kinematic orbit determination (OD) framework.

The Sentinel‑6A satellite’s onboard GNSS code pseudorange observations were processed in real-time mode using least squares estimation (LSE) to estimate the satellite’s position, velocity, and clock offset. Ionospheric effects were mitigated by applying IF combinations derived from GPS (L1/L2) and Galileo (E1/E5) dual-frequency signals. To suppress short-term code noise, a Hatch filter-based code–carrier smoothing technique was implemented, in which noisy code pseudorange measurements were combined with precise carrier-phase measurements to produce stabilized pseudorange observables. A smoothing window constant of 16 epochs was adopted to enable recursive real-time processing.

GNSS observation data in RINEX format and reference SP3 orbit products for the Sentinel‑6A satellite were obtained from the Crustal Dynamics Data Information System (CDDIS) and the European Space Agency (ESA) archives. The dataset consisted of 10-second sampling over a 24-hour period starting at 00:00 UTC on April 20, 2025. Broadcast ephemerides of GPS and Galileo satellites were used for real-time orbit derivation.

The kinematic orbit estimates were evaluated at 10-second intervals using the SP3 orbits as reference truth. Without smoothing, the root-mean-squared errors (RMSEs) were 59.5 cm (radial), 27.9 cm (along-track), and 22.9 cm (cross-track), yielding a 3D RMSE of 69.6 cm. With the Hatch filter applied, the corresponding RMSEs improved to 50.0 cm, 23.1 cm, and 18.1 cm, resulting in a 3D RMSE of 58.0 cm. These results represent improvement rates of 16.0%, 17.2%, 21.0%, and 16.7% in the radial, along-track, cross-track, and 3D directions, respectively.

The findings confirm that Hatch filter-based code–carrier smoothing effectively reduces pseudorange noise and improves the precision of real-time kinematic orbit determination for LEO satellites.

How to cite: Lee, H.-S., Choi, H.-Y., and Park, K.-D.: Real-Time LEO Satellite Kinematic Orbit Determination Using Code-Carrier Smoothing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6051, https://doi.org/10.5194/egusphere-egu26-6051, 2026.

Although tightly coupled Precise Point Positioning/Inertial Navigation Systems (PPP/INS) are capable of decimeter-level accuracy, conventional filtering frameworks suffer from a theoretical disconnect: attitude errors are mapped onto the special orthogonal group SO(3), while position and velocity errors are treated in Euclidean space. This mathematical heterogeneity often induces error accumulation during state propagation. To resolve this, this paper presents a multi-frequency PPP-AR/INS framework based on the Left-Invariant Lie Group. By strictly defining all state errors on the Lie group manifold, estimation consistency is significantly enhanced. Field experiments confirm the superiority of the proposed approach over traditional methods. Specifically, under open-sky conditions, the left-invariant formulation outperforms the right-invariant and conventional method by reducing 3D positioning errors by 3.3% and 9.3%, respectively. In challenging environments with partial signal blockage, the method yields improvements of 4.8% for 2D and 13.1% for 3D. Furthermore, during complete GNSS outages, the enhanced accuracy of the IMU state estimation mitigates drift, lowering 2D and 3D errors by 11.2% and 6.3%, respectively. Notably, these gains are achieved with only a marginal 2.4% increase in computational load, validating the efficiency of the method for real-time applications.

How to cite: Song, H., Tao, G., and Li, Z.: Lie Group model and performance analysis of Triple-Frequency PPP-AR/INS Tightly Coupled Integration, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6061, https://doi.org/10.5194/egusphere-egu26-6061, 2026.

GNSS measurements are recognized as a key technique for ionosphere monitoring. Such a goal is typically realized with datasets from global or regional networks of permanent stations, which provide, e.g., vertical total electron content maps. Despite the unquestioned role of such an approach, it still suffers from an irregular distribution of on-ground monitoring sites, limiting the precision of GNSS-based ionospheric products. A solution addressing this issue is to adopt dual-frequency measurements from low-cost devices, particularly those provided by GNSS chipsets embedded in modern smartphones. These ubiquitous devices can, theoretically, lead to the extreme densification of ionospheric information; however, their widespread use must be preceded by a detailed analysis of data properties and quality.

This still-open issue motivated us to investigate the applicability of ionosphere monitoring using a geometry-free linear combination (GF LC) series built of smartphone-acquired GNSS phase data. In the experiment, we used two smartphones: Google Pixel 7 and Xiaomi 15T Pro, which provide multi-system dual-frequency measurements. The smartphone results were validated against those provided by a high-grade receiver - Trimble Alloy. The dataset comprised GPS, Galileo, and BDS observations collected during three 8-hour sessions. We analysed the completeness and quality of the data, including the noise level, the number of cycle slips, and the consistency and accuracy of smartphone GF LC time series in comparison to the benchmark values. While the analysis confirmed the applicability of smartphone measurements for ionospheric studies, it also revealed the poorer quality of all analysed characteristics. Furthermore, we observe a substantial performance discrepancy between the tested mobile devices, which may pose a problem for their combined utilization.  

How to cite: Sieradzki, R., Paziewski, J., Szczepanik, H., Geng, J., and Li, G.: On the feasibility of ionospheric sounding with modern dual-frequency smartphones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6481, https://doi.org/10.5194/egusphere-egu26-6481, 2026.

High-quality GNSS receivers and strong-motion accelerometers provide reliable and conventional data, now commonly used in early warning systems for geohazards, seismology, and civil engineering applications. Although their capability to deliver precise measurements has been established, their overall monitoring effectiveness can be constrained by the insufficient spatial coverage and densification of these sensors. Conversely, we are now in an era where mass-produced, affordable GNSS and MEMS sensors are widely available, and recent research indicates that they can offer precise GNSS and accelerometer observations. Particular attention is given to sensors embedded in modern smartphones. These widely used, but unprofessional sensors could potentially serve as detectors and providers of rapid, spatially dense information on dynamic movements. In this study, we explore and validate the applicability of precise dynamic displacement detection using GNSS observations and accelerometer data from sensors embedded in selected recent smartphones, such as Xiaomi 14. The validation was performed by means of retrieving artificial vibrations and dynamic motions, which were induced by the Quanser I-40 shake table. With the proposed combined GNSS and accelerometer solution based on smartphone data, we demonstrate the feasibility of precisely detecting sub-centimeter dynamic displacements. The results of the proposed approach based on smartphone data show that smartphones may soon be considered an auxiliary instrument in seismic and structural health monitoring applications.

How to cite: Paziewski, J., Sieradzki, R., and Szczepanik, H.: On the path to dynamic displacement detection with smartphone GNSS and accelerometer data , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6652, https://doi.org/10.5194/egusphere-egu26-6652, 2026.

Multipath noise, a site-specific error influenced by the surrounding environment of Global Navigation Satellite System (GNSS) antennas, continues to be a significant challenge in kinematic GNSS positioning, particularly for detecting subtle crustal deformations over hours to days. While the sidereal filter is widely used for its simplicity, it is not always well-suited for multi-GNSS data. The Multipath Hemispherical Map (MHM) method offers better performance and multi-GNSS compatibility. Still, it is often implemented in a software-dependent manner, and isolating multipath from other errors, such as tropospheric delays, is difficult. To overcome these issues, we propose the Multi-Site Stacked MHM (MSS-MHM) method, which builds a hemispherical map by stacking carrier-phase residuals from multiple short-baseline relative positioning solutions. In this setup, residuals that substantially reduce common-mode tropospheric, ionospheric, and clock errors are mapped onto a satellite azimuth-elevation grid. This map is then used to correct the original Receiver Independent Exchange Format (RINEX) observation file, thereby enabling use with a wide range of software. Applying MSS-MHM to 30-second long-baseline kinematic analyses with multi-GNSS data showed that increasing both the number of baselines and stacking days significantly reduced coordinate time series noise. Power spectral density analysis indicated that noise reduction was most effective for periods longer than ~1,000 seconds. Moreover, using the corrected RINEX file across four different positioning software packages (Double-Difference and Precise Point Positioning strategies) improved coordinate stability in our tests. These results highlight MSS-MHM as a software-agnostic, observation-level correction framework for multipath mitigation, applicable across the strategies and software evaluated here.

Acknowledgments: The SoftBank's GNSS observation data used in this study was provided by SoftBank Corp. and ALES Corp. through the framework of the "Consortium to utilize the SoftBank original reference sites for Earth and Space Science."

How to cite: Ito, Y. and Ohta, Y.: Observation-Domain Multipath Mitigation in Global Navigation Satellite System Positioning Using Multi-Baseline Stacked Carrier-Phase Residuals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6782, https://doi.org/10.5194/egusphere-egu26-6782, 2026.

Precise Point Positioning (PPP) is widely used in high-precision GNSS applications, and its performance depends primarily on the orbit and clock products provided by the International GNSS Service (IGS). This study evaluates the impact of using products derived from different IGS Analysis Centers (ACs) on PPP solution quality, using data collected during a GNSS campaign conducted to study an active fault in Oran, Algeria. Data from multiple GNSS stations, located in both open-sky and challenging/constrained environments, were processed using static and kinematic PPP modes with various IGS ACs products. As long-duration observations showed no significant differences, only 30-minute sessions were processed to provide a clear evaluation of solution quality. Position uncertainties, carrier-phase residuals, and kinematic position repeatabilities were analyzed to assess the quality of the solutions. To ensure a fair comparison between the ACs’ products, the analysis was limited to products with the same number of observed satellites and a consistent 30-second clock rate. Furthermore, to include the maximum number of ACs, both OPS and MGEX products were considered, and only GPS and GLONASS satellites were used, as these are provided by the majority of IGS ACs.

Our analysis of epoch-wise phase residuals across multiple IGS ACs, indicates that the residual behavior is remarkably consistent across stations. Exceptions occur at more challenging stations, where some ACs’ solutions, such as GRG, exhibit slightly lower residuals quality. Similarly, for solution repeatability, most ACs products provide comparable results, with GRG again performing slightly worse, particularly in the vertical component showing an RMS repeatability of approximately 30 mm compared to 23 mm at the challenging station AGF21. In terms of positional uncertainties, all solutions demonstrate good horizontal and vertical precision, with values ranging from 1 to 4 mm. Among the ACs, COD (MGX), GFZ, and GRG show marginally better horizontal performance, while JGX performs slightly worse in both components. Vertical uncertainties benefit as well, with improvements of about 4 to 6 mm observed when using COD (MGX), GFZ, and GRG products, especially at the more challenging stations.

How to cite: Bouaoula, W. and Hasni, K.: Impact of using products from different IGS analysis centers on PPP solution quality : A GNSS campaign in Oran, Algeria, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7171, https://doi.org/10.5194/egusphere-egu26-7171, 2026.

Seasonal variations in GNSS coordinate time series are largely driven by environmental mass loadings, which involve not only instantaneous elastic deformation but also time-dependent poroelastic and hydrological responses. Assuming an instantaneous Earth response may bias long-term deformation estimates and affect reference frame stability. We select 4,711 global vertical GNSS coordinate time series spanning at least a decade with > 95% data completeness, together with their corresponding environmental loading deformation time series, both provided by the Nevada Geodetic Laboratory. To address the combined effects of multiple environmental loads, we first identify the dominant loading component at each station — defined as the one contributing more than 75% of the total modeled seasonal deformation amplitude. Then we extract annual signals from both GNSS and the dominant loading deformation time series using Singular Spectrum Analysis and estimate the phase lags between them through cross-correlation algorithm. This approach minimizes interference from secondary loading sources and provides a clean estimate of the time lag associated with the primary driving process. Globally, hydrological loading induces phase delays with significant spatial variability (standard deviation: 41 days). These phase lags exhibit systematic spatial patterns, possibly reflecting diverse hydrological processes across regions: negative delays (GNSS lagging load by ~ 28 days) in the mountainous western United States are possibly associated with unmodeled deep subsurface water retention; widespread positive delays (GNSS leading load by ~ 13 days) in the U.S. Corn Belt and Europe suggest rapid water removal due to human activity; and anti-phase anomalies (difference of > 150 days) in confined aquifers may reflect poroelastic responses. Applying the phase-lag correction by subtracting the time-shifted annual loading signals from GNSS observations improves the consistency between them at ~ 70% of the stations compared to the standard instantaneous correction, with a median reduction in annual signal power increasing from 40.4% to 62.1% (69.2% to 85.2% in regions with strong hydrological loading like the Amazon and the mountainous western U.S.) and a concurrent increase in the median weighted root-mean-square (WRMS) reduction from 2.7% to 4.0% (7.2% to 9.7% in the aforementioned regions). It also mitigates potential bias in site-specific velocity estimates (up to 0.04 mm/yr). Our results demonstrate that accounting for phase lags between GNSS observations and loading models is important for refining loading corrections and thereby enhancing the stability of geodetic reference frames.

How to cite: Li, B., Zhou, X., Yang, Y., and Chen, Q.: Global Phase Lags between GNSS and Modeled Hydrological Loading: Implications for Hydrogeophysical Responses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7504, https://doi.org/10.5194/egusphere-egu26-7504, 2026.

Railway reference stations are characterized by long span, strip distribution, cross-regional service, weak graphical structure, and requiring high monitoring precision. In view of this, the traditional modeling approaches for reference uniformity have become no longer quite applicable. Currently, coordinates reference maintenance is conducted separately in each area, so that there exist differences among various reference stations in respect of data processing software, mathematical physical model, solution strategy, adjustment method, and revision cycle. This causes systematic deviation in satellite navigation and positioning service reference between different areas. To ensure the uniformity and timeliness of high-precision location-based service reference of national railways, this study is intended to simulate cross-region, strip, isoheight-shape and Y-shape layout modes based on the actual situation of railway observation network, and implement selection of reference station control points, networking solution scheme design and result analysis considering the reference uniformity solution requirements of different layout modes to propose an inclusive coordinates reference uniformity solution scheme applicable for various strip layout modes and provide a practicable reference for the coordinates reference uniformity solution of reference stations of railways and shipping lanes. This is significant to the coordinates uniformity and regular updating maintenance of high-precision service datum network of railways.

How to cite: Wang, X., Wu, J., Zhang, P., and Liu, C.: Research on the Method for Realizing Datum Uniformity of Cross-region Reference Stations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8611, https://doi.org/10.5194/egusphere-egu26-8611, 2026.

Accurate modeling of the horizontal and vertical variation of the tropospheric horizontal gradient is crucial for correcting space-geodetic tropospheric delays and retrieving atmospheric water vapor. To date, the horizontal variation in the gradient has been well represented by the operational grid-wise products, such as grid-wise GRAD. However, for vertical variation, the relative methods and models are unavailable, which limits the accuracy of the grid-wise products by ignoring the vertical variation from grid height to target height. In this contribution, we analyze the variation characteristics of the asymmetric delay and the horizontal gradient using ERA5 data and the ray-tracing technique, and confirm their significant reductions with height. Then, we introduce a new height-correction method that adjusts for vertical variation in the horizontal gradient based on its characteristic behavior, and the results demonstrate that accounting for height variation can significantly reduce residuals in horizontal gradient modeling. Finally, we developed a global model using this method and validated it against the grid-wise GRAD products, with the site-wise GRAD products as the reference. The results demonstrate that the height-correction model can significantly improve the accuracy of grid-wise GRAD at high-altitude locations, making it suitable for high-altitude stations and unmanned aerial vehicle applications.

How to cite: Zhou, Y., Lou, Y., Zhang, W., and Li, X.: Vertical variation modeling of the tropospheric horizontal gradient, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8623, https://doi.org/10.5194/egusphere-egu26-8623, 2026.

The thermoelastic deformation of GNSS monuments and foundations is a significant contributor to the vertical nonlinear variations observed in the GNSS coordinate time series. A rigorous thermoelastic effect model, which takes into account the diversity of monument depths and foundation types of the reference stations, was proposed in this paper to quantify the influence of thermal expansion on the vertical displacement using 409 GNSS reference stations in Mainland China. The periodic characteristics of the GNSS vertical time series, GREL time series, and thermal expansion effect show a higher consistency between the GREL time series and the thermal expansion effects. The annual amplitude of thermal expansion for GNSS reference stations across Mainland China ranges from 0.2 mm to 1.9 mm, increasing with latitude, with a characteristic distribution of lower values in the south and higher in the north. After applying thermal expansion corrections, 79.2% of the reference stations across Mainland China exhibit a decreasing trend in amplitude, with an average reduction of 0.4 mm. Regional variability in the correction effects is significant: the largest corrections occur in Central China, followed by Northwest China and East China, while corrections in Southwest China, South China, and North China are comparatively smaller, and the corrections in Northeast China are negative. The thermal expansion correction demonstrates similar effectiveness across different types of foundational reference stations. A reduction in amplitude was observed in 78.5% of bedrock monument stations and 80.2% of soil monument stations, with a difference of 1.7% between the two. The average reduction in amplitude variation for different types was the same at 0.4 mm, indicating a comparable effect. Notably, the correction effect varies significantly based on the burial depth of the GNSS monuments, with the largest correction observed for the 5.5 m soil monument stations, followed by 2 m bedrock monument stations, 18 m soil monument stations, and 7.5 m soil monument stations. The correction effect for 8.5 m soil monument stations is negative.

How to cite: Wu, J., Li, Z., Wang, X., Zhang, Y., and Liu, C.: The Impact of Thermal Expansion on Nonlinear Vertical Variations of GNSS Reference Stations in Mainland China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8958, https://doi.org/10.5194/egusphere-egu26-8958, 2026.

Significant spatial heterogeneity of tropospheric water vapor over the Tibetan Plateau, particularly along the vertical dimension, presents a major challenge to traditional tropospheric wet delay models used in GNSS applications across large height ranges. To address this issue, we developed a refined Tibetan zenith wet delay (ZWD) model based on pressure-level ERA5 reanalysis data with a spatial resolution of 0.25°, providing ZWD estimates at arbitrary times and heights. The model adopts an improved vertical correction in which ZWD vertical profiles are represented by a cubic polynomial height-correction function. The polynomial coefficients are estimated at each ERA5 grid node using ERA5-derived ZWD profiles and are further parameterized using harmonics up to the semidiurnal term to characterize temporal variability. ZWD at user locations is obtained through bilinear interpolation of the four surrounding grid nodes, ensuring continuous spatial and vertical coverage over Tibet. Validation using ERA5- and radiosonde-derived ZWDs shows that the TZ model achieves lower bias and reduced root-mean-square error (RMSE) than the widely used GPT3 model at both surface and elevated layers. These results indicate stable performance of the model across the full altitude range. The proposed model can be readily integrated into GNSS positioning frameworks. In precise point positioning (PPP), it may be introduced as a virtual observation of ZWD, with the model RMSE used to define the initial measurement-noise covariance. As the model provides a priori information rather than true observations, a time-varying down-weighting strategy is applied so that the ZWD estimation progressively relies on actual GNSS observations. In network real-time kinematic (NRTK) applications with large height differences, model-derived ZWD combined with mapping functions can be used to mitigate height-dependent double-differenced tropospheric delay residuals. This improves positioning accuracy, especially in the vertical component.

How to cite: Liu, C., Wu, J., Wang, X., and Xu, C.: A refined tropospheric zenith wet delay model for GNSS applications over the Tibetan Plateau, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9198, https://doi.org/10.5194/egusphere-egu26-9198, 2026.

All geodetic space techniques used today are based on measuring the propagation time of electromagnetic waves between a transmitter and a receiver. The atmosphere is one of the most limiting factors for the achievable accuracy of the observation techniques. The wet part of the troposphere, particularly water vapour, has a strong and highly variable influence on signals in the microwave range, as is the case with GNSS. By using current models, this high variability makes it difficult to sufficiently correct the influence of the troposphere on the signal propagation time. Neither weather models nor estimation of parameters can accurately capture the high tropospheric variability. An alternative method for determining the wet propagation delay is a water vapour radiometer.
With the HATPRO-G5, the Geodetic Observatory Wettzell has a modern radiometer that is capable of measuring the wet part of the troposphere above the station not only at the zenith but also for various azimuth-elevation combinations. This allows the wet delay to be recorded as a function of azimuth, elevation, and time. The resulting data set will first be analyzed and then used in combination with GNSS observations. To make this data available for GNSS evaluation, the water vapour radiometer data must be smoothed and interpolated both spatially and temporally. To assess the impact of radiometer-based tropospheric correction, the estimated station height component is compared with a standard GNSS processing and with the height component of a station coordinate product. We performed a PPP to estimate the station coordinates. However, the results do not show a clear picture. On the one hand, the estimation of the station height component using radiometer-based correction appears to deliver better results than the classic approach for certain time periods. On the other hand, however, these improvements cannot be reproduced for the entire time period of the data set. The data set still exhibits systematic errors whose origin has not yet been clarified, which in turn negatively affect the accuracy of the height component estimate. Possible reasons for this could include rapid weather changes, rain events or also electronic-specific systematics. Nevertheless, radiometer-based corrections have the potential to positively influence the accuracy of parameter estimation in GNSS processing.

How to cite: Vollmair, P., Schlicht, A., Klügel, T., and Hugentobler, U.: Integration of radiometer data to improve tropospheric correction in GNSS-PPP processing., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9479, https://doi.org/10.5194/egusphere-egu26-9479, 2026.

The positioning accuracy of smartphone-based Global Navigation Satellite Systems (GNSS) is significantly degraded by ionospheric delay. Current correction methods primarily rely on broadcast ionospheric models, which offer limited precision. High-precision real-time ionospheric grid products, while more accurate, require a stable internet connection and incur additional costs, posing a significant constraint for mobile applications in network-free environments. To address this challenge, we propose ST-VIT-NET, a novel deep learning model based on the Vision Transformer (ViT) architecture for real-time ionospheric prediction and correction. ST-VIT-NET learns the deviation between the Klobuchar broadcast model and the high-precision final ionospheric grid product IGS-GIM, thereby enabling high-accuracy ionospheric correction for broadcast ephemeris-based models.

Experimental results demonstrate that, on a global scale, the ST-VIT-NET model achieved an average Root Mean Square (RMS) error of 4.37 TECU in predicting the Vertical Total Electron Content (VTEC) over a 131-day period from day of year 161 to 292 in 2025. This represents reductions of 64.44% and 9.34% compared to the Klobuchar model (12.29 TECU) and the IGS real-time GIM model (4.82 TECU), respectively, indicating strong temporal and spatial generalizability. In static positioning tests, Standard Point Positioning (SPP) using the ST-VIT-NET model with a Huawei P40 smartphone yielded horizontal and vertical RMS positioning errors of 1.35 m and 2.18 m. These values are 52.42% and 62.77% lower than those obtained using the Klobuchar model (2.85 m horizontal, 5.86 m vertical), and 25.42% and 13.71% lower than those using the IGS real-time GIM model (1.82 m horizontal, 2.53 m vertical). In kinematic vehicle tests, SPP using the ST-VIT-NET model with a Huawei Mate40 smartphone resulted in horizontal and vertical RMS errors of 2.37 m and 3.81 m. This corresponds to reductions of 59.62% and 62.51% compared to the Klobuchar model (5.87 m horizontal, 10.16 m vertical), and 13.41% and 33.01% compared to the IGS real-time GIM model (2.74 m horizontal, 5.69 m vertical).

Collectively, the findings confirm two key contributions of the proposed model. First, ST-VIT-NET demonstrates strong temporal and spatial generalizability, as evidenced by its sustained high-precision VTEC prediction capability over an extended 131-day period across diverse regions. Second, it provides a viable and self-contained solution for achieving real-time high-precision GNSS positioning on smartphones in network-free scenarios, as it delivers accurate ionospheric corrections using only onboard GNSS observations without any external data dependency.

How to cite: Li, G., Geng, J., Lu, J., and Sieradzki, R.: Enhancing Smartphone GNSS Positioning through Deep Learning-Based Ionospheric Prediction and Correction, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11417, https://doi.org/10.5194/egusphere-egu26-11417, 2026.

Within the TRANSFORM² project, seismic events have been simulated on a triaxial earthquake shake table (ANCO R-303) during a series of ten experiments conducted at the Seismological Observatory in Timișoara, Romania, in October 2025. These experiments included 223 variants of motion, consisting of either fully synthetic or natural records of earthquakes occurring in Poland (2019 mining induced seismicity), Italy (2016 Norcia seismic event), Romania (Vrancea 1986 earthquake) and Greece (2020 Samos and 2021 Damasi earthquakes). The tabletop was instrumented with GNSS receivers, including both low-cost and geodetic-grade – some of which were connected to external atomic clocks, accelerometers of both low-cost and professional types, and inclinometers, providing high-resolution, multi-sensor observations. Multiple configurations of the equipment setup, instrument settings, and data processing options.

We introduce a fully documented and organized dataset that will be shared publicly on Zenodo. This presentation discusses an experimental setup, sensor calibration, and integration workflow to combine multi-sensor measurements into one coherent dataset. Several illustrative analyses are included: the comparisons of low-cost versus high-grade GNSS and accelerometer data; preliminary processing results assessment, and visualizations of induced motions across various motion variants.

The provided dataset will enable the geoscience community to validate algorithms for high-frequency GNSS data, accelerometric data, and fusion algorithms, but also related to seismological modeling, ranging from controlled robotic experiments to real-world seismological data.

Acknowledgments: TRANSFORM² is funded by the European Union under project number 101188365 within the HORIZON-INFRA-2024-DEV-01-01 call.

How to cite: Kudłacik, I., Kapłon, J., Nastase, I. E., Tiganescu, A., Elias, P., Kaczmarek, A., Katakonstantis, A., Nistor, S., Galvi, S., Fabris, P., Zuliani, D., and Marmureanu, A.: High-Rate GNSS and Multi-Sensor Benchmark Dataset from Earthquake Simulation Experiments driven by EPOS NFO Community (TRANSFORM²), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12065, https://doi.org/10.5194/egusphere-egu26-12065, 2026.

The Greenland GNSS Network (GNET) consists of 71 geodetic-grade Global Navigation Satellite Systems
(GNSS) stations mounted directly in stable bedrock along the perimeter of the Greenland Ice Sheet
(GRLS). The first continuously running GNSS (cGNSS) station pre-GNET, was set up in 1995 and has
been operating continuously since then. During the fourth International Polar Year (IPY, 2007–2008),
GNET was established with the addition of 49 remote stations, with additional sites added during the
following years. Over time, the installations have undergone various updates, which have helped to
stabilize and improve observations from the network. Early GPS-only receivers have gradually been
replaced by multi-constellation systems, improving positioning precision. The continuous updates have
resulted in a yearly mean of received observations to be above 95% since around 2020 across the network.
Operating cGNSS stations in the remote high Arctic is challenging and can give rise to downtime for
stations in the network. In this project, we aim to publish the most comprehensive, fully processed
positional time-series from GNET up to date, provided as geodetic coordinates and in a local East,
North, Up (ENU) frame, together with metadata documenting station history and development. The
processing is performed using the Precise Point Positioning (PPP) methodology implemented in the
GipsyX 2.5 software [Bertiger et al., 2020].
To evaluate the quality and performance of the processed time series, two analyses are performed. First,
a long-term stability analysis is carried out by fitting and removing a seasonal trajectory model from each
ENU component individually. The residuals are then used to estimate power-law noise characteristics,
derived from Lomb–Scargle periodograms. The analysis shows that all stations in the network can be
expected to operate with a noise profile in the flicker-noise region, −1 < κ < 1. [Goudarzi et al., 2015]
Second, we compare our processed positional time series with two previously published products from
other processing centers: the Jet Propulsion Laboratory (JPL) [NASA Jet Propulsion Laboratory, 2018]
and the Nevada Geodetic Laboratory (NGL) [Blewitt et al., 2018]. The comparison, based on 39 of 71
stations, uses inter-metric correlation analysis of trajectory model parameters fitted to individual time
series. The results show good agreement among the three products in the vertical direction but poor
correlation in horizontal displacements. The JPL and NGL products exhibit a small, non-zero seasonal
signal in the horizontal components, which is not expected [White et al., 2022; Bian et al., 2023; Materna
et al., 2021]. The amplitudes of these signals, however, are very small, suggesting that these signals likely
originate from specific modeling and processing choices during the PPP processing. Consequently, while
the vertical seasonal signals can be interpreted confidently, horizontal seasonal amplitudes and phases
should be treated with caution when using time-series from NGL or JPL compared to the product we
publish.
Overall, the results highlight the importance of processing strategy, noise characterization, and validation
for high-precision GNSS time series in geoscience applications. 

How to cite: Solgaard, C., Winther-Dahl, M., Nylen, T. H., Madsen, F. B., Bjerregaard, O., Longfors Berg, D., Knudsen, P., and Abbas Khan, S.: The Greenland GNSS Network (GNET): Long-Term Stability and Validation of Geodetic-Grade GNSS Measurements of Greenland’s 3D Bedrock Displacement from 1995–2025 , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12342, https://doi.org/10.5194/egusphere-egu26-12342, 2026.

Signal distortion bias (SDB) is a systematic pseudorange bias associated with receiver types. Its presence reduces the consistency of GNSS clock and signal bias estimated from inhomogeneous networks, significantly decreasing the ambiguity resolution rate and negatively affecting positioning and timing performance. Current research does not provide a comprehensive understanding of the error characteristics of SDB, and traditional SDB calibration methods exhibit certain limitations.

This paper first identifies the correlation between SDB and factors such as receiver brand, model, as well as the dependencies on firmware versions, antennas, and radomes. In addition, we propose a geometry-free (GF)-aided multi-GNSS all-frequency SDB calibration method and strategy. The GF assistance addresses the ±0.5 cycle limitation associated with wide-lane (WL) ambiguity rounding, further improving the precision of SDB calibration. Based on this method and MGEX data, we calibrated and analyzed the SDB for all-frequency signals of GPS, Galileo, and BDS-3. Ultimately, we provide SDB corrections for all satellites per receiver group in SINEX BIAS format.

We further investigated the impact of SDB on satellite clocks, code biases, phase biases, and PPP-AR both theoretically and experimentally. Results show that SDB correction significantly enhance the consistency of satellite clock and bias estimates across networks, with BDS-3 improving by over 90% and wide-lane ambiguity fixing rates for different receivers increasing by up to 20% at most. Moreover, an analysis of one-month data from 132 MGEX stations with hourly reset indicates that SDB correction reduces the multi-GNSS kinematic PPP convergence times for Septentrio, Leica, Javad, and Trimble receivers by an average of 0.43, 2.74, 2.63, and 4.28 epochs, respectively, with corresponding PPP-AR convergence improvements of 1.9%, 8.5%, 14.7%, and 17.7%. The average convergence performance across stations with different receiver types improved by 2.4%, 12.1%, 31.3%, and 25.2%, with maximum improvements of up to 70.8%. These analyses fully demonstrate the necessity of SDB modeling and correction, and it is recommended that the IGS Analysis Center adopt it.

How to cite: Xu, S., Guo, J., Li, J., and Zhao, Q.: Multi-GNSS all-frequency SDB calibration and its impact on high-precision products and positioning, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15669, https://doi.org/10.5194/egusphere-egu26-15669, 2026.

Errors and anomalies in real-time State Space Representation (SSR) products can substantially degrade the performance of precise point positioning with ambiguity resolution (PPP-AR). The existing network-based monitoring approaches mainly rely on phase residuals to detect SSR product errors. These methods perform effectively when monitoring stations achieve integer ambiguity resolution, as product errors are then fully expressed in phase residuals. However, for SSR products with ambiguities not fixed, a portion of the product error is absorbed in the float ambiguity estimates while only the remainder manifests in phase residuals. This incomplete error representation prevents reliable assessment, typically leading to the exclusion of these SSR products from service. Such exclusion reduces SSR product availability and can compromise PPP-AR performance in challenging scenarios, where maintaining service continuity is critical. To overcome this issue, this study presents a monitoring and correction framework applicable to SSR products regardless of their ability to support ambiguity resolution. The approach recognizes that product errors in float PPP processing separate into two quantifiable components. The first component is absorbed by float ambiguity parameters and revealed through deviations between estimated ambiguities and their integer values. The second component persists in phase residuals. Extracting and jointly considering both components enables complete error characterization independent of whether ambiguities can be subsequently fixed. The method operates through coordinated processing at multiple monitoring stations. First, the float PPP solutions yield ambiguity deviations and phase residuals for each tracked satellite. These ambiguity deviations exhibit spatial correlation across the monitoring network. Then, wide-area modeling exploits this correlation to estimate systematic and spatially coherent error corrections in the SSR products. The resulting corrections mitigate these error components, after which phase residuals predominantly represent random, uncorrectable errors suitable for anomaly detection and quality evaluation. The experimental validation using real-time SSR products provided by the Centre National d’Études Spatiales (CNES) and wide-area monitoring stations in China demonstrates that the proposed method effectively improves the reliability and availability of SSR products, while significantly enhancing ambiguity resolution robustness and positioning performance in real-time PPP-AR applications.  Compared with phase observation residual-based and no-monitoring methods, the proposed method reduces incorrect ambiguity fixing rates by 0.47% and 4.22%, and three-dimensional positioning errors by 71.7% and 82.2%, respectively.

How to cite: Tian, Y., Shu, B., Zheng, Y., González-Casado, G., Gao, Y., Wang, L., and Rovira-Garcia, A.: Monitoring and correction of SSR product errors using PPP float ambiguity deviations and phase residuals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15869, https://doi.org/10.5194/egusphere-egu26-15869, 2026.

The increasing demand for Earth science applications presents challenges in enhancing geodetic reference frames. Systematic errors currently restrict the accuracy of these frames, as traditional geometric connections between various space-geodetic techniques are inadequate. To tackle this issue, the DFG-sponsored project FOR5456 aims to reduce systematic errors by utilizing clock ties, including the integration of optical clocks into Space Geodesy.

Recent developments in optical clocks have achieved frequency instabilities below 1×10⁻¹⁵ at 1 s integration time. While this level of short-term stability is beyond the immediate needs of space-geodetic instruments, optical clocks offer substantial benefits for the long-term stability of timing signals.

In particular, the long-term coherence of GNSS time transfer can be improved by calibrating receiver-induced phase instabilities. GNSS carrier-phase measurements do not directly represent the phase of the input clock signal, as they are affected by variable delays inside the receiver. This calibration is enabled by an optical delay-stabilized timing system developed at the Geodetic Observatory Wettzell, which provides a highly stable and well-defined phase reference. Based on this infrastructure, we have developed a real-time GNSS phase calibrator that generates a pilot signal synchronized with the phase of the input clock. This pilot signal is then used terrestrially to remove receiver-induced phase instabilities.

GNSS is currently the only continuously operating space-geodetic system capable of continuous comparison of clocks at the 10⁻¹⁸ level and beyond. However, achieving this requires careful mitigation of receiver instabilities is essential. This contribution presents the design of the GNSS phase calibrator, its synchronization procedure with the clock signal, and an analysis of its performance in terms of long-term time and phase stability, enabling future high-precision clock comparisons over extended time scales.

How to cite: Kodet, J., Kimer, M., Wang, Z., and Pany, T.: Towards Clock Ties in GNSS: A Real-Time Phase Calibrator for Receiver Instability Mitigation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16284, https://doi.org/10.5194/egusphere-egu26-16284, 2026.

Noise characteristics of GPS time series have been documented well so far. Nowadays, researchers study the behavior of the noise from GNSS time series. The examples are yet so few in which the spectral behavior of the noise and differences from the GPS solutions are assessed. For this aim, we are testing our in-house time-series analysis software using GPS solutions from the JPL’s GPS time-series archive. The software is being developed in Yildiz Technical University. GNSS data, which is obtained form the IGS’s MGEX experiment, have been processed using PRIDE GNSS software developed by Wuhan University. About 50 globally well scattered MGEX GNSS stations which are capable of acquiring data from 2-5 different GNSS techniques have been selected. Robust estimators are used to remove outliers and data gaps are filled with AR(1). We do not use large matrix computations while estimating the spectral index, learning lessons from the predecessors of the area, rather an iterative and computationally efficient algorithm is used. Alternative algorithms to automatically fix the offsets which are problematic in trend and velocity uncertainty estimation are also offered during the analysis. We calibrate our velocity estimations with those of the GNSS time-series solutions produced by the JPL using GIPSY-X. Initial results seem to be promising. With the contribution of various GNSS techniques (e.g. GALILEO, GLONASS, GPS, BeiDou, etc.) to the geodetic time series analysis the value of the spectral indice changes and the magnitude of the velocity uncertainty on the average becomes smaller. Namely, the noise shrinks and becomes whiter. The velocity uncertainty is reduced by about 11% for the East and 13% for the Up components while the north component stays neutral.

How to cite: Sanli, D. U., Cetin, D., and Erçoban, M.: Change in spectral index and improvement in velocity uncertainty due to MULTI-GNSS contribution to geodetic site velocity estimation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17422, https://doi.org/10.5194/egusphere-egu26-17422, 2026.

As interest grows in leveraging Low Earth Orbit (LEO) satellites in positioning, navigation, and timing (PNT), characterizing ranging errors for LEO satellite signals has become essential for the system design. The ionospheric group delay affecting PNT signals, which causes significant positioning errors, is proportional to the total electron content (TEC) along the signal path. Existing Global Navigation Satellite System (GNSS) ionospheric models (e.g., Klobuchar, NeQuick) provide ionospheric corrections by using broadcast model parameters, enabling real-time estimation of slant TEC (STEC). However, conventional GNSS ionospheric models were primarily developed and validated for the full slant path to GNSS satellites. Thus, they are not directly appliable to LEO satellites, which operate at much lower altitudes than GNSS constellations.  

Accurate TEC estimation for LEO PNT requires precise vertical electron density profiles to account specifically for the ionosphere below the LEO satellite. The NeQuick-G model, developed for Galileo single-frequency users, provides a three-dimensional electron density distribution based on ionospheric parameters of CCIR (International Radio Consultative Committee) numerical map and broadcast effective ionization level (Az) parameters. Several studies have investigated the validity of the NeQuick-G model in estimating partial TEC above LEO satellites (topside ionosphere) for spaceborne applications. Montenbruck & Rodriguez (2020) evaluated its performance for LEO satellite onboard orbit determination using GNSS measurements from Swarm LEO satellites orbiting at mean altitudes of 480 km and 520 km. Oezmaden et al. (2025) extended this analysis to multiple LEO constellations across different altitudes and developed a residual error model for the NeQuick-G model in the topside ionosphere. However, for LEO PNT applications, the NeQuick-G model should be validated for the bottomside ionosphere below the LEO satellite. This study analyzes the residual error of the NeQuick-G model for bottomside STEC by differencing STEC observations from ground receivers and LEO satellite onboard receivers. The bottomside STEC can be estimated by differencing these observations when the ground receiver, LEO satellite, and GNSS satellite are geometrically aligned. Using position data from IGS stations, GNSS, and Swarm satellites, we searched for alignment events for 2019 and 2024 and derived the bottomside STEC. These bottomside STECs are then compared with NeQuick-G model estimates using Az parameters broadcast in Galileo navigation messages.

Residual errors are analyzed under different ionospheric conditions such as solar activity, geomagnetic latitude, and local time. The standard deviations of the residual errors are 10.62 TECU during the solar maximum (2024) and 4.47 TECU during the solar minimum (2019), satisfying Galileo target specification for residual STEC errors (68% probability within 20 TECU or 30% of STEC). The variability of residual error is consistently higher in low latitude regions than at mid or high latitudes, indicating increased model uncertainty associated with equatorial ionospheric dynamics. These findings provide empirical validation of the NeQuick-G model for bottomside ionospheric correction in emerging LEO PNT applications.

References

Montenbruck,O., González Rodríguez,B.(2020).NeQuick-G performance assessment for space applications. GPS Solut 24, 13 https://doi.org/10.1007/s10291-019-0931-2

C.Oezmaden, S.Pelzer, O.G.Crespillo, M.Brachvogel, M.Niestroj and M.Meurer.(2025).Residual GNSS Ionospheric Error Analysis in Future Low Earth Orbit Applications. 2025 IEEE/ION Position, Location and Navigation Symposium(PLANS), doi:10.1109/PLANS61210.2025.11028459.

How to cite: Do, J.-M., Nam, G., Sun, A. K., and Lee, J.: Residual Ionospheric Errors of the NeQuick-G Model for LEO PNT , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18088, https://doi.org/10.5194/egusphere-egu26-18088, 2026.

A major limitation of using UAV photogrammetry for coastal erosion and geohazard assessment is the effort associated with GCP-based georeferencing. To optimize this, we evaluate the German national PPP-RTK (precise point positioning real-time kinematic) service GEPOS®, provided by the Federal Agency for Cartography and Geodesy (BKG). The focus is on its ability to enable repeatable, GCP-free, and more time-efficient UAV-derived 3D products, suitable for operational upscaling.

In total, we conducted 42 UAV surveys with three platforms (two DJI Mavic 3 Multispectral; RGB imagery only, and one DJI Mavic 3 Enterprise) in 10/2025, covering both nadir-only and multi-view oblique acquisition geometries at an actively eroding cliff section near Wustrow (Baltic Sea coast). Here a former East German military bunker collapsed in February 2024, thus providing a benchmark. GEPOS® corrections were generated by the BKG using three dedicated access points located within the area of interest and at distances of approximately 350 m and 1000 m. This setup enabled an initial sensitivity assessment of repeatability as a function of the correction-access configuration.

In the absence of independent geodetic reference, we focused on repeatability (relative precision). To this end, we compared point clouds and DSMs across near-contemporaneous surveys to avoid impact of surface change. We applied a two-stage evaluation strategy: (i) we quantified end-to-end repeatability from unaligned model-to-model differences, reflecting combined georeferencing and photogrammetric effects; and (ii) removed rigid offsets by masked ICP-based co-registration on a stable concrete reference surface, transferring the derived rigid-body transform to the entire dataset before reassessing residual differences. We assessed distances using M3C2 and robust summary statistics such as Normalized Median Absolute Deviation (NMAD) and 95^th and 99^th percentiles of absolute M3C2 distances after excluding change-prone areas.

Preliminary results indicate that oblique acquisition achieves centimeter-level repeatability without co-registration and improves to around the centimeter scale after co-registration. In contrast, nadir-only surveys show substantially larger inter-model discrepancies prior to co-registration, consistent with predominantly rigid offsets, but converge to low-centimeter residuals after alignment on stable surfaces. The final analysis will quantify repeatability across platforms, acquisition geometries, and correction-access configurations, and evaluate the implications for scaling UAV-based coastal monitoring while minimizing field effort.

How to cite: Anschütz, H., Torizin, J., Schüßler, N., Reschke, P., Schirrmann, T., Fuchs, M., Schütze, K., Rost, C., Neumaier, P., and Mohr, C. H.: Towards scalable, GCP-free UAV photogrammetry using PPP-RTK: repeatability tests at a Baltic Sea cliff site (Wustrow, Germany), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18153, https://doi.org/10.5194/egusphere-egu26-18153, 2026.

The correct resolution of integer carrier-phase ambiguities is a key element for improving user precise positioning solutions, especially during the convergence. However, wrongly fixed ambiguities might deteriorate the solution, so posing a potential threat for safety-critical applications. Within the framework of the Least-squares AMBiguity Decorrelation Adjustment (LAMBDA) method, a Fixed Failure-rate Ratio Test (FFRT) has been proposed to generate ratio-test critical values according to a tolerable failure rate.

For a given failure rate, FFRT thresholds’ computation via Monte Carlo (MC) simulations is generally not computationally efficient. At the same time, with the recent LAMBDA 4.0 toolbox implementation, fitting functions introduced by Hou et al. (2016) were integrated for computing these critical values and therefore controlling the failure rate to prevent unnecessary false alarms. Still, Lookup Tables (LT) represent a conservative approach rather than a close approximation to critical values for a given model strength.

In this contribution we leverage the latest developments in Machine Learning (ML), thus focusing on a Neural Network (NN) function approximation. The latter one considers the components of the ambiguity variance-covariance matrix as input and provides the FFRT critical value for a given failure rate. In this way, it is possible to provide a very accurate approximation (close to MC-based results) with an efficiency comparable to LT approach in use by the latest LAMBDA 4.0 implementation.

For the NN training, several GNSS scenarios are synthetically generated based on actual satellite orbits. Hence, we produce datasets for Precise Point Positioning with Ambiguity Resolution (PPP-AR) user models in an uncombined form, based on a Kalman Filter. It is numerically shown how considering the ‘conditional variances’ as inputs for the NN is sufficient for an approximation of FFRT thresholds, which are otherwise too conservative when using the LT approach developed by Hou et al. (2016). The NN results are therefore assessed based on independent datasets not involved during the training stage.

These three approaches, i.e. MC, NN, LT, are ultimately compared in PPP-AR processing using real data from 30 well-distributed stations from the IGS global network, based on the use of CODE Final products. It is further shown how adoption of fixed critical values for the ratio test, like 2 or 3, often leads to a very conservative ambiguity validation, i.e. returning float solutions when RT is rejected. On the other hand, a properly defined FFRT estimator allows improving user convergence time, as well as enabling more advanced ambiguity validation strategies for PPP-AR, as discussed in this work.

This research has been funded by the ESA’s Navigation Innovation and Support Program (NAVISP) Element 1 programme [https://navisp.esa.int/project/details/307/show].

How to cite: Massarweh, L., Yin, C., Verhagen, S., Liu, X., Odijk, D., Visser, H., and Psychas, D.: A Neural Network approximation of Fixed Failure-rate Ratio Test for PPP Ambiguity Resolution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18444, https://doi.org/10.5194/egusphere-egu26-18444, 2026.

Differential Code Biases (DCBs) are systematic errors, or biases, between two Global Navigation Satellite System (GNSS) code observations at the same or different frequencies. Knowledge of DCBs is required for positioning of GNSS receivers, extracting ionosphere total electron content (TEC), and other applications. Proper knowledge of DCBs is crucial to many navigation applications but also non-navigation applications such as ionospheric analysis and time transfer. The multitude of new signals offered by modernized and new GNSS constellations, requires a comprehensive multi-GNSS bias product. And because of the multitude of GNSS signals it has become more practical to provide the DCBs, differential signal biases, as observable specific biases, OSBs.

At the Navigation Support Office at ESA/ESOC we have for many years relied on the bias products (DCB and OSB) coming from the CODE analysis centre. But in the fast-developing Multi-GNSS landscape it became clear that we needed to have to capability to generate our own independent bias product. For our different GNSS projects we therefore have developed a process to generate our own OSB product with the ambition to have DCBs for all existing MGNSS signals, as long as the signals are tracked by the stations in the large IGS station network. And rather than monthly biases as typically provided and used within the IGS, we have moved to what we call a “Bias Reference Frame” (BREF). The absolute value is still determined by a zero-mean condition at a certain date. But from that point in time the biases are kept stable unless a clear jump in the satellite bias is, automatically, detected. The detectability is at the 0.25ns for well observed biases. The DCB version of the product is publicly available on our Navigation Office website. The OSB version is still under development and testing.

In developing this product, we found some very interesting features of the biases when looking at the biases of the so called “interoperable” signals, which we will present and discuss. We demonstrate the importance of this product for the analysis of the Sentinel 6A data which tracks Galileo and an interesting mix of GPS signals which makes it hard to process the GPS data with the standard IGS products, in particular for PPP-AR.

How to cite: Springer, T., Otten, M., Mayer, V., Gini, F., and Schönemann, E.: Bye-bye, bias! The ESA Multi-GNSS Bias Reference Frame, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19887, https://doi.org/10.5194/egusphere-egu26-19887, 2026.

The use of low-cost Global Navigation Satellite System (GNSS) receivers has emerged as a promising strategy to densify existing geodetic networks and to enhance the spatial resolution of atmospheric monitoring at regional scales. This study presents the deployment and long-term operation of a low-cost GNSS network consisting of five stations installed across the province of Jaén (southern Spain), aimed at complementing the regional permanent GNSS network for the monitoring of atmospheric, climatological and environmental processes. In addition, a sixth low-cost receiver was placed at San Fernando along with the IGS reference station SFER and an operational AEMET meteorological station, enabling direct intercomparisons with high-grade geodetic receiver using meteorological observations to generate atmospheric parameters.

The network has been operating continuously since November 2022. GNSS data were processed using the PRIDE PPP-AR software package up to July 2025, providing precise estimates of the tropospheric total delay. The wet component of the tropospheric delay, combined with in situ surface meteorological measurements, was used to derive precipitable water vapour (PWV) time series for each station. These PWV estimates were systematically compared with independent data sources, including ERA5 reanalysis products and satellite-based post-processed solutions, in order to assess the consistency, stability and accuracy of the low-cost GNSS-derived atmospheric parameters.

The results highlight the capability of low-cost GNSS receivers to capture meaningful atmospheric variability and demonstrate the added value of network densification in regions with different characteristics and sparse permanent instrumentation. The observed differences with respect to coarser-resolution datasets underline the potential of such networks for improving the monitoring and early detection of adverse meteorological phenomena. This study supports the feasibility of using low-cost GNSS technology as a reliable and cost-effective complement to existing geodetic and meteorological observing systems.

How to cite: Rodríguez Collantes, D., de Lacy Pérez de los Cobos, M. C., Garrido Carretero, M. S., and Retegui Schiettekatte, L.: Assessing the Potential of Low-Cost GNSS Network Densification for Regional Atmospheric Monitoring in Southern Spain, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20095, https://doi.org/10.5194/egusphere-egu26-20095, 2026.

In order to meet the demanding accuracy and availability requirements, GPS has introduced L5 signals that are compatible with Galileo E5a signals. These signals are designed to mitigate multipath issues and poor performance in challenging environments such forests and areas affected by jamming. As they are also intended to replace L2 signals in the future, steps must be taken to exploit the modern signal type that is currently broadcast by 20 GPS satellites of blocks IIF and III. This is considered particularly important for some LEO satellites, which rely exclusively on L1/L5 observations.

In addition to standard analysis products based on L1/L2, the CODE (Center for Orbit Determination in Europe) IGS Analysis Center is in the process of testing a prototype processing chain to generate L1/L5-based products, paving the way for GNSS processing to be fully based on L1/L5  signals. The presentation addresses the application of these products to LEO orbit determination and PPP processing of the ground stations, considering different antenna calibrations for IIF satellites. A quantitative validation and comparison with L1/L2-based solutions is also discussed.

How to cite: Kalarus, M., Schaer, S., Dach, R., Arnold, D., and Jaeggi, A.: Analysis of experimental CODE products based on GPS L1/L5 signals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20376, https://doi.org/10.5194/egusphere-egu26-20376, 2026.

Global Navigation Satellite Systems (GNSS) coordinate time series is utilised in geodesy for different purposes, e.g., Earth deformation monitoring. Different signals, such as annual, semi-annual, and draconitic year signals, as well as noise, are superimposed on the GNSS coordinate time series. In addition, a velocity signal caused by plate tectonic movements is present in the horizontal components, and uplift or subsidence exists in the vertical component of the GNSS coordinate time series. We require performing signal separation algorithms to decompose the time series into meaningful signals. In this study, we utilise Monte Carlo singular spectrum analysis (MC-SSA) for signal separation and hierarchical clustering for grouping the modes derived from SSA. We also use least-squares variance component estimation (LS-VCE) and fast LS-VCE for noise determination throughout the whole data processing. Finally, the velocity is determined using least-squares regression after removing the periodic signals and utilising the covariance matrix determined by LS-VCE and fast LS-VCE as a stochastic model. The results are presented in both spatial and temporal domains, which can be used to detect, for example, the phase shift in both domains. The final velocity field and the uncertainty for the up component are also extracted for the GNSS stations in Europe.

How to cite: Karimi, H. and Hugentobler, U.: GNSS coordinate time series analysis and signal separation applied to Earth deformation monitoring, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20523, https://doi.org/10.5194/egusphere-egu26-20523, 2026.

The ionospheric irregularities of the plasma density could significantly cause fluctuations of the intensity, phase, angle of arrival, and polarization state of trans-ionospheric GNSS signals in a rapid and stochastic manner, i.e., ionospheric scintillation, which could lead to communication errors and signal distortions, further seriously threatening the security of the GNSS system and affecting the performance of GNSS high-precision positioning services. Therefore, the mitigation of its impact on the GNSS high-precision positioning service has been a key scientific issue in the field of satellite navigation.

In this study, we proposed a TurboEdit cycle slip detection threshold adjustment method that considers scintillation differences at different latitudes, and constructed a stochastic model considering the ionospheric scintillation information. Through the distribution of cycle slips with regard to the scintillation index, the cycle slip threshold method is initially established for various latitudes; the ionospheric scintillation index calculated from the geodetic GNSS observations is used to construct a stochastic model, which can assign more reasonable weights for the GNSS observations affected by the ionospheric scintillation. Results show that compared with the empirical cycle slip detection threshold, the adjusted cycle slip detection threshold can significantly improve the performance of PPP positioning results in various regions under ionospheric scintillation conditions. Compared with the elevation-angle stochastic model, the improved stochastic model can mitigate the effects of the ionospheric scintillation on PPP solutions in the equatorial ionization anomaly region. This study contributes to enhancing the accuracy, reliability, and integrity of high-precision GNSS applications and services.

How to cite: Liu, H., Ren, X., Chen, P., and Zhang, X.: Leveraging Latitude-Differentiated Thresholds and Weight Optimization to Mitigate the Impacts of Ionospheric Scintillation on GNSS PPP, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20628, https://doi.org/10.5194/egusphere-egu26-20628, 2026.

Real-time estimation of user positioning parameters forms the backbone of high-precision GNSS navigation. The recursive Kalman filter is the most widely adopted estimation method for this task, providing optimal estimates in the minimum variance sense under the assumption that the underlying models are correctly specified. In many practical GNSS applications, however, this assumption may be violated, as measurement models commonly involve state-vector elements that are not naturally linked in time. Imposing incorrect dynamic modeling on such parameters may lead to sub-optimal solutions.

In this contribution, we examine the mechanics of the generalized Kalman filter (Teunissen et al., 2021), which offers a statistically rigorous alternative to the standard Kalman-filter practice of inflating the process-noise variances or assigning arbitrary initial values to states of newly-tracked satellites. Rather than enforcing all state-vector elements to vary in time, the generalized formulation permits only some functions of the state-vector to be linked in time, while others remain unlinked in time. This relaxed dynamic model offers a flexible framework for recursive parameter estimation when limited or insufficient knowledge is available on the temporal behaviour of the involved parameters. Typical applications include purely kinematic precise positioning, network-based satellite clock estimation, kinematic precise orbit determination in low Earth orbit, and GNSS precise positioning during periods with enhanced ionospheric activity.

As any real-time estimation process inevitably requires validation of the underlying models, recursive quality control of the measurement model needs to be executed in parallel with the filter. A direct consequence of the generalized filter is that the classical predicted residuals used in quality control procedures are no longer applicable. It is shown here how these residuals are generalized to predictable functions of the measurements, while practical methods are demonstrated for constructing them in real time for different choices of unlinked-in-time states.

Supported by real-world multi-GNSS simulated kinematic and vehicle-borne datasets, the performance of the generalized Kalman filter using the carrier-phase ambiguity resolution-enabled precise point positioning (PPP-RTK) concept is presented. Next to the positioning performances, the required adaptations to the recursive data quality control procedure, involving both the detection and the identification of mismodeling biases, are illustrated.

Teunissen, P.J.G., Khodabandeh, A. & Psychas, D. A generalized Kalman filter with its precision in recursive form when the stochastic model is misspecified. J Geod 95, 108 (2021). https://doi.org/10.1007/s00190-021-01562-0

How to cite: Psychas, D.: Generalized Kalman filtering applied to real-time high-precision GNSS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21083, https://doi.org/10.5194/egusphere-egu26-21083, 2026.

The Dunaszekcso landslide is one of the major landslides in Hungary located at the right bank of the Danube in the southern part of the country. The landslide shows a retreat of 5-15m per 100 year in the past 2000 years according to geological studies. In this area, the high riverbanks recently experienced major slides, which damaged houses and linear structures. The area has been being monitored for several years using InSAR technique and static GNSS observations, but due to the low temporal resolution of the static GNSS observation campaigns and the lack of frequent absolute displacement control, the InSAR data processing sometimes face significant challenges.

To overcome this problem, we teemed up with European universities, geological services and companies in the GeoNetSee (GeoNetSee – ‘An AI/IoT-based system of GEOsensor NETworks for real-time monitoring of unStablE tErrain and artificial structures’) project (Interreg Danube Region programme, no: DRP0200783), which focuses on developing and testing innovative geodetic approaches for monitoring slope instabilities and infrastructure-related geohazards. Within the GeoNetSee framework, low-cost GNSS receivers are installed at selected slopes, and time series from variometric processing are analysed to identify subtle dynamic and quasi-static displacements caused by environmental loading, rainfall-induced pore pressure changes, and other disturbances. GNSS-derived signals are validated against complementary monitoring methods, including InSAR, traditional geodetic surveys and environmental sensors.

The primary objective of this study is to assess the potential of various GNSS-based observation processing strategies (RTK, fast static, variometric) to detect early deformation signals that may precede landslide events. Low-cost permanent and monitoring GNSS stations were placed on the steep slopes and on the stable ground to monitor the geometrical changes of the slopes and the GNSS observations are analysed with different measurement models and compared to the results of InSAR analysis.

Preliminary results demonstrate that low-cost GNSS techniques are valuable means to detect small-amplitude, short-term slope deformations, indicating changes in stability conditions. These findings highlight the method’s potential as part of integrated slope monitoring and early-warning systems, offering continuous, autonomous, and real-time data that can enhance landslide risk assessment and mitigation strategies in climate-sensitive regions of Central Europe and beyond.

How to cite: Rozsa, S., Turák, B., Kis, A., Bozsó, I., and Török, Á.: Landslide monitoring using permanent low-cost GNSS sensors and InSAR techniques, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21937, https://doi.org/10.5194/egusphere-egu26-21937, 2026.

High-precision GNSS services typically rely on dense reference networks to model atmospheric delays effectively. However, maintaining such infrastructure is often impractical in vast or developing regions. This study evaluates the feasibility of Precise Point Positioning with Ambiguity Resolution (PPP-AR) using a minimal network configuration consisting of only four Continuously Operating Reference Stations (CORS).

We focus on quantifying the spatial degradation of positioning accuracy as the distance from the reference network increases. By generating corrections from this sparse cluster, we analyze performance metrics including convergence time, fixing rate, and coordinate precision across rovers located at varying baselines from the network centroid.

The results demonstrate a clear correlation between distance and accuracy degradation, specifically highlighting the impact of residual ionospheric and tropospheric errors. Despite this degradation, the study confirms that PPP-AR can maintain reliable centimeter-level positioning well beyond the limits of traditional Network RTK (NRTK). These findings provide empirical guidelines for deploying cost-effective GNSS infrastructure with optimized station density.

How to cite: Skakun, I., Abanosimov, V., Sviridov, A., and Suvorkin, V.: Validating PPP-AR Performance in Sparse Infrastructure: A Case Study with Four Reference Stations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21941, https://doi.org/10.5194/egusphere-egu26-21941, 2026.

Smartphones have evolved into ubiquitous platforms equipped with a sophisticated array of sensors, including cameras, IMUs, GNSS receivers, LiDAR, and magnetometers. These sensors enable a wide range of applications, from navigation and mapping to virtual reality and accessibility tools for the visually impaired. However, despite this hardware potential, the development of robust multi-sensor fusion algorithms remains constrained by data limitations.

While existing public datasets—such as those from the Google Smartphone Decimeter Challenge (GSDC)—have advanced high-accuracy positioning by integrating GNSS and IMU data, they often overlook complementary sensors like cameras and magnetometers. Furthermore, current data collection tools (e.g., GNSSLogger, Sensor Logger) often lack the capability to log raw GNSS observations and visual data simultaneously with precise time synchronization. This gap hinders the application of emerging machine learning techniques that require diverse, synchronized input streams.

In this contribution, we introduce a custom Android application capable of collecting time-synchronized data from multiple sensors, including IMU, camera, GNSS, and magnetometer. We evaluate the time-synchronization capabilities of popular smartphone models, including the Google Pixel series, Xiaomi, Samsung, and OnePlus. Using this application, we compiled a comprehensive dataset in Calgary, Alberta, Canada, capturing diverse environments such as urban canyons, highways, parks, and farmland under varying weather conditions. The data includes both vehicle-mounted and handheld kinematic scenarios. Finally, to demonstrate the utility of the dataset, we establish a performance benchmark using conventional open-source software, such as VINS. This work provides the research community with a holistic benchmark dataset to advance multi-sensor fusion algorithms for smartphones.

How to cite: Yang, H. and Nie, S.: Multi-Sensor Smartphone Mapping and Positioning: App, Dataset, and Benchmark, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22106, https://doi.org/10.5194/egusphere-egu26-22106, 2026.

Precise orbit determination (POD) is a fundamental requirement for satellite navigation, Earth observation, and space applications. Conventional POD methods typically depend on external initial orbit states and clock corrections, which limit resilience and may introduce external biases. Here, we demonstrate a resilient POD method that depends solely on observations from the third generation BeiDou Navigation Satellite System (BDS-3) without requiring any external initial orbit and clock information. Reliable initial orbit states are internally obtained through a global network solution of double-differenced code observations with robust estimation. Using one year of data collected from about 200 BDS-3 tracking ground stations in 2024, initial orbit position and velocity accuracies reach approximately 0.5 km and 0.1 m/s, respectively. Based on these initial orbit states and a zero-mean clock constraint, a two-step scheme is then applied to realize the joint precise determination of satellite orbits and satellite clock corrections. The resulting orbits achieve an accuracy of up to 4.5 cm, in terms of the standard deviation (STD) of satellite laser ranging (SLR) residuals. These results confirm the feasibility of fully resilient BDS-3-only POD without reliance on external initial conditions, enabling independent and robust satellite navigation.

How to cite: Chen, X., Ge, M., Zhang, X., and Schuh, H.: BDS-3-Only Precise Orbit Determination Without External Initial Orbit and Clock Corrections, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1355, https://doi.org/10.5194/egusphere-egu26-1355, 2026.

Space safety is becoming an increasingly important topic for our society, in particular with respect to space debris. According to the ESA's Space Environment Report 2025, the number of satellites, and, consequently the amount of space debris, particularly in low Earth orbits (LEOs) is growing rapidly. To ensure that satellite operators are informed about the need for evasive manoeuvres, it is necessary to implement countermeasures such as the identification and monitoring of space debris. Knowing the approximate positions of space objects to be tracked via Satellite Laser Ranging (SLR) is essential for aligning the SLR station's pointing accordingly. Accurate orbit predictions for satellites are provided to the stations by prediction centres. But this does not apply to space debris. Instead, the so-called two-line elements (TLEs) are used to predict the orbits of these objects. TLEs contain important orbital elements which are related to position and velocity of the space object at a specific time or point. However, they are limited in their accuracy which results in inaccurate orbit predictions. To achieve a more precise laser alignment for space debris tracking, we present an approach to improve the accuracy of orbit predictions based on TLEs, using the SLR functionality of the GROOPS (Gravity Recovery Object Oriented Programming System) software toolkit. Furthermore, we demonstrate that incorporating real-time measurements can enhance the accuracy of orbit predictions for station pointing alignment in subsequent passes.

How to cite: Suesser- Rechberger, B., Mayer-Guerr, T., Krauss, S., Tieber-Hubmann, C., Wang, P., and Steindorfer, M.: Improving station pointing alignment for SLR using approaches based on TLEs and real-time measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2834, https://doi.org/10.5194/egusphere-egu26-2834, 2026.

Using the high-quality GNSS observations of the low Earth orbiting Swarm constellation, Delft University of Technology routinely delivers precise science orbits (PSO), aerodynamic accelerations, and thermosphere densities for all three satellites within the framework of the Swarm Data, Innovation, and Science Cluster. The PSO consist of a reduced-dynamic orbit to precisely geotag the onboard magnetic and electric field instrument observations and a kinematic orbit with covariance information to determine the large-scale time variable changes of Earth’s gravity field. The GNSS-derived densities can be used to improve thermosphere models and for studying the influence of solar and geomagnetic activity on the thermosphere. The aerodynamic accelerations are used to augment the higher-resolution accelerometer data, which are affected by accelerometer instrument issues. Due to these issues, the accelerometer-derived thermosphere densities are not continuously available for all satellites.

For both PSO and density products, the nominal processing strategy has recently been improved. The PSO processing strategy, which includes a realistic satellite panel model for solar and Earth radiation pressure modelling and integer ambiguity fixing, was updated with a new approach to reduce the impact of ionospheric scintillation-induced errors in the kinematic orbits. The previous procedure was not properly tuned for high solar activity conditions, resulting in many gaps in the kinematic orbits, with losses of up to 40% during periods with such conditions. With the new approach, considerably more kinematic orbit data are available.

For the GNSS-based thermosphere density retrieval, aerodynamic accelerations are estimated in a precise orbit determination using a Kalman filter approach and converted to densities using a high-fidelity satellite geometry model and gas-surface interaction modelling. To account for the large variations in the encountered aerodynamic signal by the Swarm satellites over the mission lifetime, a new approach was implemented that uses adaptive process noise settings for the estimated aerodynamic accelerations. These new settings lead to significantly improved densities during low-density signal conditions.

The new Swarm precise orbit products (version 0203) and thermosphere density products (version 0301) are available for users at the dedicated ESA Swarm website (https://swarm-diss.eo.esa.int). The Swarm densities are also available at our thermosphere density database (https://thermosphere.tudelft.nl).

How to cite: van den IJssel, J., Siemes, C., and Visser, P.: New GNSS-derived precise orbits and thermosphere densities for the Swarm satellite constellation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4843, https://doi.org/10.5194/egusphere-egu26-4843, 2026.

Precise orbits of Low Earth Orbit (LEO) satellites are the prerequisite for various precise applications with LEO satellite/constellations. Typically, centimeter-level LEO satellite orbit products can be obtained using onboard GNSS observation data. However, with the arrival of the 25th solar activity peak year and the cost control of commercial LEO satellites on manufacturing costs, traditional methods for onboard GNSS data processing need further improvement. In terms of data preprocessing, due to the severe ionospheric variations caused by solar activities, traditional cycle slip detection models are prone to frequent false detections of cycle slips during ionospheric active periods, leading to a decline in the accuracy of LEO satellite orbit determination. This study analyzes the variation characteristics of ionospheric disturbances, and proposes a polynomial fitting prediction method with ionospheric variation constraints, which can effectively distinguish cycle slips from ionospheric variations and improve the LEO satellite orbit determination accuracy under ionospheric disturbances. The results show that with the constraints of ionospheric variation, the RMS values of orbital errors for GRACE-C in along-track, cross-track, and radial components are improved by 11%, 17%, 6%, respectively. As for the optimization of GNSS observation model for low-cost LEO satellite, this study proposes a GNSS observation model considering the time-varying characteristics of onboard receiver biases, which can effectively enhance the stability of onboard receiver clock offset solution and ensure the accuracy of LEO satellite orbit as well. The results show that new model can reduce the discontinuities of arc-boundary for receiver clock from tens of nanoseconds to sub-nanosecond levels. In terms of frequency stability, the new model shows the similar short-term stability to the conventional model while notable improvements in medium- and long-term stability (beyond 10²s).

How to cite: Ge, H., Wu, T., Meng, G., and Li, B.: Optimizing GNSS observation model with onboard receiver for LEO precise orbit determination , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4875, https://doi.org/10.5194/egusphere-egu26-4875, 2026.

The ESA's GENESIS mission, scheduled for launch in 2028, collocates the four geodetic techniques (DORIS, GNSS, SLR and VLBI) on a single spacecraft, with accurate calibration of the platform and instruments, and a shared clock/frequency source for the active instruments. To assess the expected performance of this mission, we perform end-to-end simulation studies using the GINS/DYNAMO software developed at CNES. Our analysis examines how multi-technique GENESIS observations could contribute to the determination of the Terrestrial Reference Frame (TRF) and Earth rotation parameters, as well as to the detection of inter-technique biases. The simulations acccount for technique-specific error sources, dynamical modeling and instrument calibration uncertainties to assess realistic scenarios. We examine the use of the common orbit as a link between techniques to evaluate how multi-technique combined GENESIS-like solutions at the observation level affect the TRF parameters, in particular the origin and scale, and the inter-technique consistency within the combined TRF solutions.

How to cite: Aït-Lakbir, H., Chatzinikos, M., Delva, P., Marty, J.-C., and Pollet, A.: Numerical simulations on GENESIS' contribution to the determination of terrestrial reference frame (TRF) parameters, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4882, https://doi.org/10.5194/egusphere-egu26-4882, 2026.

The Copernicus Precise Orbit Determination (CPOD) Service is key to the Copernicus Sentinel missions, supporting Sentinel-1, -2, -3, and -6 with precise orbit products and auxiliary data. These products enable the operational generation of scientific data at ESA and EUMETSAT and are distributed via the Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).

For high-accuracy POD, radiation pressure modelling is a major contributor to orbit errors, particularly for platforms with complex geometries. Sentinel-6 represents a challenging case, as its structural configuration is poorly represented by conventional macro-models, leading to persistent signatures in the estimated empirical accelerations used to absorb unmodelled dynamical effects.

Within the CPOD context, GMV has been investigating an alternative radiation modelling strategy using the GMV Grial tool. The approach relies on a surface projection algorithm that computes radiation forces directly from a detailed spacecraft three-dimensional model, provided in CAD format, together with associated optical and infrared material properties. The resulting adimensional force coefficients are tabulated in the satellite reference frame as a function of the azimuth and elevation of the incident ray, allowing efficient integration into operational POD workflows. The methodology targets improved modelling of solar radiation pressure, as well as Earth albedo and infrared radiation pressure effects.

The methodology has been successfully applied and validated for Sentinel-3, demonstrating good agreement between modelled and estimated accelerations for box-wing-type spacecraft. Its extension to Sentinel-6 is currently under assessment. This work presents the modelling framework, validation strategy, and first Sentinel-6 results. While no significant reduction of empirical acceleration signatures is yet observed, the results indicate a strong sensitivity to assumed geometry and surface properties, highlighting the need for improved spacecraft characterisation from spacecraft manufacturers to fully exploit advanced radiation modelling techniques.

How to cite: Fernandez Sanchez, J., Lara Espinosa, S., Fernandez Martin, C., Peter, H., Pinheiro, M., and Nogueira Loddo, C.: COPERNICUS POD SERVICE: Radiation modelling based on 3-D model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8923, https://doi.org/10.5194/egusphere-egu26-8923, 2026.

DORIS data processing is sensitive to the short-term clock variations, but the onboard clock corrections can be obtained from DORIS pseudoranges alone only as a polynomial model covering a couple of days. The Sentinel -3A and -3B satellites are the very first ones where the DORIS and the GNSS equipment are running on the same onboard oscillator. This offers the unique opportunity to synchronize the onboard clocks epoch-wise using GNSS and thus to measure clock behavior in detail and to make use of the short-term clock behavior in the DORIS data analysis. A similar approach can be applied also for Sentinel-6A on Jason orbit.

GPS-derived epoch-wise clock corrections are computed for the ultra-stable oscillator (USO) and introduced as fixed into the DORIS data processing making DORIS processing capable of considering the short-term variations of the satellite clock. This approach is very promising for studying the South Atlantic Anomaly (SAA) effect. In addition, the tandem phase of the satellite pairs Sentinel-3A and 3B (130 days) and Sentinel -6A and Jason -3 (~330 days) offer additional opportunities to perform closure measurements using same beacons observed synchronously by both satellites.

This poster will visually illustrate these concepts and techniques along with the results of Sentinel -6 with integrated GNSS clocks, the mapping of the SAA effect, the tandem phase analysis results and the near future plans and benefits of GNSS-DORIS combination for precise orbit determination.

How to cite: Gunasekaran, B. K., Štěpánek, P., Filler, V., and Hugentobler, U.: Ingestion of GNSS-derived clock parameters into DORIS data analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11173, https://doi.org/10.5194/egusphere-egu26-11173, 2026.

The attitude motion of geodetic satellites can indirectly affect their orbit through non-gravitational perturbations. This effect is particularly significant for non-symmetrical bodies, as their orientation determines the surface areas subjected to atmospheric drag and radiative forces. However, this also applies, to a lesser extent, to fully spherical satellites due to thermal effects such as the Yarkovsky effect (Bertotti and Iess, 1991; Farinella et al., 1996; Métris et al., 1999; Andrés et al., 2004). Modelling the Yarkovsky effect requires, in particular, knowledge of the spin axis direction.

Due to the peculiar configuration of Ajisai mirrors, the photometry of flashes generated by the reflection of sunlight on their surfaces, and specifically the linear measurement of its luminous flux, appears to be the most adequate technique to study its rotation with high single-pass accuracy. Measurements of the Ajisai's luminous flux has been acquired using a high frequency (10 kHz) linear-detection optical photometry technique from the MéO telescope at Grasse station on the Plateau de Calern site of Observatoire de la Côte d'Azur. In this presentation we show that this instrumentation produces very rich informations. 

The selection, extraction, time-stamping and collection of the sequence of single flashes from the raw measured flux and the subsequent identification of the mirror on which the reflection occurred, allowed us to determine the rotation parameters of the satellite, i.e. to reconstruct its attitude, with an unprecedented single pass accuracy. The estimated precision for the determination of the rotation parameters during one pass of Ajisai is typically in the order of 0.25 deg for the spin axis orientation, 10^-5 s for the rotation period.

The growing number of kHz-capable Satellite Laser Ranging Stations and the extensive dataset made available by the International Laser Ranging Network (ILRS) position kHz SLR as a compelling tool with great potential for conducting medium- and long-term studies on the rotation of the Ajisai satellite.

Through the analysis of high repetition rate laser ranging data from the ILRS network, we were able to further investigate the rotation and confirm the photometry results. Similar to photometry, the sequence of CCRs closest approaches during the satellite pass observation could be identified and used to reconstruct the satellite's attitude.

A notable application of this work could be in the context of the next generation bistatic optical time transfer through a fully passive satellite.

How to cite: Calatroni, C., Métris, G., Courde, C., Phung, D.-H., Chabé, J., Aimar, M., Maurice, N., Mariey, H., and Scariot, J.: Determination of the rotation parameters of the AJISAI passive satellite using linear detection photometry and kHz SLR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12632, https://doi.org/10.5194/egusphere-egu26-12632, 2026.

For the last few years, Dionysos Satellite Observatory (DSO) of the National Technical University of Athens (NTUA) has undertaken the challenging task of developing a new, open-source and free software toolkit to facilitate the processing of DORIS observations for Precise Orbit Determination (POD) and positioning. The ongoing objective is to eventually deliver a state-of-the-art software to the scientific community, focusing on a fundamental technique of satellite geodesy. The significance of this technique across various geoscience disciplines is well-established and demonstrated by extensive publications in fields such as reference frames, altimetry, and geodynamics, among others. The software itself is designed in a way that accommodates scientific research, experimentation and validation, since it is generic enough to handle multiple data sources and models. Care is taken to design for efficiency and robustness, yet favouring re-usability and modularity, leveraging along the way modern software design principles. Additionally, we adopt modern standards and refined modeling approaches.

Analysis highlights include a rigorous treatment of the DORIS Doppler observation equation, dynamic orbit modeling, usage of the Extended Kalman Filter with process noise and state-of-the-art models and algorithms to handle tidal and non-tidal phenomena. Various validation tests are performed and presented, both for intermediate steps (e.g. different forces acting on the satellites) as well as using the estimated trajectories with respect to high-quality results from IDS Analysis Centers. In this study, we present preliminary results obtained using the toolkit, provide insights into its architecture and capabilities, and outline our immediate next steps.

How to cite: Anastasiou, D., Papanikolaou, X., Serelis, G., Fisikopoulos, V., Krey, V., Zacharis, V., and Tsakiri, M.: Developing an Open-Source Toolkit for Precise Orbit Determination and Positioning Using DORIS, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14906, https://doi.org/10.5194/egusphere-egu26-14906, 2026.

Laser Inter-Satellite Links (LISL) are increasingly pivotal for next generation GNSS, offering high precision ranging with low power and high directionality, while reducing dependence on global ground tracking distribution. This study presents a simulation based Precise Orbit Determination (POD) analysis for the BDS-3 constellation augmented by LISL constraints. We focus on a practical link scheduling strategy under visibility constraints and evaluate how LISL observations strengthen orbit and clock estimation, particularly when ground tracking is limited.

A feasible LISL topology is designed for the BDS-3 MEO constellation based on precise ephemerides. On same orbit plane links are organized into a closed-loop ("hand-in-hand") geometry to stabilize the configuration. The links on different orbit plane employ a dynamic time varying allocation strategy, reserving capacity to flexibly connect with IGSO satellites and adjacent MEO planes, thereby enhancing cross-plane connectivity. Link feasibility is validated using an Earth-occlusion and atmospheric tangency model. To mitigate relative clock errors, dual-way ranging is applied to separate geometric distance from clock offsets. Based on this configuration, LISL observations are simulated to generate adjacency matrices and distance time series for assessing geometric stability.

POD experiments were conducted for DOY 197–227, 2023, under two scenarios: (1) a global network using MEGX stations, and (2) a regional network utilizing eight iGMAS stations in China. The dynamic model employs ionosphere-free combinations and standard CODE dynamic strategies, including solar radiation pressure, Earth albedo , and antenna thrust models. LISL ranges are introduced as constraints with 1 mm a priori precision.

Results demonstrate that LISL constraints significantly enhance both orbit and clock estimation, with the most substantial gains observed in the regional tracking scenario. Validated against CODE precise products, clock accuracy improves from 0.086 ns to 0.068 ns, with smoother overlapping Allan deviation. For the global network, the 3D orbit RMS decreases from 5.0 cm to 4.2 cm. For the regional network, where GNSS-only solutions are limited to decimeter-level accuracy, adding LISL reduces the along-track, cross-track, and radial RMS by 80.8%, 76.5%, and 74.0%, respectively (82.5% improvement in 3D RMS). Independent Satellite Laser Ranging (SLR) residuals confirm these improvements, highlighting the potential of LISL to ensure robust, high-precision orbit products for future autonomous navigation.

How to cite: Jiang, C., Chen, H., Zhou, X., and Jiang, W.: Precise orbit determination supported by BDS-3 with laser inter-satellite links : A simulation study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16615, https://doi.org/10.5194/egusphere-egu26-16615, 2026.

Satellite Laser Ranging (SLR) is a fundamental technique of space geodesy, providing essential contributions to the realization and long-term stability of terrestrial reference frames. For future multi-technique missions such as the GENESIS mission, a realistic assessment of achievable SLR observation yield requires modelling approaches that reflect operational constraints of the global tracking network.

This study presents an operation-informed simulation framework for estimating the SLR observation yield of the International Laser Ranging Service (ILRS) network. The approach represents tracking opportunities using station availability windows (SAWs) derived from geometric visibility and integrates weather-gated availability based on ERA5 reanalysis data. Empirical models of tracking duration, interleaving behaviour, and station-specific priority patterns are derived from historical ILRS normal point records. The framework explicitly avoids optimal scheduling and instead aims to reproduce realistic network behaviour over annual time scales.

The framework is applied to a representative GENESIS mission scenario and evaluated using network-level performance indicators, including annual union tracked time, normal point (NP) count, and NP gap statistics. Comparisons with historical SLR tracking of LAGEOS-1/2 demonstrate that the simulated GENESIS observation yield lies within a realistic reference range.

The proposed framework provides a practical tool for mission performance assessment and scenario analysis of space-geodetic observing systems.

How to cite: Gao, Y. and Montenbruck, O.: Operation-informed simulation of ILRS Satellite Laser Ranging observation yield for the GENESIS mission, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16868, https://doi.org/10.5194/egusphere-egu26-16868, 2026.

Future ‘space-tie’ satellite missions such as Genesis aim at co-locating multiple space-geodetic techniques on a single satellite platform to improve the consistency and long-term stability of the Terrestrial Reference Frame (TRF). However, quantifying the benefits of such satellite-based co-location requires not only advanced simulation capabilities, but also a robust validation of real observation data using consistent multi-technique processing strategies. Already today, missions such as the Sentinel satellites provide an opportunity to realise satellite-based co-location by carrying multiple space-geodetic observation techniques onboard.

To date, most multi-technique Precise Orbit Determination (POD) approaches rely on orbit determination approaches in which the TRF is fixed and, in the case of Global Navigation Satellite Systems (GNSS) Low Earth Orbit (LEO) POD, GNSS constellation orbits and clocks are typically held fixed as well. Consequently, cross-technique interactions and their impact on GNSS constellation orbits and clocks, LEO orbits, Earth Rotation Parameters (ERPs), and the TRF have so far not been comprehensively assessed for all space-geodetic techniques. Investigating these effects using real observations is therefore a crucial step that can already be performed prior to Genesis.

In this study, we investigate an integrated multi-technique POD approach using real GNSS, Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), and Satellite Laser Ranging (SLR) tracking data. The analysis covers the multi-technique LEO satellites Sentinel-3A, Sentinel-3B, and Sentinel-6A (MF), together with the GPS and Galileo constellations over a two-year period. Using GFZ’s in-house software EPOS-OC, LEO and GNSS constellation orbits and clocks, the TRF, and ERPs are estimated simultaneously within a single adjustment, fully consistent with respect to dynamic and geometric modelling.

A stepwise integration is performed, starting from single-technique LEO POD solutions and proceeding to the integration into a combined GNSS constellation solution using GNSS observations only. DORIS and SLR observations are incrementally added to assess their impact on LEO orbits, GNSS constellation orbits and clocks, ERPs, and ground station coordinates.

The results provide a real-data-driven assessment of integrated multi-technique POD for satellite-based co-location and form a basis for subsequent Genesis end-to-end simulation studies and future Genesis real-data processing.

How to cite: Schreiner, P., Glaser, S., König, R., Neumayer, K. H., Flechtner, F., and Schuh, H.: Integrated Multi-Technique Precise Orbit Determination Using GNSS, DORIS and SLR: A Real-Data-Based Assessment for Future Co-location in Space Missions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17918, https://doi.org/10.5194/egusphere-egu26-17918, 2026.

In recent years, the use of non-scientific low Earth orbiting (LEO) satellites for gravity field determination has been increasingly explored. In principle, the same methods as for non-dedicated scientific missions are applied by analysing the satellites’ orbital perturbations to gain information about the Earth’s gravity field. 

With currently over 100 CubeSats in orbit, the Spire commercial constellation provides a huge amount of GNSS tracking data in the same timeframe as scientific missions.  This can be exploited to increase the spatio-temporal resolution of estimated gravity field solutions. Although the data quality is limited, previous analyses using data from a 2020 ESA Announcement of Opportunity project have shown that a combined processing of Spire CubeSats can achieve monthly gravity field solutions of similar quality as non-dedicated scientific missions. In our work, we make use of both the Spire data from 2020 and a new dataset from 2023 provided by EUMETSAT. 

At the Astronomical Institute of the University of Bern, non-gravitational forces acting on the satellite have so far not been explicitly modelled when determining the gravity field, but instead absorbed by pseudo-stochastic parameters such as piecewise constant accelerations. As these forces are prominent for CubeSats due to their low altitude and their large area-to-mass ratio, this study explores how the estimation of the orbits and gravity field solutions improves when explicitly modelling these forces. To achieve this, we determine kinematic orbit positions from Spire CubeSat GNSS phase and code data and introduce them as pseudo-observations in an orbit and gravity field recovery step, where dedicated non-gravitational force modelling is applied using macro-model information provided by Spire. The combination of the different Spire satellites is performed at the normal equation level using a least-squares approach. 

How to cite: Miller, A., Arnold, D., Grombein, T., Lasser, M., and Jäggi, A.: Gravity field determination from Spire CubeSat data with non-gravitational force modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18446, https://doi.org/10.5194/egusphere-egu26-18446, 2026.

Inertial navigation is essential for space missions due to its independence from external signals and references. Inertial navigation systems (INS) rely on accelerometers and gyroscopes to track changes in velocity and orientation, allowing spacecraft to determine their trajectories independently—provided that gravitational accelerations are sufficiently well modelled. However, conventional electrostatic accelerometers used in current space missions typically suffer from significant low-frequency noise and drift, particularly below 10⁻³ Hz, which limits long-term navigation accuracy and orbit determination performance. Quantum inertial sensing based on atom interferometry, on the other hand constitute an attractive alternative technology, based on a fundamentally different measurement principle. By exploiting the wave nature of matter, quantum sensors enable highly precise and drift-free measurements of non-gravitational acceleration, with the potential to substantially improve orbit determination. In addition, the microgravity environment in space allows for interrogation times that are orders of magnitude longer than on Earth, leading to significantly enhanced sensitivity compared to terrestrial implementations of quantum sensors.

In this work, we present our developed,  comprehensive model for multi-axis quantum accelerometers and gyroscopes based on the schemes which are expected to perform best under the microgravity conditions of space. In particular, our modelling accounts for different sources of noise and systematics such as the detection noise, laser frequency noise, wavefront aberration, and sources of contrast loss. It also considers the combined effect of spacecraft rotation around all its axes, gravity gradients, and self-gravity on the measurements of the sensors. Using this framework, we simulate quantum inertial sensor measurements for Earth-orbiting satellites and along an Earth–Moon transfer trajectory, enabling an assessment of their performance for Earth-orbiting and lunar mission scenarios. The resulting simulations are used to evaluate the performance of quantum accelerometers and gyroscopes under different assumptions and scenarios in space. The goal of this work is to identify the challenges associated with deploying quantum inertial sensors for space navigation, to discuss potential mitigation strategies, and to quantify the benefits these sensors could provide for future spacecraft navigation and orbit determination.

How to cite: HosseiniArani, A., C. Sreekantaiah, A., Beaufils, Q., Pereira dos Santos, F., He, X., Hugentobler, U., and Schön, S.: Challenges and Benefits of Quantum Sensors for Inertial Navigation in Space, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18902, https://doi.org/10.5194/egusphere-egu26-18902, 2026.

Accurate measurement of Earth’s energy imbalance (EEI) is one of the central challenges in climate science.  At present, global and regional EEI variability is inferred from radiometric measurements, anchored with time-mean planetary energy inventory estimates due to sensor absolute calibration biases. Space dynamics methods for EEI estimation have been investigated since the 1970s, notably with the CASTOR/CACTUS accelerometers, whose performance exceeded expectations. It led to the BIRAMIS project which aimed at directly measuring EEI from accelerometer observations of the Earth Radiation Pressure (ERP).

In this study, we investigate an alternative space-dynamics–based approach to infer time-mean EEI and anchor CERES. The method aims to provide an alternative anchoring method by directly correcting the absolute calibration error of the CERES radiometers with the introduction of an adjustable scaling parameter applied to the ERP acting on passive spherical satellites tracked by Satellite Laser Ranging (SLR). This method is expected to substantially improve the accuracy of CERES observations, reducing the current accuracy of ±2.5 W.m-2 over a decadal timescale to a target accuracy of a few 0.1 W.m-2 on an annual basis. 

To assess the accuracy of this method, we focus on Ajisai, a Japanese geodetic satellite launched in 1986. Ajisai is a suitable candidate due to its altitude of approximately 1500 km, its area-to-mass ratio, which is nearly an order of magnitude larger than that of most other geodetic satellites, and its spin-stabilized configuration. To evaluate the feasibility and relevance of the approach, we simulate SLR observations, allowing us to introduce controlled errors both in the measurements and in the force models.

In this study we account for error sources from gravity field and tidal models, atmospheric drag, the Yarkovsky effect, SLR measurement noise, and station-related errors. As expected, the results show that the estimate of the time-mean EEI is primarily affected by uncertainties in atmospheric drag and the Yarkovsky effect. A parameter sensitivity study was conducted to identify optimal strategies for mitigating these errors. The time-mean EEI estimate is also sensitive to anisotropic effects arising from Ajisai’s non-perfect spherical symmetry, which introduce a non-negligible bias.

Overall, we establish an error budget for this new method and demonstrate the estimate of the time-mean EEI from SLR measurement is feasible. The quantitative results suggest this approach could be sufficiently precise to anchor CERES at a better precision than currently done with the planetary inventory. 

How to cite: Chapiron, A., Couhert, A., and Meyssignac, B.: Feasibility study of a time-mean Earth energy imbalance estimate derived from Satellite Laser Ranging measurement of the Earth Radiation Pressure , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19862, https://doi.org/10.5194/egusphere-egu26-19862, 2026.

Galileo satellite surface properties are published by the European GNSS Service Center (GSC) as part of the official satellite metadata. These properties describe surface elements that are grouped into four main categories: multi-layer insulation (MLI), optical radiators, navigation antennas, and solar cells. Based on this information, a simple box-wing solar radiation pressure (SRP) model is widely applied by the International GNSS Service (IGS) analysis centers (ACs) for Precise Orbit Determination (POD).

However, key thermal effects, such as radiator emission and imbalanced thermal radiation from navigation antennas and solar panels, are typically neglected, as detailed thermal information is not publicly available. Instead, these effects are partially absorbed by the Empirical CODE Orbit Model (ECOM/ECOM2) parameters, which are widely estimated to compensate for deficiencies in the physical force modeling.

In this contribution, we develop advanced macro models for Galileo satellites, including refined SRP and Earth radiation pressure (ERP) models based on a more detailed representation of satellite surface elements, as well as thermal radiation models for radiator emission, navigation antennas, and solar panels using best-guess values. The impact of each individual thermal force component on POD and terrestrial reference frame solutions is assessed. The final results are compared against the standard GSC-based box-wing model.

Given the complexity of the physical macro models, we introduce acceleration tables for Galileo In-Orbit Validation (IOV) and Full Operational Capability (FOC) satellites as generic interface between macro models and the orbit integrator. The tables provide non-gravitational accelerations as functions of satellite orbital argument and Sun elevation angle above orbital plane, including both SRP and thermal radiation effects. Earth radiation pressure is excluded from the tables due to its pronounced temporal variability and should therefore be modeled separately.

How to cite: Duan, B., Hugentobler, U., and Dach, R.: From macro models to generic acceleration tables: modeling non-gravitational forces acting on Galileo satellites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20449, https://doi.org/10.5194/egusphere-egu26-20449, 2026.

The interplay between the length of day (LOD) and the El Niño–Southern Oscillation (ENSO) has been investigated in geophysical research since the 1980s. LOD, defined as the negative time derivative of UT1-UTC, is intrinsically linked to the Earth Rotation Angle (ERA), a fundamental Earth Orientation Parameter (EOP).

ENSO, a dominant climate mode in the tropical eastern Pacific, substantially influences tropical and subtropical regions. Extreme ENSO episodes are associated with significant hydroclimatic anomalies across multiple regions, including severe droughts and floods. These events evolve over extended incubation periods, during which interannual fluctuations in LOD and the angular momentum of the atmosphere (AAM), ocean (OAM), and lithosphere/hydrogeosphere (HAM) are modulated by complex ocean–atmosphere interactions.

Key manifestations of ongoing climate change, such as rising global temperatures and sea levels, are strongly modulated by ENSO. Interannual variability in global mean sea surface temperature (GMST) and global mean sea level (GMSL) further reflects Earth's rotational dynamics changes.

This study aims to elucidate the interannual (2–8 years) couplings between LOD, AAM, OAM, HAM, and selected climate indices, including the Southern Oscillation Index (SOI), Oceanic Niño Index (ONI), GMST, and GMSL. The influence of these climate signals on LOD from 1976 to 2024 will be assessed using advanced semblance analysis, exploring multiple methodological variants based on the continuous wavelet transform to capture correlations across both temporal and spectral domains.

A detailed understanding of these interactions enhances our knowledge of Earth’s dynamic system, informs geophysical modeling efforts, and improves the precision of applications that rely on accurate timekeeping and measurements of Earth’s rotational behaviour. 

How to cite: Staniszewska, D. and Wińska, M.: Length of Day Variability and Climate Indicators: Insights from ENSO Events , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-631, https://doi.org/10.5194/egusphere-egu26-631, 2026.

Variations in terrestrial water storage (TWS), as observed by the GRACE/GRACE-FO  missions, provide unique insights into large-scale hydrological processes. However, translating these satellite observations into transport parameters such as surface diffusivity, lateral water fluxes, and groundwater recharge remains challenging. In this study, we propose using a surface diffusion-advection model coupled with a WGHM data assimilation framework of gridded GRACE solutions to estimate subsurface diffusivity and systematic precipitation–evapotranspiration biases simultaneously. The global kinematic hydrology model represents the lateral and vertical transport of water by diffusion, while GRACE observations represent the total water storage. In the steepest descent 4D Var-like procedure, the parameter gradients of the objective function are computed using the hydrological model's adjoint. Errors on derived diffusivities are also computed. The optimised parameters enable us to diagnose effective surface diffusivity and lateral water fluxes, as well as net groundwater recharge. This framework provides a physically consistent interpretation of GRACE-observed mass redistribution and offers new perspectives on large-scale hydrological transferts.

How to cite: Ramillien, G., Darrozes, J., and Seoane, L.: Estimation of surface hydrological diffusivity and atmospheric flux bias using GRACE satellite data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4049, https://doi.org/10.5194/egusphere-egu26-4049, 2026.

How to cite: Blazquez, A., Meyssagnac, B., Fourest, S., and Duvignac, T.: Satellite gravimetry and altimetry combined with in-situ ocean temperature profiles enable to close the Earth energy budget and track yearly global energy anomalies from top of the atmosphere to the ocean, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6539, https://doi.org/10.5194/egusphere-egu26-6539, 2026.

Coastal zones face increased risks from the combined effects of climate-driven sea-level rise and vertical land motion (VLM), which together determine rates of relative sea-level (RSL) change. While oceanic contributions to RSL are increasingly well monitored and projected, land subsidence (i.e., negative VLM) remains one of the least systematically observed and most spatially heterogeneous components of RSL, despite its potential to locally exceed climate-driven ocean rise by an order of magnitude. This observational gap is especially pronounced in rapidly urbanizing and data-limited regions, where sparse tide-gauge and GNSS networks hinder the identification of subsidence hotspots and their evolving impacts on coastal risks.

In this talk, I present a framework that leverages satellite geodesy as a climate observing system to resolve the spatiotemporal dynamics of land subsidence and quantify its contribution to present and future relative sea-level change, using Java Island, Indonesia, as a regional-scale case study. We generated high-spatial resolution (75 m) contemporary VLM fields from using multi-geometry Sentinel-1 interferometric synthetic aperture radar (InSAR), revealing widespread and temporally evolving subsidence patterns with rates exceeding 1 cm per year across multiple coastal and inland urban centers. While Jakarta has dominated the subsidence narrative in Indonesia, we find that several other coastal cities, including Cirebon, Pekalongan, Tegal, and Semarang, are sinking two to three times faster, with localized rates approaching 10 cm per year.

To disentangle the dominant drivers of deformation, we applied unsupervised machine-learning spatiotemporal clustering to InSAR time series, guided by geological and land-use information. This analysis reveals nonlinear and spatially heterogeneous subsidence behaviors primarily associated with groundwater extraction in urban, industrial, and agricultural regions, alongside localized deformation linked to natural processes such as volcanism. Finally, we constructed synthetic tide-gauge records at 5-km spacing along the 1,500 km northern coastline by integrating InSAR-derived VLM with satellite altimetry and probabilistic sea-level projections. These virtual gauges show that neglecting land subsidence leads to systematic underestimation of RSL change by more than 90% in some locations and that subsidence will remain the dominant contributor to RSL rise across much of the coastline through 2050.

This work illustrates how geodetic observing systems can fill critical observational gaps in coastal climate research, enabling spatially explicit, process-informed RSL estimates and providing a transferable framework for improving sea-level risk assessments in vulnerable, data-sparse regions worldwide.

How to cite: Ohenhen, L.: Resolving land subsidence contribution to present and future relative sea level change using satellite geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8826, https://doi.org/10.5194/egusphere-egu26-8826, 2026.

Abstract:

Climate change has been proven to exacerbate the ongoing deformations of the Earth's surface in Germany. Also, human activities such as mining, fluid extraction, and reservoir-induced seismicity cause local surface deformations. Therefore, long-term forecasts of Earth's surface movements are needed for infrastructure planning, hazard mitigation, and the sustainable management of natural resources in Germany. By applying Machine Learning (ML) and statistical analyses, we develop scientific scenarios of climate change to forecast surface movements in Germany over the next two decades. Together with Global Navigation Satellite Systems (GNSS), data from five interdisciplinary fields, including the Sun and Moon ephemerides, polar motions, surface loadings, gravity variations, and meteorology, are utilized as features for training ML-based forecast models. Our results indicate that the accuracy of regression ML models reaches millimeter levels, and the decadal forecast models produce fewer than 2% extreme values in the total predictions per year. Based on climate change scenarios, the findings reveal that the average intra-plate motions in Germany will accelerate from ~1.2 mm/yr to ~1.5mm/yr over the next two decades. The annual variations across the 346 GNSS monitoring stations are predicted to increase from 4.7mm to 5.1mm. Surface deformations will be more severe in the southeastern regions and river basins such as the Elbe, Weser, Ems, and Rhine. Significant extensions are expected in the Eifel volcanic region, while notable compressions may occur along the Upper Rhine Graben and the Saxony region in the next twenty years. Additionally, experimental functions showing the statistical distribution of Earth's surface deformation trends in Germany over the next two decades have been proposed. Potentially, the methodology in this study can also be adapted to forecast surface movements related to climate change in polar regions.

Keywords:

Climate change, Surface deformation, Movement forecast, Machine learning, GNSS

How to cite: Le, N., Kłos, A. K., Pham, T. T. T., Luong, T. T., Nguyen, C., and Thomas, M.: Scientific Scenarios of Climate Change for Decadal Forecasts of Earth’s Surface Movements in Germany , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9263, https://doi.org/10.5194/egusphere-egu26-9263, 2026.

Permanent stations of the Global Positioning System (GPS) enable the registration of elastic deformations of the Earth’s surface that occur in response to variations in hydrological mass loads over continental areas. Analysis of long-term changes in displacements observed by a set of GPS permanent stations allows for the identification of deformations induced by long-term changes of the Terrestrial Water Storage (TWS). Densely distributed GPS stations provide adequate spatial coverage for regional scale analysis and their exact spatio-temporal analysis. We use a set of vertical displacements for the period 2010-2020 observed by 493 GPS permanent stations situated in Poland and neighboring regions, whose observations were processed by the Nevada Geodetic Laboratory (NGL). 213 of these stations exhibit more than 80% of temporal coverage with Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On satellite missions. We use these vertical displacements and invert them using elastic Earth theory and load Love numbers to infer trends of TWS in Poland. The obtained results were compared with independent estimates of TWS trends derived from the GRACE and GRACE Follow-On missions, and other external datasets. The analysis demonstrates that GPS-observed vertical displacements provide a reliable source of information for the assessment of TWS trends in Poland.

How to cite: Kłos, K., Klos, A., and Lenczuk, A.: A study of the potential for using trends of GPS displacements to determine TWS trends in Poland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9761, https://doi.org/10.5194/egusphere-egu26-9761, 2026.

Under the assumption that a warming climate leads to an intensification of the global water cycle, it is hypothesized that also the occurrence frequency and severity of extreme events such as droughts and floods will increase in the upcoming decades. GRACE/-FO observations of terrestrial water storage (TWS) have been used in the past to identify and analyse extreme events both on a global and regional scale. However, these analyses are restricted by the limited spatial and temporal resolution of current satellite gravimetry observations. Especially, flooding events tend to occur very locally and with short temporal (sub-monthly) extent, thus capturing them is challenging. Future satellite gravimetry missions, particularly the double-pair constellation MAGIC, are expected to significantly enhance the spatial and temporal resolution. In this study, we globally investigate the benefit MAGIC can achieve to detect wet extreme events using long-term (50 years) end-to-end simulations of GRACE-C and MAGIC.

The simulation environment is based on the acceleration approach and considers tidal and non-tidal background model errors as well as instrument noise of the acceleration and ranging instruments following the current MAGIC mission design studies. As input and reference, we use the daily output of a climate model (GFDL-CM4) from the CMIP6 archive that has been identified as a realistic representation of water storage evolution in previous studies. To explore the improved temporal and spatial resolution expected from the MAGIC constellation, we (i) compare extreme values derived from 5-daily gravity field simulations to those from monthly fields, and (ii) show how the weaker spatial filtering required for MAGIC has a positive influence on the detectability of extremes.

For the analysis two different approaches are exploited: One method focuses solely on the stochastic characteristics of the time series in terms of extreme value theory, evaluating the magnitude-frequency relationship of large TWS values by calculating expected return levels of wet extremes. The other approach builds on the fact that a 50-years simulation time series allows to derive statistically meaningful conclusions from directly comparing reference and simulation output on a time series level. We evaluate the time of occurrence of wet extremes on the basis of classification scores assessing correctly and incorrectly identified extreme events.

How to cite: Middendorf, K., Jensen, L., Schlaak, M., Haas, J., Dobslaw, H., Pail, R., Güntner, A., and Eicker, A.: Benefits of future satellite gravimetry missions for characterizing extreme wet events in terrestrial water storage, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10722, https://doi.org/10.5194/egusphere-egu26-10722, 2026.

Variations in sea level are a globally comprehensively measurable indicator of the effect of climate change on the Earth system. Satellite geodesy provides data with global coverage to analyze sea level changes in space and time, but also to investigate the individual contributions to sea level from the subsystems oceans, continental hydrology, glaciers, ice sheets, and the solid Earth. Particularly valuable for this purpose are time-variable satellite gravity, realized by the GRACE and GRACE-FO missions, and satellite altimetry over the oceans, realized, e.g., by the Jason-1/-2/-3 and Sentinel-6 reference missions. However, previous studies show that the uncertainty of the estimated Antarctic Ice Sheet’s contribution to sea level remains large, primarily due to errors in the glacial isostatic adjustment (GIA) correction. We use a global fingerprint inversion method that evaluates GRACE and ocean altimetry data in a globally consistent framework and enables the quantification of individual contributions to sea level on a monthly basis on global grids. The inversion is additionally supplemented by observations from Argo floats. The parametrization of the contributions from steric effects, ice sheets, glaciers, hydrology, and GIA are realized by time-invariant sea-level fingerprints obtained from a priori information. This includes, e.g., the locations of mass changes or statistically obtained information from geophysical model simulations. In a methodological advancement of the inversion method, we have implemented a new parametrization of the ice mass changes (IMC) of the Antarctic ice sheet. Previously, IMC and corresponding sea level change has been estimated only on basin level for 27 large ice catchment areas, so-called drainage basins. However, this coarse parametrization of IMC prevents the inversion method from better resolving errors in the GIA correction in upcoming inversion implementations. We have therefore introduced a high-resolution parametrization based on individual grid points with a resolution of up to 50 km, resulting in up to 4755 Antarctic mass balance parameters to be estimated in a globally consistent way. In order to solve this inverse problem, we introduced altimetry over ice sheets as an additional observation at a 10 km spatial and a monthly temporal resolution. We present and discuss results from different variants of parametrization of IMC and different variants of implementation of ice altimetry observations. This methodological advancement presented here is a necessary step towards minimizing GIA-related errors when determining the sea level budget utilizing this global framework in the future.

How to cite: Willen, M. O., Uebbing, B., Horwath, M., and Kusche, J.: A global inversion for sea-level contributions from satellite data: towards improving Antarctica's representation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10826, https://doi.org/10.5194/egusphere-egu26-10826, 2026.

Accurate estimation of vertical land motion in Antarctica is crucial for understanding glacial isostatic adjustment (GIA), ice mass change, and sea-level rise. However, Global Navigation Satellite System (GNSS) position time series are affected by non-tidal loading (NTL), which can obscure geophysical signals and bias trend estimates. In this study, we evaluate the performance of 11 NTL model combinations from EOST (École & Observatoire des Sciences de la Terre, Strasbourg) and ESMGFZ (Earth System Modelling Group, GFZ Potsdam) in correcting vertical GNSS time series at three East Antarctic stations in Dronning Maud Land. We analyse five GNSS solutions processed with different strategies, including precise point positioning (PPP), double-difference (DD) network solutions, and a combined product.

Our results show that NTL corrections improve time series quality in PPP-based solutions, reducing root mean square (RMS), coloured noise, and seasonal amplitudes by more than 20 % at some sites. In contrast, network-based and combined solutions exhibit limited improvements, and in some cases, corrections introduced additional variability. Among loading components, non-tidal atmospheric loading (NTAL) consistently produces the largest reductions, while additional non-tidal oceanic (NTOL) and hydrological loading (HYDL) contributions are beneficial mainly in specific GFZ model combinations applied to PPP datasets.

Our findings demonstrate that both GNSS processing strategy and NTL model choice can affect inferred vertical trends, and in some cases even change their sign. Our evaluation provides a regional assessment of widely used NTL products under Antarctic conditions, with direct implications for GIA modelling and reference frame realisation, and supports the development of more robust correction strategies for future Antarctic GNSS studies.

How to cite: Schulz, A., Ejigu, Y. G., Näränen, J., and Nordman, M.: Impact of non-tidal loading corrections and processing strategy on Antarctic GNSS vertical time series, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10838, https://doi.org/10.5194/egusphere-egu26-10838, 2026.

Our analysis presents 10-day water mass solutions estimated from both GRACE and GRACE-FO KBR Range (KBRR) residuals for continental hydrology using GINS software developed by the CNES/GRGS group.  The inter-satellite velocity residuals have been converted into along-track differences of gravity potential using the energy balance approach. Maps of Equivalent Water Height (EWH) are obtained by inversion of these potential differences onto juxtaposed surface elements over the region of interest or time coefficients of designed orthogonal Slepian functions. This latter band-limited representation offers the advantage of reducing  drastically the number of parameters to be fitted and the computation time. We also used another type of orthogonal basis functions, as well as decomposition using anisotropic wavelets. These functions require larger computing resources but have the advantage of being adapted to the shape of the studied watersheds for improving hydrology variation survey locally. All of these regional solutions are compared to spherical harmonics and mascons series of existing Level-2 solutions for validation. The patterns shown in the proposed regional solutions reveal dominant seasonal cycles of water mass in the large tropical basins (e.g. Amazon,  Nil and Congo), as well as extreme events such as floods and droughts.

How to cite: Seoane, L., Ramillien, G., and Darrozes, J.: Multi-year regional water mass solutions by inversion of hydrology-related GRACE(-FO) KBRR residuals, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10903, https://doi.org/10.5194/egusphere-egu26-10903, 2026.

The Gravity Recovery and Climate Experiment (GRACE) and its successor GRACE-FO provide unique observations of Earth’s time-variable gravity field, enabling direct monitoring of mass redistribution expressed as equivalent water height (EWH). While gridded Level-2B products are widely used across hydrology, glaciology, and solid-Earth studies, uncertainty information remains fragmented or inaccessible to end users. In practice, this has led to the widespread use of empirical or ad hoc uncertainty estimates, limiting data assimilation and other geophysical applications that require spatially and temporally resolved observational error information.

We present TUD-L2B-EWH_UNC-GRACE, a globally gridded Level-2B GRACE(-FO) EWH data product that provides a comprehensive and transparent characterisation of uncertainty alongside the mass anomaly fields. Unlike conventional approaches that rely on propagation of full normal matrices or impose assumptions on error correlations, TUD-L2B-EWH_UNC combines ensemble statistics from multiple independently processed Level-2 solutions to quantify pre-processing uncertainties. These include contributions from ocean tide model differences, parametrisation strategies, and uncertainty in the Atmosphere and Ocean De-aliasing (AOD1B) background model.

Post-processing uncertainties associated with filtering, leakage, and Glacial Isostatic Adjustment (GIA) are quantified separately. Filtering-related uncertainty is evaluated using a known-pair approach, while GIA uncertainty is assessed using an ensemble of 56 published GIA models. Error fields are provided for a suite of anisotropic filtering strategies (DDK(2–7)), enabling systematic assessment of filtering choices, leakage effects, and model dependence on the total uncertainty budget.

TUD-L2B-EWH_UNC is the first Level-2B EWH dataset to deliver end-to-end, spatially and temporally resolved uncertainty fields in a user-ready gridded format. This design supports consistent uncertainty handling across hydrological, glaciological, and solid-Earth applications. Ancillary tidal corrections and climatological fits of signal and leakage-related errors are distributed separately through the companion products TUD-L2B-EWH_CLIM-GRACE and TUD-L2B-EWH_CLIM_LEAKAGE-GRACE. All datasets are publicly available (DOI: doi.org/10.4121/4fc748e8-01c7-4f06-87da-653937b078f7) via the TU Delft GRACE Portal (https://grace-cube.lr.tudelft.nl/).

How to cite: Cuadrat-Grzybowski, M. and de Teixeira da Encarnacao, J. G.: TUD-L2B-EWH_UNC: A Monthly Global Level-2B GRACE(-FO) EWH Uncertainty Product, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11806, https://doi.org/10.5194/egusphere-egu26-11806, 2026.

How to cite: Nitschke, A., Kusche, J., and Hendricks Franssen, H.-J.: Improving the representation of water, energy and carbon cycles in land surface modelling: Assimilation of MAGIC TWSA data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12466, https://doi.org/10.5194/egusphere-egu26-12466, 2026.

The Svalbard Archipelago, located in the Arctic region of Norway, is extremely vulnerable to the climate change. With a current increase of 3 at 5°C in average air temperature and a change in precipitation with an increasing proportion of rain, certain negative consequences for the environment and ecosystem are inevitable. One of the most obvious signs of climate change in this region is the melting of ice, which is causing the Earth’s crust to deform. But there are other consequences, such as the loss of sea ice cover, changes in how sediment is transported and also changes in biodiversity.

These phenomena are widely studied in this region. For example, deformation of the Earth’s crust is determined using 3D positioning data acquired by GNSS across Svalbard, particularly  in Ny-Alesund. Since 2000, daily positioning time series show a strong upward component, with an average vertical velocity of between 8 to 13 mm/yr. This velocity is the Earth’s response  to various episodes of glaciation and deglaciation in the past like the last glacial maximum or the Little Ice Age, and to the current melting of ice. This current melting has also been  studied a lot at Ny-Alesund station, where glaciers are monitored to measure changes in ice height from one year to the next and calculate the glacier’s surface mass balance. This is the case for the Austre Lovenbreen, for which data has been available since 2007, showing record melting over the last ten years. The same is true for the study of the prodeltas evolution since 2009, which shows a stabilisation of almost all prodeltas since 2016.

All these phenomena are largely studied separately, but our analysis consists of interpreting all this data in order to study the possible correlation between these observations which share the same cause: climate change. In our study, we ask how we can link measurements taken at the glacier or in the underwater sediment, along with space geodesy data, to better understand the ongoing geophysical processes that mark the transition between a glacial environment and paraglacial environment.

How to cite: Tafflet, A., Nicolas, J., Baltzer, A., Verdun, J., Tolle, F., Bernard, E., and Friedt, J.-M.: Study of changes induced by global warming in Svalbard based on spatial geodetic data and in situ geophysical measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12707, https://doi.org/10.5194/egusphere-egu26-12707, 2026.

The Gravity Recovery and Climate Experiment (GRACE) and its follow-on mission (GRACE-FO) have been providing spaceborne observations of terrestrial water storage (TWS) changes since 2002. These observations help to understand how water fluxes change in an intensifying water cycle at watershed scales. However, the accuracy of the derived TWS anomalies depends on the choice of spatial and spectral filtering methods, which can attenuate their amplitude.

In this poster, we present our filter-free inversion scheme that estimates TWS anomalies at watershed scales from Level-2 Stokes coefficients together with their associated full error covariance matrices. We apply the scheme to the watersheds in the Greater Horn of Africa and compare the obtained TWS anomalies with the accumulated watershed-wide precipitation and evapotranspiration fluxes from the ERA5 atmospheric reanalysis, and the accumulated river discharge from GLOFAS and GEOGLOWS products. We further assess the consistency between the temporal derivatives of TWS anomalies and the corresponding water fluxes. Additionally, we quantify mass deficits and surpluses in TWS anomalies and investigate the relative contributions of atmospheric net flux (i.e., precipitation minus evapotranspiration) and river discharge to the magnitude of TWS anomalies during drought and flood events.

How to cite: Karimi, S., Rietbroek, R., Penning de Vries, M., and van der Tol, C.: Quantifying mass signatures of drought and flood events using water fluxes and terrestrial water storage anomalies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12852, https://doi.org/10.5194/egusphere-egu26-12852, 2026.

Antarctica plays a central role in Earth's global climate system and stores most of the planet's freshwater. However, due to the continent's remoteness and extreme conditions, reliable in situ observations of snow accumulation remain rare. This gap in measurements makes it difficult to constrain ice sheet models and accurately project Antarctica's contribution to global sea level rise. In particular, regions such as the Totten Glacier in East Antarctica are of interest due to the significant mass loss since the 1990s, dominated by changes in coastal ice dynamics. In the context of Antarctica, GNSS Interferometric Reflectometry (GNSS-IR) presents an efficient and sustainable approach to monitor changes in snow accumulation with the potential to offer insights into regional surface mass balance models.

This contribution investigates a unique in situ dataset of six GNSS stations deployed on the Totten Glacier, operated seasonally between November 2016 and January 2019. These stations were originally designed to track ice motion, but they also capture reflections from the snow surface. By applying GNSS-IR, time series of snow accumulation are generated – once with the traditional retrieval approach using the gnssrefl software, and once by testing a novel machine learning-based retrieval framework. The derived snow accumulation time series are cross-referenced with outputs from regional surface mass balance models. The results provide insights into the spatio-temporal patterns of snow accumulation over the Totten Glacier and showcase the potential of GNSS-IR for environmental sensing.

How to cite: Crocetti, L., Watson, C., Schartner, M., and King, M.: Snow Accumulation Monitoring using GNSS-Interferometric Reflectometry for Antarctica, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15089, https://doi.org/10.5194/egusphere-egu26-15089, 2026.

Satellite gravimetry has revolutionized the observation of shifts in terrestrial water storage (TWS) in reponse to climate and human activities. Robust detection and attribution of these changes remain a challenge because TWS exhibits strong seasonal variability and is traditionally observed at coarse spatial and temporal resolution. Recent studies have shown that direct regression of Level-1B observations (inter-satellite range data) from the Gravity Recovery and Climate Experiment (GRACE) and its Follow-On mission (GRACE-FO) can substantially improve effective spatial resolution of regression terms, compared to popular monthly mascon products. Applying this framework, we demonstrate that stacked Level-1B regression yields spatially refined estimates of both long-term TWS trends and seasonal amplitude, improving the ability to identify regions where human land and water use alter local freshwater availability. For trend analysis, the enhanced resolution strengthens attribution of storage change to anthropogenic drivers such as irrigation, groundwater extraction, reservoir operations, and land-use change at sub-basin scales. For seasonal characterization, we show that assuming simplified representations of the annual cycle, such as stationary, symmetric, or unimodal seasonality, can enable robust recovery of mean annual TWS amplitude with substantially reduced signal attenuation and leakage. Such refinements are particularly important for applications that depend on accurate annual water budgets, including water-balance-based evapotranspiration estimation and assessments of interannual hydroclimatic variability. The spatial scale at which GRACE satellites can independently observe water resources will continue to improve as additional years of measurements become available.

How to cite: O'Neill, M. M., Rodell, M., and Loomis, B.: Spatially refined global terrestrial water storage trends and annual cycles from GRACE and GRACE-FO, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16019, https://doi.org/10.5194/egusphere-egu26-16019, 2026.

The Gravity Recovery And Climate Experiment (GRACE) and its follow-on mission, GRACE-FO, have observed global mass changes and transports, expressed as total water storage anomalies (TWSA), for over two decades. However, for climate change attribution and other applications, multi-decadal TWSA time series are required. This need has prompted several studies on reconstructing TWSA using regression or machine learning techniques, aided by predictor variables such as rainfall and sea surface temperature. However, the training period is limited to a couple of years, making it hard to capture interannual signals accurately. Furthermore, learned relationships between climate variables and water storage cannot be transferred straightforwardly to the past. To overcome the limitation and provide a more long-term, consistent dataset, we derive a preliminary reconstruction and combine it with large-scale time-variable pre-GRACE gravity information from geodetic satellite laser ranging (SLR) and Doppler Orbitography by Radiopositioning Integrated on Satellite (DORIS) tracking from Löcher et al. (2025). We reconstruct GRACE-like TWSA for the global land, excluding Greenland and Antarctica, from 1984 onward. We find that the seasonal cycle of our new reconstruction is consistent with that of previously published purely climate-data-based reconstructions. Moreover, in many regions, TWSA trends were markedly different in the pre-GRACE timeframe, and we thus suggest caution when interpolating GRACE-derived trends.

How to cite: Hacker, C., Gutknecht, B. D., Löcher, A., and Kusche, J.: Reconstructing terrestrial water storage anomalies based on climate data and pre-GRACE satellite observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16439, https://doi.org/10.5194/egusphere-egu26-16439, 2026.

In existing GNSS-based terrestrial water storage (TWS) inversion studies, the PREM model is commonly adopted, and crustal structural heterogeneity is often neglected. Here, we conduct a comprehensive assessment of how different Earth models affect inversion results using both checkerboard-model experiments and continuous smooth-model experiments. The results show that, under realistic hydrological loading conditions within the study region (100°E–115°E, 25°N–40°N), inversion differences among global 1-D reference Earth models are below 2%, whereas the differences between global 1-D reference models and regional crustal models are ~11%; meanwhile, discrepancies between the two regional crustal models remain below 4%. Application to observed GNSS coordinate time series in Yunnan indicates that the spatial pattern of the annual equivalent water height (EWH) amplitude derived from GNSS is broadly consistent with that from the GLDAS hydrological model; however, the choice of Earth model can still substantially alter the magnitude of the inferred amplitude and its spatial distribution. Correlation analyses further suggest that Earth-model dependence is weak for large-scale inversions, but becomes non-negligible at smaller spatial scales. For a representative small-scale subregion (101.75°E–102°E, 22.75°N–23°N), we therefore recommend using the AK135F model to construct Green’s functions. Overall, our findings demonstrate that Earth-model selection is a key source of uncertainty in GNSS-based TWS inversion, and provide practical guidance for choosing appropriate Earth models to improve inversion accuracy.

How to cite: He, J. and Li, Z.: Impact of Earth Model Selection on Terrestrial Water Storage Inversion from GNSS Vertical Displacements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17088, https://doi.org/10.5194/egusphere-egu26-17088, 2026.

Monitoring essential climate variables such as Sea level rise, Earth’s Energy Imbalance, and ice-mass changes relies critically on space-geodetic observations of surface deformation and variations of the gravity field.
In particular, satellite geodesy provides decades-long, globally consistent records that are fundamental for quantifying climate-driven surface mass redistribution. However, these observations integrate both mass changes from the oceans, atmosphere, cryosphere and continental hydrology and the associated solid Earth response. Isolating climate variables from geodetic data therefore requires models that reflect the solid Earth response across timescales relevant to contemporary variability.
Yet, a critical assumption underlies much of current space-geodetic standard processing: the solid Earth response to surface mass variations is treated as purely elastic, i.e. instantaneous and fully recoverable. However, there is a growing body of evidence from laboratory rock mechanics experiments and geophysical observations suggesting that the Earth’s mantle exhibits a time-dependent, recoverable anelastic response across intermediate timescales  that could significantly affect geodetic at decadal to centennial timescales.
Here, we exploit several decades of Satellite Laser Ranging (SLR) observations towards passive spherical satellites to constrain key parameters governing the time-dependent mantle anelasticity. Owing to long-term measurements and sensitivity to low-degree gravity field variations, including solid Earth tides (C20, C30) and the pole tide (C21/S21), SLR observations are particularly well suited to probing deep Earth mantle rheology over decadal timescales.
We combine analytical orbit perturbation theory with the Hill-Clohessy-Wiltshire equations to quantify the sensitivity of the SLR observables to rheology and to choose an optimal parametrization. We then numerically estimate the solid Earth transient rheological properties from the SLR time series using an anelasticity framework consistent with seismic attenuation theory. Our results are compared with independent rheological constraints and yield a new set of frequency-dependent Love numbers that capture the Earth’s mantle transient rheology across decadal timescales.
We further show that accounting for this  transient rheology by incorporating the corresponding frequency-dependent Love numbers into the modeling of solid Earth tides, pole tide and surface loading-induced deformation, introduces systematic differences in climate-relevant geodetic time-series, including  satellite altimetry sea level rise estimates and ocean mass trends derived from satellite gravimetry.
More broadly, our results show that as space geodetic records become longer, data processing cannot rely solely on an  elastic solid Earth assumption. Instead, it must account for solid Earth transient rheology and the fact that geodetic observables will increasingly depend on the cumulative loading history, strengthening the need for interdisciplinary geodetic, geophysical and climate studies.

How to cite: Rousselet, M., Couhert, A., Chanard, K., Exertier, P., and Fleitout, L.: Constraining transient solid Earth rheology using satellite orbit perturbations to assess the dynamics of climate change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18067, https://doi.org/10.5194/egusphere-egu26-18067, 2026.

Since 1992, surface elevation change estimates of the Antarctic Ice Sheet (AIS) have been derived from satellite radar altimetry. However, large uncertainties remain due to local topography and the time-variable signal penetration into snow and firn. The unprecedented accuracy of measurements from the ICESat-2 satellite laser altimetry mission, launched in 2018, now enables inter-comparison with radar altimetry results. The primary goal of this study is to improve understanding of the uncertainties in AIS volume and mass balance estimates by quantifying how results from ICESat-2 and the CryoSat-2 radar altimetry mission diverge under different processing regimes. To do so, we analyse coincident ICESat-2 and CryoSat-2 measurements over the 6.9 million km² area of the relatively flat and large AIS interior, where topography-related errors are small. We apply a suite of state-of-the-art correction methods to the CryoSat-2 measurements, including multiple retracking algorithms and empirical corrections for the time-variable surface and volume scattering of the radar signal. From April 2019 to October 2024, ICESat-2 observations show a thickening of 97 ± 4 km³ yr⁻¹, coincident with excess snowfall in this period. CryoSat-2 solutions indicate systematically lower thickening rates than ICESat-2. The smallest bias (0.6 ± 1.0 cm yr⁻¹ or 42 km³ yr⁻¹) between the results from the two missions is found when using the AWI-ICENet1 convolutional neural network retracker. One of our hypotheses is that the systematic radar-laser differences might be due to residual errors related to the time-variable radar penetration, particularly affected by the heavy snowfall events in recent years. While further work is needed to test this hypothesis, our study demonstrates both the challenges of resolving subtle, long-term surface mass balance trends using radar altimetry and the value of joint laser-radar analyses for improving AIS volume and mass balance estimates.

How to cite: Kappelsberger, M. T., Nilsson, J., Horwath, M., Helm, V., Gardner, A. S., and Willen, M. O.: Uncertainties in Antarctic elevation change estimates by comparing radar and laser altimetry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18146, https://doi.org/10.5194/egusphere-egu26-18146, 2026.

The SING project aims to evaluate the added value of the NGGM and MAGIC missions for scientific applications and operational services in hydrology, ocean sciences, glaciology, climate sciences, solid earth sciences, and geodesy. Using a closed-loop simulator with a comprehensive description of instrumental, ocean tide, dealiasing and toning errors, synthetic observations of the gravity field have been generated to assess the observability of mass changes occurring in the atmosphere, ocean, hydrosphere, cryosphere, and solid earth for different mission configurations, including GRACE-C-like (single polar pair), NGGM (single inclined pair), and MAGIC (double pair). 

The synthetic gravity observations have first been used to assess the closure of the sea level budget. With historical GRACE, altimetry, and Argo data, global sea level budget closure is achieved with an accuracy of 0.3–0.4 mm/yr (2003–2015). Using VADER-filtered simulations, all three configurations contribute <0.1 mm/yr to the global mean sea level error. NGGM and MAGIC maintain this accuracy even without filtering, unlike GRACE-C. At regional scales, NGGM and MAGIC notably improve significantly the sea level budget closure, especially at seasonal and interannual timescales, though gains for decadal trends remain modest. 

The synthetic gravity observations were also used to assess the closure of the global energy budget. Historical gravimetry, altimetry, and Argo data yield global mean ocean heat uptake (GOHU) accuracy of 0.2–0.3 W/m² (2003-2015). With VADER-filtered simulations, GRACE-C-like missions contribute up to 0.19 W/m² uncertainty, while NGGM and MAGIC improve this by 30–40%, achieving ~0.12–0.13 W/m² accuracy. They also enhance the stability and temporal consistency of GOHU retrievals. Regionally, NGGM and MAGIC outperform GRACE-C by up to 80% in recovering ocean heat content changes at mid-latitudes (30–60° N/S). Slightly better results are obtained with NGGM due to the use of mission error covariance information in the VADER filter. NGGM and MAGIC recover mean and temporal variations in ocean heat uptake at regional scales with up to 50% higher accuracy than GRACE-C.
The NGGM and MAGIC missions will substantially enhance the accuracy, spatial and temporal resolution of gravity-based observations of sea level changes and its drivers. These improvements strengthen global climate assessments, support the evaluation of mitigation policies, and improve climate model validation. In particular, sustained and redundant monitoring of ocean heat uptake would provide an early and robust indicator of changes in radiative forcing, preceding detectable stabilization of global temperatures by several decades. Improved characterization of regional heat-uptake pathways also enhances projections of sea level rise, marine heat extremes, and ocean circulation changes, supporting climate risk management across coastal, marine, and ecosystem applications.

How to cite: Ferrari, R., Pfeffer, J., Bouih, M., Meyssignac, B., Blazquez, A., and Daras, I.: Impact of NGGM and MAGIC on Sea Level and Energy Budgets Closure, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18337, https://doi.org/10.5194/egusphere-egu26-18337, 2026.

The closure of the Sea Level Budget (SLB) is a key challenge for modern physical oceanography. First, it is essential that we ensure the proper identification and quantification of each significant contributor to sea level change through this closure. Second, it provides an efficient means to closely monitor and cross-validate the performance of intricate global observation systems, such as the satellite altimetry constellation, satellite gravimetry missions (GRACE/GRACE-FO), and the Argo in-situ network. Third, this closure reveals to be a beneficial approach for assessing how well the observed climate variables, such as sea level, barystatic sea level, temperature and salinity, land ice melt, and changes in land water storage, comply with conservation laws, in particular those related to mass and energy.

In this presentation, we will discuss the state of knowledge of global mean and regional sea level budget with up-to-date observations, encompassing 1) an up-to-date assessment of the budget components and residuals, along with their corresponding uncertainties, spanning from 1993 to 2023 in global mean and throughout the GRACE and Argo era for spatial variations; 2) the identification of the periods and areas where the budget is not closed, i.e. where the residuals are significant; 3) advancements in the analysis and understanding of the spatial patterns of the budget residuals. 

To investigate the sea level budget (SLB) misclosure, we developed an objective solution that closes the SLB globally. This approach is based on an inverse method that optimally combines the contributions to sea level, weighted by their estimated instrumental uncertainties, and draws from publications such as those by Rodell et al. (2015) and L’Ecuyer et al. (2015).

This objective method allows us to precisely identify the dates when the SLB misclosure falls outside the uncertainty estimates, as well as the contributor most likely responsible for the discrepancy. The results of this analysis will be detailed during the presentation.

A focus will be made on the North Atlantic Ocean where the residuals are significantly high. We investigate the potential errors causing non-closure in each of the components (e.g., in situ data sampling for the thermosteric component, geocenter correction in the gravimetric data processing) as well as potential inconsistencies in their processing that may impact large-scale patterns (e.g., centre of reference and atmosphere corrections). 

This work is performed within the framework of the Sea Level Budget Closure Climate Change Initiative (SLBC_cci+) programme of the European Space Agency (https://climate.esa.int/en/projects/sea-level-budget-closure/). This project was initiated by the International Space Science Institute Workshop on Integrative Study of Sea Level Budget (https://www.issibern.ch/workshops/sealevelbudget/).

How to cite: Bouih, M., Fraudeau, R., Pfeffer, J., Ferrari, R., Ablain, M., Cazenave, A., Meyssignac, B., Blazquez, A., Horwath, M., Bamber, J., Bonaduce, A., Raj, R., Leroux, S., Kolodziejczyk, N., Llovel, W., Spada, G., Storto, A., Yang, C., and Oulhen, E. and the ESA SLBC CCI+ team: How is the global and regional sea level budget closed from the latest observations? , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18774, https://doi.org/10.5194/egusphere-egu26-18774, 2026.

The primary indicators of relative sea-level change along the coasts of Antarctica are the uplifted paleoshorelines, which are documented with geomorphological and geochronological studies, particularly from the Antarctic Peninsula. Some of the most prominent examples are found along the shores of Marguerite Bay, situated in the central part of the Antarctic Peninsula. Here, we present that the shorelines of Calmette Bay, located within the research area, have experienced approximately 40 m of uplift over the past 7500 years. This study aims to quantify the amount of ice mass loss required to produce such a rapid uplift and to assess the magnitude of climate change necessary to drive this degree of ice mass reduction. In addition, our goal is to constrain the mantle rheology and viscosity conditions required to produce the observed crustal response in the region. Our approach integrates various Antarctic ice-deglaciation scenarios with crustal viscosity models. We employ the numerical code SELEN⁴ to compute the sea-level equation and generate theoretical uplift/subsidence curves. We compare our results with geological data to assess alternative ice deglaciation histories and to constrain the mantle-rheology parameters that most effectively reproduce the observed uplift pattern.

How to cite: Güven, A. and Yıldırım, C.: Glacio-isostatic Adjustment (GIA) in Marguerite Bay, Antarctic Peninsula: inferences from uplifted Holocene paleoshorelines, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-839, https://doi.org/10.5194/egusphere-egu26-839, 2026.

The hypothesis of the ISVOLC project is that retreat of Icelandic glaciers since the end of the 19th Century has the potential to impact both volcanic and seismic activity. As volcanic activity increased significantly during (and in the <2kyr after) the late Pleistocene deglaciation, it is expected that present day deglaciation will once again effect volcanic activity in Iceland. The unloading of glaciers and subsequent rebound response of the Earth can significantly alter the state of stress in the crust and mantle. Within the ISVOLC project (https://isvolc.is) we have developed a new generation of Finite Element Glacial Isostatic Adjustment (GIA) models, using the COMSOL Multiphysics software package, which employ spaciotemporal estimates of glacier mass balance. Utilizing this new detailed ice history, we simulate GIA numerically and, once best fit earth parameters are found by utilizing InSAR and GNSS measurements, produce revised estimates for stress changes in the crust and mantle. From these we can calculate mantle decompression melting increases and shallow crustal stressing which may already be affecting volcanism and seismicity. We find that rates of total magma production beneath Iceland are enhanced by up to a factor of ~3 due to the glacier retreat induced decompression melting. However, it is highly uncertain when this additional magma will reach the surface and in what volumes. Stress changes around magma bodies at shallow level in the crust can bring such magma bodies closer to or further away from failure, depending on their geometry. Our new models predict stressing rates in the shallow crust that are comparable to those from tectonic extension for volcanic systems, seismic zones, and fissure swarms that are near or underneath Vatnajökull (Bardarbunga, Grímsvötn, northeastern Volcanic Zone, south Northern Volcanic Zone), with a unique pattern for each system. Glacially induced stressing in these areas may significantly shorten the timeline to seismic, diking, or eruptive events and alter the preferred orientations of dike propagation. Stressing rates from glacial mass loss are an order of magnitude smaller for systems beneath smaller glaciers and those not beneath ice (e.g. Askja, Katla, South Iceland Seismic Zone, Tjornes Fracture Zone), but still significant enough to consider when assessing hazard. Efforts in further improving the GIA modeling include effects of more realistic non-linear mantle rheology leading overall to somewhat higher viscosity estimates and more subdued GIA response in the far-field, as well as increases in the rate of magma production predicted by our models. Near-future work will involve the projection of glacial unloading and the subsequent earth response to evaluate effects on long-term hazards.

How to cite: Givens, T., Bellagamba, G., Parks, M., Schmidt, P., Sigmundsson, F., Geirssson, H., O´Hara, C., Sturkell, E., Ófeigsson, B., Drouin, V., Frídriksdóttir, H., Greiner, S., Vallson, G., Halldórsson, H., Magnússon, E., Pálsson, F., and Hreinsdóttir, S.: ISVOLC: Deglaciation and GIA Affecting Crustal and Mantle Stresses in Iceland. Much More Magma?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1014, https://doi.org/10.5194/egusphere-egu26-1014, 2026.

Vertical land motion in the Great Lakes Basin (GLB) arises from the combined effects of ongoing Glacial Isostatic Adjustment (GIA) and shorter-term environmental and hydrological loadings. Because the present-day GIA hinge line crosses the region, even small errors in separating long-term uplift from elastic responses can strongly bias geophysical interpretations. Over the past two decades, the GLB has experienced pronounced lake-level fluctuations. An analysis of GRACE/FO data indicates minimal Total Water Storage (TWS) changes across the GLB during 2002-2012, a period during which lake levels were relatively stable and vertical motions should therefore reflect GIA alone. In contrast, from 2012 to 2019 lake levels rose to record highs, and since 2020 they have been falling at a comparable rate. The area is densely instrumented with continuous GNSS stations, providing an exceptional opportunity to investigate how long-term GIA and short-term hydrological forcing interact. Our goal is to develop a robust, precise and accurate estimate of the GIA signal so that we can accurately remove GIA from observations and constrain surface/groundwater storage changes.

We compared the predictions of many GIA models with the pre-2012 observations, which should reflect the GIA signal alone, but none of the existing models adequately reproduce the observed data. Despite differences in viscosity structure or ice history, every model produces the same systematic bias: the hinge line (zero uplift) is positioned too far south. However, the shape of the modelled profiles matches the GNSS curvature extremely well.  Therefore, we developed a spatial optimization framework to minimize geometric misalignments between GIA model predictions and GNSS vertical velocities across the Great Lakes (2002–2012.5). Seventy-two GIA realizations based on diverse ice histories (ICE-6G_C, ICE-6G_D, ICE-7G_NA, ANU-ICE, NAICE, etc.) and Earth rheologies were subjected to systematic horizontal translations (via a grid search with limits ranging from ±2° to ±8°), with and without allowing for small planar rotations, yielding 576 model-configuration combinations evaluated using RMS misfit, concordance correlation, and 5-fold cross-validation. The best-fitting models achieve the lowest misfits (approximately 0.40 mm/yr), and highest concordance (ccc > 0.90). The models that fit well give very consistent hinge line predictions across the core of our region but are more variable toward the edges of the model domain.

We introduced a hierarchical set of model ensembles constructed by ranking all 576 optimized configurations by post-alignment RMS and grouping them into four tiers: ELITE (RMS ≤ 0.49 mm/yr), GOOD (≤ 0.59 mm/yr), MEDIUM (≤0.79 mm/yr), and ALL (>0.80 mm/yr). These hybrid fields reveal a systematic progression, with the ELITE and GOOD ensembles capturing the GNSS-derived deformation shape with narrow uncertainty bands, while the MEDIUM and ALL ensembles exhibit progressively larger uncertainties that grow with ensemble size. The mean models of the ELITE and GOOD ensembles are nearly identical and provide the most stable uplift geometry and the smallest GPS-calibrated uncertainties, with representative values below 0.18 mm/yr (ELITE) and 0.26 mm/yr (GOOD) for Michigan, demonstrating that tightly constrained multi-model ensembles can outperform any individual GIA realization.

How to cite: Guerra Neto, H. L. and Freymueller, J.: An Empirical Estimate of GIA-Induced Vertical Motion in the Great Lakes Basin Derived from an Ensemble of GIA Models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1437, https://doi.org/10.5194/egusphere-egu26-1437, 2026.

How to cite: van Calcar, C., Broerse, T., Ioannidi, I., Breithaupt, T., Wallis, D., Willen, M., Riva, R., van der Wal, W., and Govers, R.: Time-dependent rheological behaviour of the solid Earth greatly influence Antarctica's future sea-level contribution., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1883, https://doi.org/10.5194/egusphere-egu26-1883, 2026.

A glacial forebulge is a load-driven bending-related upheaval of the lithosphere outside a glaciated area. As a typical feature of the glacial isostatic adjustment process the forebulge forms contemporaneously to the depression of the lithosphere below the ice sheet. Forebulge development and collapse related to the last glaciation has led to significant topographic changes in the order of several tens of meters in North America and Europe. Furthermore, forebulge behaviour has a significant effect on the evolution of lithospheric stresses, which can induce intraplate earthquakes, even in areas that were not covered by an ice sheet. Therefore, quantifying the present-day position, amplitude and subsidence of the forebulge is crucial for the estimation of future sea-level changes, the evolution of fluvial networks and understanding the distribution of deglaciation seismicity. Though the forebulge of the last glaciation attracted attention over more than one century, quantitative descriptions on the geometry and position of the forebulge are still rare. Key controlling factors for the position, amplitude and dynamic behaviour of the forebulge are the flexural rigidity of the lithosphere, asthenospheric flow processes, as well as ice-sheet geometry and history. Numerical simulations indicate that a higher flexural rigidity of the lithosphere leads to a lower amplitude of the forebulge and a greater distance to the load. Forebulge formation is also supported by the flow of asthenospheric material, which can occur as channel-flow or deep flow. In case of channel-flow, the forebulge shows an outward migration during collapse, whereas deep-flow leads to an inward migration. A non-linear mantle rheology is seen as a reason for stationary forebulge collapse. The height of the glacial forebulge of the last glaciation was in a range of several tens of meters, with a greater height in North America than in Europe due to the larger Laurentide ice sheet. 

How to cite: Brandes, C., Steffen, H., Steffen, R., Li, T., and Wu, P.: Quantifying the forebulge of the last glaciation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2315, https://doi.org/10.5194/egusphere-egu26-2315, 2026.

Owing to vertical land movement (VLM), Norway has long had falling or stable relative sea levels and is yet to feel the impacts of sea-level rise. The danger is that this can foster a false sense of security, where the long-term risks are not understood or ignored.

Results from a recent national assessment show that sea-level rise is starting to push up water levels in some parts of the coast, most notably in Western and Southern Norway. Owing to global warming, Norway is transitioning from a country with on average falling or stable relative sea level, to one with rising relative sea levels. Measured coastal average geocentric (the ocean surface) sea-level rise is 2.3 ± 0.3 mm/yr for the period 1960-2022, i.e., an increase of 14 ± 2 cm over that time.

IPCC AR6 sea-level projections are tailored to the Norwegian coast using the semi-empirical model NKG2016LU to estimate VLM and associated geoid changes. Although the broad pattern of regional VLM is caused by glacial isostatic adjustment, there is evidence of other processes driving changes, especially on local scales. Projections show Norway’s coastal average relative sea-level change for 2100, compared to the period 1995-2014, will range from 0.13 m (likely -0.12 to 0.41 m) for the very low emissions scenario (SSP1-1.9) to 0.46 m (likely 0.21 to 0.79 m) for the very high emissions scenario (SSP5-8.5). A rise between 40% and 70% lower than the projected global average. For scenarios with higher greenhouse gas emissions than SSP1-2.6, a majority of the coast will likely experience relative sea-level rise for 2100.

Sea-level rise will increase flood risk in Norway by pushing up the height of sea level extremes (the combination of tides, storm surges, and waves) which will reach higher and further inland. Sea-level rise will also drive sharp increases in flooding frequency. There are large differences in the timing and extent of flooding frequency changes that partly depend on projected sea level and the regional VLM signal. Western and Southern Norway will experience increases in flooding frequency first.

In summary, careful treatment of VLM and its uncertainties is important for assessing observed sea level and tailoring national sea-level projections for their eventual use in adaptation planning. VLM also has important implications for how sea level information is communicated to decision makers and stakeholders.

How to cite: Simpson, M. J. R., Bonaduce, A., Borck, H. S., Breili, K., Breivik, Ø., Ravndal, O. R., and Richter, K.: Sea-Level Rise and Extremes in Norway: Observations and Projections Based on IPCC AR6, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5229, https://doi.org/10.5194/egusphere-egu26-5229, 2026.

The Glacial Isostatic Adjustment (GIA) is the deformation of the Earth in response to changes in the cryosphere. It can produce significant uplift rates up to 1.5 cm/yr in North America. Therefore, it is crucial to remove these signals from space-based gravimetry and altimetry missions to improve our understanding of sea-level changes or to better assess other geophysical processes like ice-mass loss in Antarctica. Specifically, GIA in Antarctica remains poorly constrained due to the lack of in situ observations and the absence of paleo-shorelines dating. To compensate this observational gap, combinations of geodetic and gravimetry observations have been proposed. Wahr et al. (1995, doi:10.1029/94GL02840) introduced the ratio between rates of surface gravity changes and vertical displacements with a value of –0.15 microGal/mm and Sato et al. (2012, doi:10.1029/2011JB008485) theoretically showed that this ratio varies spatially and temporally. In this study, we investigate this ratio more thoroughly. We use the Love number formalism to compute gravity rates and vertical velocities induced by several ice-loading histories for a radially layered spherical Earth using the ALMA and TABOO software packages. We specifically assess the effect of different viscosity profiles and rheological laws such as Maxwell, Andrade, and Burger as a function of spatial wavelength and timing of the glacial history.

How to cite: Cambours, C., Mémin, A., and Tregoning, P.:  About gravity rates to vertical velocities ratio induced by ice-sheet changes in Antarctica , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5471, https://doi.org/10.5194/egusphere-egu26-5471, 2026.

Stress changes , such as those imposed by to earthquakes or ice mass loss, lead to viscous relaxation in the Earth’s interior. Stress relaxation is often modelled using steady-state rheological behaviours, based on linear diffusion creep or power-law stress dependence creep. However, rock mechanical experiments and microphysical models show that steady-state flow is always preceded by a transient phase, during which resistance to shear stress can be orders of magnitude lower than at eventual steady state, which leads to higher strain rates than predicted by steady-state flow laws.

We are interested in the effects of transient upper-mantle deformation on surface deformation of the Earth. Deformation at the grain scale can be accommodated by different types of defects in the crystal lattice. We focus on the role of dislocations and their elastic interactions in olivine grains. We use a flow law for dislocation creep that includes the effect of dislocation interactions on strain rates and evolution of dislocation density with strain and time. This flow law is based on new experimental and theoretical work on olivine. It has two main elements: 1) dislocation interactions reduce the amount of available stress driving motion of dislocations and thus of the rate of dislocation creep; 2) evolution of dislocation density is affected by viscous creep. This model leads to transient high strain rates in environments where stress is changing and steady-state (approximately power-law) behaviour sufficiently long after a stress change.

We use the finite element platform (GTECTON) to model the viscoelastic response to surface loads, such as hydrological loading or the loads of melting glaciers. The transient deformation involved may result in fast and slow deformation at different time scales, so numerical stability can become an issue. The sharp non-linearity of the flow laws plays an important role in this instability. The size of time steps in the models is a crucial factor in stability, and leads to a trade-off between accuracy and efficiency. In this study we explore implicit  time marching strategies to improve the numerical stability and accuracy of the solutions. This allows us to run efficient models of solid earth deformation for problems in which loads are rapidly changing, where we aim at building a better understanding of the time dependent strength of the upper mantle.

How to cite: Broerse, T., Van Calcar, C., Breithaupt, T., Govers, R., Ioannidi, I., Wallis, D., and Riva, R.: Fast viscous flow in the upper mantle: numerical stability in finite element models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5629, https://doi.org/10.5194/egusphere-egu26-5629, 2026.

Tidal forcing induces significant deformation of the Earth, investigated as early as the 19th century by Kelvin and later formalized by Love through the Love number formalism. The viscoelastic response of Earth’s mantle is traditionally modelled using the Maxwell rheology, and more rarely using the Burgers rheology. This work presents a comparative analysis of four viscoelastic rheological models: the Maxwell, Burgers, Andrade, and Sundberg–Cooper models. Although rarely used for the Earth, the Andrade and Sundberg–Cooper models have proven to be relevant for other planetary bodies. Theoretical responses have been developed for these models over a broad frequency range, from the seismic band to very long periods. Model predictions are compared with observations from the IGETS (International Geodynamics and Earth Tide Service) worldwide network of superconducting gravimeters, low-degree time-varying space gravity measurements, and length-of-day variations to better constrain Earth’s mantle rheology and viscosity.

How to cite: Saad, T., Boy, J.-P., and Rosat, S.: Constraining Mantle Rheology with Long-Period Tides:Modeling Earth Tidal Response with Maxwell, Burgers, Andrade, and Sundberg-Cooper models and comparison with superconducting gravimeters, low-degree time-variable gravity & length-of-day observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7241, https://doi.org/10.5194/egusphere-egu26-7241, 2026.

The future stability of the Antarctic Ice Sheet is determined by the marine ice sheet instability (MISI), an amplifying feedback, leading to potentially irreversible retreat. Glacial isostatic adjustment (GIA) potentially provides a stabilizing feedback, yet its influence on the timing and nature of ice-sheet tipping dynamics remains poorly constrained. Using an ensemble of idealized simulations in a synthetic Antarctic-type ice-sheet–shelf system, we systematically investigate how interactions between ice dynamics and the visco-elastic solid Earth affect MISI tipping dynamics under increasing basal ice-shelf melt. We find that the critical thresholds for bifurcation tipping strongly depend on the timescale and spatial extent of Earth deformation, increasing substantially (order of magnitude) relative to a fixed-bed (rigid) case.

For half of the ensemble members, rate-induced tipping occurs when melt rates increase sufficiently rapidly, triggering MISI before the threshold for bifurcation tipping is reached and reducing the effective tipping threshold by up to 80%. Bed uplift cannot halt MISI once initiated, due to rapid grounding-line retreat. We further identify grounding-line overshoots and self-sustained oscillations driven solely by internal ice - Earth interactions.

We find similar dynamics in more realistic simulations of the Antarctic Ice Sheet with a coupled ice sheet - solid Earth and sea-level model considering a three-dimensional Earth structure. Our results highlight that both the magnitude and rate of future climate forcing critically influence Antarctic ice-sheet stability.

How to cite: Albrecht, T., Feldmann, J., Klose, A. K., Wullenweber, N. K., Mojtabavi, S., Klemann, V., and Winkelmann, R.: Rate-induced tipping of ice sheets interacting with the visco-elastic solid Earth, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9816, https://doi.org/10.5194/egusphere-egu26-9816, 2026.

How to cite: Schachtschneider, R., Klemann, V., Steinberger, B., and Thomas, M.: Effects of uncertainty in mantle viscosity structure inferred from seismic tomography on glacial isostatic adjustment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9831, https://doi.org/10.5194/egusphere-egu26-9831, 2026.

Glacial isostatic adjustment (GIA) is identified as a crucial feedback mechanism between ice-sheet dynamics and viscoelastic deformation of the solid Earth. In addition, the interpretation of geodetically inferred ice-mass change requires the consideration of a realistic GIA correction. Specifically in Antarctica, regions of low mantle viscosity can significantly impact ice sheet dynamics due to different feedback strengths.

In this study we discuss the effect of lateral viscosity contrasts on the response of the solid Earth to ice-mass changes in view of bedrock displacement and geoid change. Considering different geometries of low-viscosity bodies, we infer their impact on geodetic observables. As the main question we will investigate to which extent geodetically inferred viscosity values are biased due to the fact that, in general, they are based on assuming a  viscosity structure that only varies with depth. Furthermore, such structural features might also impact the interaction between the solid-Earth and the Antarctic ice-sheet dynamics.

This work contributes to the German Climate Modeling Initiative PALMOD.

How to cite: Klemann, V., Schachtschneider, R., Wullenweber, N., Albrecht, T., and Scheinert, M.: Impact of lateral and radial viscosity variations on vertical land motion in view of Antarctic GIA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9924, https://doi.org/10.5194/egusphere-egu26-9924, 2026.

Glacial isostatic adjustment (GIA) induces lithospheric bending that can strongly influence depositional systems located within ice-sheet forebulges. While previous studies have documented the role of GIA in river-network reorganization during the last glacial cycle, its impact on sedimentary systems earlier in the Quaternary remains poorly constrained.

Here, we investigate the pre-glacial Daumantai Formation, exposed in several outcrops beneath the oldest tills in the Baltija Highlands of eastern Lithuania. This fluvial succession was dated using combined ¹⁰Be–²⁶Al exposure–burial dating to ~0.95 ± 0.1 Ma, while the same approach indicates that the overlying tills were deposited only ~30–50 kyr later. Importantly, the succession records a distinct change in palaeocurrent directions, initially toward the southeast and subsequently toward the northwest, occurring prior to the first documented advance of the Fennoscandian Ice Sheet (FIS) into the region. This shift is interpreted as a reorganization of the river network rather than merely a modification of river planform geometry, as the palaeocurrent reorientation is consistently documented at several sites across distances exceeding 10 km.

GIA was simulated using the ICEAGE normal-mode modelling framework to assess the potential role of lithospheric bending and associated slope changes in river-network reorganization. Four ice-sheet configurations were tested: (1) a late Gauss and (2) an early Matuyama extent after Batchelor et al. (2019, https://doi.org/10.1038/s41467-019-11601-2), (3) an additional, larger ice sheet extending ~150 km northwest of the study area, and (4) a MIS 20–24 ice-sheet extent from Batchelor et al., which directly overlies the analysed succession. A 380 kyr modelling scenario included five glacial cycles comprising ice growth, deglaciation, and ice-free periods, with 40 kyr and 100 kyr periodicities and increasing amplitudes. The modelling results indicate that the study area was affected by forebulge development associated with all tested ice-sheet extents. The two smaller ice sheets induced southeastward surface tilting, whereas the larger configuration produced northwestward tilting, with maximum slope changes reaching ~0.002°.

The resulting time-dependent uplift and subsidence fields were subsequently used as inputs for landscape evolution modelling to investigate the impact of episodic glacial loading and unloading on surface processes. Erosion and sedimentation were simulated using a stream-power–law, finite-difference approach under imposed time-varying three-dimensional deformation. Preliminary results suggest that repeated north–south tilting associated with glacial cycles exerts a strong control on fluvial dynamics and can locally lead to drainage reversals.

The postdoctoral project CosmoLith was caried out under the “New Generation Lithuania” plan (Nr. 10-036-T-0008) financed under the European Union economic recovery and resilience facility instrument NextGenerationEU. The research was supported by the Slovak Research and Development Agency under the contract No. APVV-21-0281.

How to cite: Šujan, M., Bitinas, A., Steffen, H., Balázs, A., Gedminienė, L., Kováčová, M., Chyba, A., Damušytė, A., Pan, R., Aherwar, K., and Rózsová, B.: Testing glacial isostatic adjustment as a cause of Early Pleistocene river network reorganization in the area of Lithuania (NE Europe), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10025, https://doi.org/10.5194/egusphere-egu26-10025, 2026.

Reducing uncertainties in the projections of the future contribution of the Antarctic Ice Sheet (AIS) to global sea-level rise is crucial for coastal communities and policymakers worldwide. Self-amplifying feedback mechanisms can lead to accelerated and irreversible ice loss once certain temperature regimes are crossed. Such tipping behaviour will ultimately lead to a new equilibrium state, even if boundary conditions remain constant. In contrast, negative feedback loops, such as the sea-level feedback due to glacial isostatic adjustment (GIA), potentially slow down the rate of ice loss by reducing the local water depth at the grounding line. The rebound rate of the bedrock following a reduction in ice mass depends heavily on the Earth structure beneath Antarctica, with mantle viscosities and corresponding response timescales that can vary laterally by two to three orders of magnitude. Yet, it is unclear whether GIA feedbacks can shift ice sheet tipping points or even prevent tipping as a result of path dependency, as bifurcation-tipping theory considers stationary states only, where the ice sheet load and solid Earth deformation are in isostatic equilibrium.

By employing different Earth structures in (quasi-)equilibrium simulations and varying temperature forcing rates, using a 3D coupled ice sheet–GIA model (PISM-VILMA), we explore their influence on the AIS's stability and tipping thresholds, focusing on the West Antarctic Ice Sheet and the Wilkes Subglacial Basin. Our simulations demonstrate that the Earth structure significantly affects both the temperature threshold at which self-sustained retreat of the AIS is initiated and the long-term committed contribution to global sea-level rise; this as a result of path dependency.
Moreover, our results highlight the competing timescales of ice sheet and solid Earth dynamics. We find that the rate of temperature increase represents a crucial parameter. Rate-induced tipping can lead to abrupt changes at lower thresholds than in the quasi-equilibrium case, in particular for stronger Earth structures, leading to higher sea-level contribution for the same warming levels.

How to cite: Wullenweber, N., Albrecht, T., Mojtabavi, S., Klemann, V., and Winkelmann, R.: The impact of Earth structure on Antarctic ice sheet tipping thresholds, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10748, https://doi.org/10.5194/egusphere-egu26-10748, 2026.

The Greenland Ice Sheet (GrIS) is currently undergoing substantial mass loss, with major consequences for both the Earth system and human societies, including a significant contribution to the ongoing acceleration of global mean sea level rise. Accurately estimating the GrIS mass balance therefore represents a major focus of current research. However, it remains challenging and, to date, still imprecise.

One of the main reasons is Glacial Isostatic Adjustment (GIA) - the viscoelastic response of the solid Earth to the growth and decay of ice sheets at its surface. Because geodetic observations are among the most used tools to quantify ice mass changes, robust estimates of GIA corrections are essential for the accurate interpretation of these measurements.

This study focuses on deformations induced by ice mass loss since the Little Ice Age (LIA) and their impact on present-day vertical land motion inferred from GNSS observations. Using a reconstructed history of the GrIS and its peripheral glaciers, we model LIA-driven viscoelastic deformations assuming different Earth models, exploring a range of values for two rheological parameters: the lithosphere thickness and the upper mantle viscosity. These simulations, combined with corrections for GIA associated with the last glacial maximum and the elastic response to contemporary ice melting, are compared against GNSS observations. Our results explain the uplift rates at most of the GNSS stations and are consistent with existing literature, with LIA-induced vertical land motion best accounted for by a 160 km thick lithosphere and an upper mantle viscosity of 2.73 × 10¹⁹ Pa·s.

As we explore the rheological structure beneath Greenland, we pay particular attention to the southeastern region, where uplift rates are unusually high. Southeastern Greenland exhibits significant lateral variations in mantle viscosity and lithospheric thickness, likely related to the track of soft material left by the Iceland hotspot. Our simulations support the presence of a low viscosity/thin lithosphere zone in this region, and we further investigate its effects by adding to our modeling an asthenospheric layer within the upper mantle.

Overall, this study demonstrates that deformations induced by the LIA constitute a non-negligible contribution to present-day geodetic signals. Accounting for this component is therefore essential to reduce uncertainties in ice mass balance estimates and to better understand Greenland’s contribution to global sea level rise.

How to cite: Gourrion, E., Métivier, L., and Greff-Lefftz, M.: The influence of LIA-induced viscoelastic deformations on geodetic observations in Greenland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12406, https://doi.org/10.5194/egusphere-egu26-12406, 2026.

Systematic subsidence of ~1 mm/yr is observed across the Pacific at GNSS sites on islands that lack significant local tectonic and volcanic processes (Altamimi et al., 2023; Ballu et al., 2019; Hammond et al., 2021).  However, the horizontal motion of these sites is well described by Pacific plate motion.  This suggests that the observed subsidence represents a deeply rooted geophysical signal, rather than just localized deformation. 

Both ongoing and past ice mass redistribution are known to produce global deformation. Previous models of recent global ice mass redistribution (Coulson et al., 2021; Riva et al., 2017) predict tenths of a mm/yr of subsidence in far field locations such as the Pacific.  In addition, post-LGM GIA models like ICE-6G also predict subsidence in the Pacific on the order of tenths of a mm/yr.

Here we evaluate three new models of the global deformation associated with present day ice mass redistribution. These models use the methods of the elastic loading model originally published by Coulson et al. (2021), utilizing new mass change estimates with increased spatial and temporal coverage as input. The three updated models all use Velicogna et al.’s (2020) mass change estimates for the Antarctic and Greenland ice sheets, paired with global glacier mass change estimates from either Ciraci et al. (2020), the Copernicus group (Dussaillant et al., 2024), or Hugonnet et al. (2021). These models are evaluated at selected GPS sites near field to glaciers in regions such as SE Alaska, Greenland, etc., as well as 27 Pacific GPS sites located far field from ice mass change. We also use these far field sites to evaluate 39 different long-term GIA models that predict the present-day viscoelastic response of the earth to past loading. 

We find that all three models of elastic deformation due to recent global ice mass change produce very similar results in the far field. The most significant differences in the models are seen in the near field in SE Alaska and Svalbard. Additionally, there is a set of 15 long-term GIA models that improve the fit of both the horizontal and vertical observations in the Pacific when used in combination with an ongoing cryospheric loading model to correct the GPS data. Overall, we find that the sum of the deformation due to ongoing ice mass changes and long-term GIA explains about half of the subsidence signal that we observe in the far field. 

Studies of the contribution of different components of barystatic sea level (BSL) suggest that though cryospheric melting is the largest contributor, non-cryospheric terrestrial water storage (TWS) could be responsible for ~17 – 25% of BSL over the past couple of decades (Nie et al., 2025; McGirr et al., 2024).  Since changes in TWS may represent a non-trivial global loading signal, we choose to also consider if deformation associated with TWS may explain part of the residual ~0.5 mm/yr subsidence signal that we see in the far field after our cryospheric loading corrections.

How to cite: Vance, K., Freymueller, J., and Coulson, S.: Evaluating global models of deformation from ongoing ice mass changes and long-term GIA, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13801, https://doi.org/10.5194/egusphere-egu26-13801, 2026.

During the last deglaciation, the retreating Laurentide Ice Sheet made way for massive proglacial lakes to form and then drain. In a similar fashion, dramatic changes in climate over the deglaciation were reflected in changing groundwater storage through time. We evaluate the impacts of these long-term changes in water storage on Glacial Isostatic Adjustment (GIA) in North America. To do so, we couple the Water Table Model (WTM) – which simulates depth to water table – with a gravitationally self-consistent GIA model to find both changing lake and groundwater storage volumes, and the impacts that these have on changing GIA. 

Our WTM results show an evolving water table that includes proglacial and pluvial lakes consistent with the geological record. Lake and groundwater loading deflect topography by tens of metres at some locations. Because depth to water table is topography-dependent, we repeat our WTM simulation using updated topographic inputs and find that water table depth is modified by several metres at some locations. The results are highly heterogeneous, reflecting that GIA and hydroclimate together drive long-term water-table change. 

How to cite: Callaghan, K. L., Wickert, A. D., and Austermann, J.: Glacial isostatic adjustment under a changing groundwater load since the Last Glacial Maximum, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15241, https://doi.org/10.5194/egusphere-egu26-15241, 2026.

The deglacial forebulge along the Atlantic coasts of North America and Europe has been a key area for glacial isostatic adjustment (GIA) studies. Relative sea level (RSL) changes in this region are highly sensitive to the 3D Earth structure, and the area hosts abundant RSL data that can help constrain the 3D Earth structure. However, many previous studies either relied primarily on 1D Earth models or adopted 3D structures without systematically exploring the magnitude of lateral heterogeneity or the uncertainty associated with deglacial ice histories.

Here, we use the latest standardized deglacial RSL databases from the Atlantic coasts of North America and Europe for comparison with 3D GIA models coupled with two widely used ice models, ICE-6G_C and ANU-ICE. Our 3D Earth model consists of a 1D background viscosity model (η_o) and lateral viscosity variations; the latter are derived from shear velocity anomalies in a seismic tomography model and scaled by a factor (β) denoting the magnitude of lateral heterogeneity. We explore a range of η_o and β to assess the sensitivity of RSL predictions to both the background viscosity and the magnitude of lateral heterogeneity. The RSL databases include sea-level index points and limiting data, which we further classify by depositional setting (base of basal, basal, intercalated). We compare the RSL data to the GIA model predictions using a weighted misfit approach that reflects data type and interpretive uncertainty.

We find that 3D Earth structure has significant influence on RSL predictions, and the optimal 3D models substantially improve the fit to RSL data compared with 1D GIA models (e.g., ICE-6G_C VM5a). The Atlantic coast RSL datasets from North America and Europe favor different combinations of η_o and β, although the former provides stronger constraints owing to its higher spatial coverage and lower data uncertainty. Notably, despite differences in ice history, ICE-6G_C and ANU-ICE prefer similar 3D Earth structures. Ongoing work will quantify the uncertainty of the 3D model resolved by the available RSL data.

How to cite: Li, T. and Walker, J.: 3D Glacial Isostatic Adjustment along the deglacial forebulge of the Atlantic coasts of North America and Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15680, https://doi.org/10.5194/egusphere-egu26-15680, 2026.

The glacial isostatic adjustment (GIA) and sea level modeling communities have historically lagged other fields in adhering to the FAIR principles of making model outputs findable, accessible, interoperable, and reusable – a delay that has slowed scientific discovery. While sharing model outputs has improved recently, usability of available outputs continues to be hindered by lack of standardization. Meanwhile, legacy model outputs can be lost as the technology storing them grows obsolete and their creators retire or leave academia.

The GIAmachine initiative addresses this problem. GIAmachine aims to make accessible as many published GIA and sea level model outputs as are retrievable by

• cataloguing and standardizing published GIA and sea level model outputs; 
• contacting authors of published-but-inaccessible models to encourage them to upload their outputs to DOI-minting repositories;
• partnering with the GHub science gateway to make a long-term home for these newly available outputs;
• building Jupyter notebooks on GHub that make these models interoperable and easy to use; and 
• encouraging the GIA and sea level modeling communities to follow the FAIR principles. 

Our poster will introduce the GIAmachine online portal and outline outstanding challenges. We appreciate community input for designing a living resource that meets the specific needs of current and future scientists.

How to cite: Steffen, H., Creel, R. C., Kodama, S. T., Tulenko, J. P., Steffen, R., Riva, R. E. M., Quinn, J., and Briner, J. P.: GIAmachine: a community-driven rescue and recovery initiative for legacy sea level and glacial isostatic adjustment modeling data, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16724, https://doi.org/10.5194/egusphere-egu26-16724, 2026.

We present a new relative sea level (RSL) database for Norway and for modelling studies. The total database contains 1011 data points, of which 558 (55%) are index points and 453 (45%) limiting dates. The new RSL database differs from earlier efforts in two key ways. Firstly by having fewer limiting dates as we have removed redundant data. Secondly, it contains new RSL data collected over 2018-2024 which are largely index point data.

The new RSL database is compared to 9,900 ice-Earth combinations from a 1-D glacial isostatic adjustment (GIA) model. From these combinations, the ice models tested come from a high-variance subset of 10 Eurasian Ice Sheet chronologies. These (GLAC3) chronologies are from a last glacial cycle history matching of the physics-based Glacial Systems Model against a diverse set of constraints. The 10 Eurasian ice chronologies are combined with 3 different reconstructions of global ice changes (i.e., a total of 30 ice models). 

We show how data-model fits vary for the ice chronologies and Earth model parameters explored. Results indicate relatively weak upper mantle viscosities for Norway. While some ice-Earth model combinations can reproduce the general RSL trends and show features of the Younger Dryas and Tapes transgressions, no model parameter sets provide quality fits to all the data or can follow all the observed RSL fluctuations. This suggests inaccuracies in the model and/or the need to explore a larger parameter space.

RSL uncertainties are calculated using a nominal Bayesian approach and capture ~80% of the Norwegian RSL data. By splitting the data into 3 subregions, we show how data-model fits vary geographically and which ice-Earth model combinations are preferred where. This reveals that data-model fits are poorest in South Norway, where only 40% of the RSL are captured (and only 22% of the index point data). We hypothesise that the poor fits in this region are due to inaccuracy in the regional and/or background (global) ice models considered.

How to cite: Simpson, M. J. R., Parang, S., Lakeman, T., Milne, G. A., Love, R., and Tarasov, L.: A new relative sea level database for Norway tested against glacial isostatic adjustment models with an ensemble of physics-based history-matched Eurasian Ice Sheet chronologies. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19132, https://doi.org/10.5194/egusphere-egu26-19132, 2026.

Horizontal deformation data are not commonly used as constraints in Glacial Isostatic Adjustment
(GIA) studies. In GIA modelling, horizontal displacements are more sensitive to the elastic structure
of the Earth than vertical displacements. Reliable modeling of horizontal motion can therefore help
constrain further lithospheric elastic properties and allow for more realistic stress calculations, which
can be used in studies of e.g. fault stability and magma migration modulated by GIA induced stresses.
Previous GIA benchmarking studies have shown that, for incompressible models, vertical displace-
ments produced by flat-Earth Finite Element (FE) models compare well with solutions obtained using
the spherical harmonic method, whereas horizontal displacements may be significantly biased. The
more recent study by Reusen et al. (2023), focusing on compressible flat-Earth FE models, showed
good agreement in horizontal displacements between FE model with elastic foundations at each density
contrast and spherical harmonic solutions, with progressively improved agreement for decreasing load
radius. However, vertical displacements for the compressible case were not examined. In this specific
case, compressibility is implemented only partially through the so-called material compressibility, which
accounts for volume changes but neglects density variations.
Modelling present-day GIA in Iceland requires small load radii, low mantle viscosities, and thin
elastic lithospheres—parameter ranges that have not yet been fully benchmarked. Here, we extend the
study of Reusen et al. (2023) by considering glacier loads and Earth structures closer to those of Iceland
at the present day glacial retreat. In addition, we also benchmark the vertical displacement. We use a
flat-Earth, material compressible model with an elastic layer overlying a Maxwellian viscoelastic mantle,
applying spring foundations to every density contrast. Our goal is to identify strategies to obtain reliable
displacement and stress outputs from Icelandic GIA models, while quantifying uncertainties in mantle
viscosity and elastic thickness. Our study highlights the importance of benchmarking small icecaps and
thin lithospheres to be used in studies of small glaciated regions.

References
Reusen et al. (2023). “Simulating horizontal crustal motions of glacial isostatic adjustment using
compressible cartesian models”. In: Geophysical Journal International 235(1), pp. 542–553.

How to cite: Bellagamba, G., Schmidt, P., Geirsson, H., Givens, T., and Steffen, H.: Benchmarking Horizontal and Vertical Deformation in Material Compressible Finite Element Models of Glacial Isostatic Adjustment of Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21552, https://doi.org/10.5194/egusphere-egu26-21552, 2026.

Global Navigation Satellite System (GNSS) data provide critical insights into solid Earth deformation. GNSS observations at bedrock in glaciated areas like Antarctica serve as essential constraints to model the glacial isostatic adjustment (GIA). Likewise, they may serve to aid the empirical estimation of GIA and of ice-mass balance. Since the last International Polar Year 2007/08, GNSS coverage has significantly been expanded in West Antarctica, the Antarctic Peninsula, and parts of Victoria Land. In East Antarctica, however, logistical challenges and sparse bedrock outcrops have limited the establishment and (re-)observation of new GNSS stations.

In order to address this gap, a GNSS network of mostly episodic site was deployed across western and central Dronning Maud Land, East Antarctica. Measurements were initiated in the mid-1990s while the most recent observation campaign was conducted during the 2022/2023 Antarctic season. Additionally, two new permanent GNSS sites were installed in western Dronning Maud Land in the beginning of 2020.

This study presents results from a consistent analysis of both episodic and continuous GNSS datasets over a time span of more than 20 years. We demonstrate how this extended temporal coverage enhances the accuracy of secular trends derived from GNSS time series. To isolate the GIA displacement signal, we account for elastic displacement caused by present-day ice mass changes using satellite altimetry and surface mass balance models. The resulting trends are compared to GIA estimates inferred from a number of models. Thus, we come up with new insights into the deformation pattern in a region that lack respective information so far. Our findings emphasize the importance of long-term GNSS measurements in refining GIA models for East Antarctica.

How to cite: Scheinert, M., Buchta, E., Kappelsberger, M., Eberlein, L., and Willen, M.: Investigation of glacial isostatic adjustment in Dronning Maud Land, East Antarctica, using long-term GNSS observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22615, https://doi.org/10.5194/egusphere-egu26-22615, 2026.

Precise seafloor geodetic measurements are essential for understanding plate tectonics, earthquake cycles, and volcanic activity. Seafloor pressure gauges provide a key tool for monitoring vertical changes in the seafloor elevation. However, distinguishing millimeter-scale tectonic signals from instrumental drift and environmental noise remains a fundamental challenge in deep-ocean observing.

This presentation evaluates the performance and data integrity of self calibrating bottom pressure recorders (BPR) deployed by Ocean Networks Canada (ONC) offshore Vancouver Island. Instruments like the RBR BPRZero and the Sonardyne FETCH AZA utilize Ambient-Zero-Ambient (AZA) in-situ calibration mechanisms to quantify sensor drift. The AZA method involves switching a pressure gauge from ambient (seafloor) pressure to atmospheric pressure within the instrument's housing. By comparing this internal pressure reading to an accurate barometer also measuring internal pressure, the drift can be precisely determined and a calibration function applied.

A forensic analysis of the dataset reveals that, while the high-resolution pressure measurements capture true genuine environmental signals, they are also significantly contaminated by instrumental artifacts that are partially related to the measurement approach itself. In this study we report findings from preliminary deployments and discuss the methodological challenges encountered, proposing mitigation strategies for future applications.

How to cite: Schlesinger, A., Heesemann, M., Dexter, J., Leconte, J.-M., Davis, E., Sun, T., Kreimer, N., and Aghaei, O.: Assessing Data Integrity in Seafloor Geodesy: An Analysis of Self-Calibrating Pressure Data Collected by Ocean Networks Canada, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1585, https://doi.org/10.5194/egusphere-egu26-1585, 2026.

Ocean Bottom Pressure gauges (OBPs) are devices installed on the seafloor to continuously measure ocean bottom pressure. They are expected to detect vertical seafloor crustal deformation caused by transient tectonic events. However, OBP data contain pressure changes originating from various sources other than tectonic events, such as ocean tides, non-tidal fluctuations due to meteorological and oceanic variations, and instrumental drift. We need to remove these non-tectonic components to identify the pressure changes related to vertical crustal deformation. However, the timescale of non-tidal fluctuations (ocean noise) is similar to that of transient tectonic signals, such as slow slip events (SSEs), which makes it difficult to separate these components.

Otsuka et al. (2023) applied principal component analysis (PCA) to seafloor pressure data obtained by an OBP array to detect transient events, assuming that pressure changes due to transient events cause temporal fluctuations in the PCA results. To verify the performance of this method, they applied PCA to synthetic data and confirmed that the method can detect temporal changes in the composition of principal components (PCs). In the present study, we apply this method to OBP data obtained before the 2011 Tohoku earthquake, which includes transient events resulting from aseismic slip, as reported by Ito et al. (2013), to verify whether we can identify the event through temporal changes in the PCs decomposed from the OBP data. We performed PCA on de-tided OBP data covering about four months before the Tohoku earthquake using a short sliding time window, to examine temporal variations in the PCs.

Changes in the PCs were evaluated using the normalized inner product (NIP) of the eigenvector of each PC (Otsuka et al., 2023), which measures the difference in the direction of the vector. We expect the NIPs to be stable if the OBP data do not contain any transient events, whereas evident changes in the NIPs of more than one PC would occur when transient pressure variations are included in the data. In the present study, the NIPs of PC1 (the most significant component) and PC2 (the second most significant component) remained stable over time, whereas the NIPs of PC3 and PC4 began to decrease as the moving window (60-day length) approached late January 2011 and remained low for about 40 days. Based on a comprehensive analysis of seismic and geodetic data, including the same OBP data, Ito et al. (2013) reported that an SSE lasted for about 40 days from late January 2011. The NIP changes detected in the present study may correspond to pressure changes due to this transient event.

How to cite: Yamada, T., Hino, R., Kubota, T., Otsuka, H., and Ohta, Y.: An Attempt to Detect Transient Crustal Deformation from Ocean Bottom Pressure Gauge Data Using Principal Component Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3717, https://doi.org/10.5194/egusphere-egu26-3717, 2026.

High-precision seafloor geodesy such as GNSS-A positioning or seabed transponder networks is critically dependent on acoustic travel time measurements to recover seafloor benchmarks; however, in stratified ocean acoustic ranging, sound-speed-profile variations invalidate the approximately linear travel-time-to-range mapping that commonly holds for the terrestrial case. Simplified sound-speed models therefore yield biases that could be aliased into deformation time series, leading to errors in inference of plate motions and lithospheric deformation. Furthermore, underwater transponders deployed within the geodetic network are unable to maintain strict time synchronization in cold, high-pressure deep-ocean environments, imposing an added challenge on the usage of travel-time ranging.

To overcome these limitations, we develop an equivalent-gradient framework with a closed-form delay–range relationship and represent synchronization imperfections by a lumped time-bias term, enabling joint recovery of seafloor transponder position(s) and the bias. Specifically, let k = 1,...,K index the reception epochs along a moving surface vessel trajectory; s_k denotes the GNSS-referenced vessel position and t_k the recorded one-way arrival timestamp from a fixed seafloor transponder. We then form inter-epoch TDOA measurements that eliminate the unknown transmit epoch and reduce the problem to estimating a reference one-way delay τ₀ together with the transponder location u. Under the equivalent-gradient framework, travel time is efficiently mapped to an slant range dk = Req (τ; ξ_k),  , where ξ_k collects the equivalent-gradient parameters derived from the layered SSP, yielding the range–geometry constraints dk^2 = u − s^2. A squared-difference with respect to a reference epoch leads to a stable pseudo-linear regression:

This yields a WLS closed-form initializer followed by weighted Gauss–Newton refinement. An SDR-based global initializer is also developed, offering complementary insight into the problem’s geometry. The approach accommodates different acoustic link geometries (e.g., ship-to-seafloor and AUV-to-seafloor) and can exploit identifiable multipath (e.g., surface-reflected arrivals) for additional constraints. Monte-Carlo simulations under realistic stratified SSPs provide a controlled assessment of performance and robustness, showing that the proposed method substantially reduces range bias and improves seafloor position recovery relative to constant-sound-speed and single-gradient baselines, while remaining stable under SSP mismatch.

We further present an underwater acoustic transponder prototype integrating a chip-scale atomic clock (CSAC) and an FPGA-based multi-channel parallel clock disciplining subsystem.Sea trials in the South China Sea validate the end-to-end design and demonstrate representative ranging results, confirming kilometer-scale capability and stable real-time performance under in situ conditions. Overall, the proposed approach improves the fidelity of seafloor positioning time series and strengthens geodetic constraints on ilithospheric deformation and related earthquake hazard assessment.

How to cite: Liu, Z., Zhou, F., Zhao, J., Ji, X., and Cao, C.: Equivalent-Gradient Sound-Speed Correction and Joint Time-Bias Estimation for Stratified-Ocean Acoustic Ranging in Seafloor Geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3939, https://doi.org/10.5194/egusphere-egu26-3939, 2026.

Continuous observations of seafloor water pressure, which enable detection of vertical seafloor motion, are an essential technique in seafloor geodetic observations. For such geodetic applications, observation instruments equipped with Digiquartz sensors manufactured by Paroscientific Ltd. are commonly used because of their extremely high accuracy, resolution, and stability. Downsizing of observation instruments are important for making dense network allowing detection of subtle crustal deformation; however, the relatively high power consumption of Digiquartz makes it difficult to downsize self-pop-up mobile observation systems.

Our group has used RBRduo3, temperature–pressure loggers as auxiliary instruments to monitor environmental conditions in other seafloor observations, such as seafloor acoustic ranging. Given that these products are compact, lightweight, and capable of easily acquiring continuous records over periods exceeding one year, we investigated their potential applicability to seafloor geodetic observations. To this end, we conducted parallel observations with ocean-bottom pressure recorders (OBPRs) equipped with high-precision Digiquartz sensors and RBR loggers.

Pressure records from RBR loggers exhibit large transient variations immediately after deployment on the seafloor, with amplitudes up to about an order of magnitude larger than the typical transients observed in Digiquartz sensors. However, except for approximately the first three days after installation, this behavior can be well approximated by a time-dependent function combining an exponential term and a linear term, and no other irregular fluctuations are observed.

Results from parallel observations at sites with water depths exceeding 5,000 m show that, aside from the initial post-deployment transients, pressure time series obtained by RBR loggers agree well with those from Digiquartz sensors. In contrast, at shallower sites with water depths less than about 2,000 m, the pressure time series from the two instruments differ substantially. The time series of the pressure differences closely resembles the temperature time series, suggesting that these discrepancies arise from insufficient temperature correction of the RBR pressure data.

Assuming that apparent pressure variations caused by temperature changes dominate the short-period components of the pressure fluctuations recorded by the RBR logger, we estimated a coefficient for temperature correction by minimizing the power of the fluctuations. Using this coefficient, we removed the temperature-correlated component over the entire frequency band. As a result, we obtained pressure time series that agree with those from the Digiquartz sensors within approximately 0.2 hPa in the parallel observations. This demonstrates that, with appropriate temperature correction, it is possible to obtain pressure variation data from RBR loggers that are comparable in quality to those from Digiquartz sensors.

By taking advantage of their compact size and low power consumption, RBR loggers could be applied as add-on instruments to ocean bottom seismometers and similar seafloor observation instruments, and are expected to contribute to an increased number of observation points in mobile seafloor observation networks.

How to cite: Hino, R., Suzuki, S., Sato, M., Yamada, T., and Ohta, Y.:  Quality assessment of seafloor pressure data from RBR loggers for applications to seafloor geodesy, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6150, https://doi.org/10.5194/egusphere-egu26-6150, 2026.

The Quaternary Olkaria volcanic complex is a high-temperature geothermal system in the Central Kenya Rift located in a structural transition zone between the Mt. Longonot and Mt. Eburru eruptive centers. This region is subject to protracted crustal deformation and ground subsidence. Vertical ground motion is associated with crustal-scale processes, including magmatic intrusion and eruption, as well as normal and transfer faulting. In addition, the region has been the subject of fluid extraction associated with geothermal energy production. In the past 20 years, increased re-injection strategies were implemented in order to slow down drawdown and thereby mitigate against exponential ground subsidence. Although an extensive benchmark network for monitoring surface deformation was established in 1983, the lack of subsequent precise leveling surveys has necessitated the use of state-of-the-art geodetic techniques to quantify the magnitude and temporal evolution of ground deformation to better understand the roles of tectonic and anthropogenically induced land-surface changes.

Here we present new radar interferometry observations spanning the past decade, combining Sentinel-1 data (2016–2026) and TerraSAR-X data (2024–2026), to constrain vertical surface motion at high spatial and temporal resolution. These InSAR time series are complemented by measurements from a local GNSS network installed on and around the Olkaria dome. Our results show that rapid subsidence observed since 2016 slowed markedly around 2020 and has since largely stagnated. High-resolution X-band and persistent scatterer C-band data reveal that localized subsidence persists near fluid-extraction sites, whereas regional subsidence rates in the area of the volcanic complex have decreased by approximately an order of magnitude. Independent, statistically robust GNSS time-series analyses support these observations. We further assess different InSAR processing strategies and highlight the critical importance of rigorous atmospheric correction due to the influence of high seasonal moisture availability.

Overall, our analysis indicates that vertical land-surface deformation in the Olkaria region at annual timescales is primarily driven by deep-seated magmatic processes, while geothermal energy production has only contributed to localized subsidence through fluid extraction.

How to cite: Bookhagen, B., Kimata, J., Omenda, P., Saitet, D., and Strecker, M.: GNSS and InSAR observations at the Olkaria geothermal site in the central Kenya Rift System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8227, https://doi.org/10.5194/egusphere-egu26-8227, 2026.

 Ocean-bottom pressure (OBP) gauges are a key tool in seafloor geodesy, providing time-series observations of vertical seafloor motion by continuously recording pressure variations associated with changes in water depth. However, OBP time series contain multiple superimposed signals in addition to crustal deformation, including tides, instrumental drift, and non-tidal oceanic fluctuations driven by atmospheric and oceanic processes. In particular, non-tidal oceanographic fluctuations have time scales comparable to long-term crustal deformation, making it difficult to separate them and accurately estimate long-term seafloor deformation.

 Ocean-model-based corrections have been proposed to isolate and remove non-tidal oceanographic components, offering a physically based approach. However, model–observation mismatches can leave large residuals after correction, making it harder to identify deformation-related signals. As a fundamental step toward understanding these model–observation discrepancies, this study quantifies the physical processes controlling OBP variability using an ocean general circulation model named OFES2 (Sasaki et al., 2020), which does not assimilate oceanic observations.

 As a first step, we assess the extent to which OFES2 can account for the observed OBP variability by directly comparing modeled and observed time series. The modeled OBP is compared with observed OBP records from pressure gauges deployed off northeastern Japan. Our results show that OFES2 reproduces the seasonal cycle of the observed OBP time series to some extent, whereas agreement at periods of several days to about a month remains limited in both amplitude and phase.

 To investigate the physical processes controlling the modeled OBP variability, we decompose the modeled OBP into four components: atmospheric pressure loading, sea surface height variability, horizontal density advection, and vertical advection, and quantify the relative contribution of each component. The decomposition indicates that atmospheric pressure loading and sea surface height variability dominate the modeled OBP fluctuations, while horizontal density advection contributes to part of the seasonal variability. Moreover, correlation analyses using the time-derivative of the observed OBP and the decomposed pressure components reveal episodic enhancements in correlation with the horizontal density advection term, suggesting that its contribution can temporarily increase during specific periods.

 We will extend the analysis by comparing OFES2 with longer-term OBP observations and discussing in more detail the contributions of each component to seafloor pressure variability.

How to cite: Hagihara, T., Ohta, Y., Wang, S., Sasaki, Y., Hino, R., and Otsuka, H.: Process Decomposition of Ocean-Bottom Pressure Variability: What OFES2 Reproduces and Misses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8768, https://doi.org/10.5194/egusphere-egu26-8768, 2026.

Fault zones release tectonic strain through a combination of seismic and aseismic slip. Creeping fault segments may have typically less elastic strain energy accumulated available to rupture in an earthquake compared to largely locked sections. However, where creeping fault segments transition into locked ones, stress rates are the highest as the slip deficit and stored elastic strain show large spatial along-fault gradient.

The North Anatolian Fault Zone (NAFZ) in Türkiye hosts two prominent creeping segments: 1) the Ismetpasa segment on the central part of the NAFZ, which appears devoid of micro-seismicity down to magnitude M=1.8 in the regional catalogs, but hosted the nucleation of two M>7 earthquakes in 1943 and 1944; and 2) the western portion of the submarine Main Marmara Fault, which poses a high seismic risk due to its proximity to the Istanbul metropolitan region. Some of the largest earthquakes of the instrumental era (2019 M5.8 and 2025 M6.2) close to Istanbul nucleated at the eastern edge of this partially creeping segment.

In this study, we combine near-fault dense seismo-geodetic deployments, with deep-learning seismicity catalogs to investigate the role of aseismic deformation in driving the seismicity and controlling the source properties along those creeping segments of the NAFZ. At the Ismetpasa segment, we present the first evidence of significant microseismicity on and up to ~5km off the main NAFZ fault branch (mostly ML < 2) surrounding the creeping patches. This microseismicity is likely driven by the aseismic slip on the main fault plane. We interpret this seismic activity as the signature of a weak, damaged fault zone surrounding the tip of the ruptures of the M>7 1943 and 1944 events.

 In the Marmara region, we show a series of eastward propagating M>5 events and a gradual eastward unlocking of the Main Marmara Fault over the last ~15 years. Seismic activity progresses from creeping toward transitional segments and is currently arriving at the locked Princes Islands segment south of Istanbul, which has the potential to host a M~7 earthquake. These findings highlight the role of aseismic slip in modulating the available shear stress and elastic stored energy, which, in turn, control the nucleation and arrest of large ruptures. Our results also illustrate the importance of monitoring fault systems including multi-disciplinary instrumentation that enables capturing the entire frequency band from slow to fast slip. 

How to cite: Martínez-Garzón, P., Becker, D., Jolivet, R., Jara, J., Cakir, Z., Chen, X., Nunez-Jara, S., Kartal, R. F., Türker, E., Dresen, G., Ben-Zion, Y., Cotton, F., Kadirioglu, F. T., Kilic, T., and Bohnhoff, M.: Seismic potential of creeping segments of the North Anatolian Fault: insights from seismo-geodetic deployments and deep learning catalogs , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8784, https://doi.org/10.5194/egusphere-egu26-8784, 2026.

       The 2021 Mw 7.4 Maduo earthquake, rupturing within the Bayan Har block, provides a unique opportunity to investigate long-term postseismic deformation and lateral rheological heterogeneity of the lithosphere in northeastern Tibet. Here, we present four years (2021–2025) of postseismic deformation derived from continuous GNSS and InSAR observations to characterize the long-term deformation pattern and its underlying rheological controls. The GNSS and InSAR time series reveal a sustained growth of cumulative postseismic deformation, with both deformation amplitude and spatial extent progressively increasing with time. Maximum line-of-sight deformation inferred from InSAR reaches ~80 mm four years after the earthquake, consistent with the horizontal displacement magnitudes recorded by GNSS. The deformation exhibits a clear temporal transition, characterized by rapid growth during the first 1–2 years, followed by a substantially reduced but persistent deformation rate during years 3–4. During the later stage, localized regions exhibit additional deformation of up to ~5 mm, indicating that postseismic processes continue to operate over multi-year timescales. Modeling of the early postseismic deformation indicates that first-year displacements are jointly controlled by afterslip and viscoelastic relaxation, whereas the contribution from poroelastic rebound is negligible. Rheological inversion of the early postseismic deformation constrains optimal steady-state viscosities of 2–5 × 10¹⁹ Pa s for the lower crust and 3–10 × 10¹⁹ Pa s for the upper mantle, indicating the presence of a mechanically weak lower crust beneath the Bayan Har block. By incorporating the full four-year deformation time series, we further identify pronounced lateral variations in postseismic deformation behavior across the East Kunlun fault. South of the fault, the long-term deformation decay is broadly consistent with a weak lower crust characterized by viscosities on the order of ~10¹⁹ Pa s. In contrast, north of the fault, systematic spatial and temporal misfits between observations and homogeneous rheological models require a substantially stronger lower crust, with effective viscosities on the order of ~10²¹ Pa s. These results indicate that the East Kunlun fault represents a first-order rheological boundary separating laterally contrasting lithospheric domains in northeastern Tibet, and highlight the critical role of long-term GNSS and InSAR observations in resolving lateral rheological heterogeneity that cannot be captured by short-term postseismic data alone.

How to cite: Li, J., Chen, Y., Zhang, Z., Zhan, W., and Deng, Z.: Constraints on Lateral Rheological Heterogeneity in Northeastern Tibet from Long-Term GNSS and InSAR Observations following the 2021 Maduo Earthquake, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9031, https://doi.org/10.5194/egusphere-egu26-9031, 2026.

Satellite geodesy has become a powerful and reliable approach for investigating of geophysical processes, including tectonic, seismic, and volcanic activity. In seismotectonic research, the Global Navigation Satellite System (GNSS) provides precise estimates of plate motion parameters and offers valuable insights into present-day crustal deformation. The determination of Euler pole parameters and plate velocities represents a fundamental problem in global tectonics and a critical component of many geodynamic studies. This study aims to determine and analyze the parameters that characterize tectonic plate motion, specifically the rotation pole position (Φ, λ) and the angular rotation rate (Ω). The present-day kinematics of major tectonic plates are investigated using hundreds of geodetic observations provided by the Nevada Geodetic Laboratory (NGL) over the period 2000–2025. The analysis is based on GNSS station positions and velocities expressed in the International Terrestrial Reference Frame 2020 (ITRF2020). The estimation of Euler pole parameters for five major tectonic plates resulted in the following preliminary findings: for the African plate (𝜆𝐴𝑓=−81.97°±0.37; 𝜑𝐴𝑓=50.08°±0.14 and 𝛺𝐴𝑓=0.2665°𝑀𝑦𝑟⁄±0.0010);for the Eurasian plate (𝜆𝐸𝑢=−99.51°±0.98; 𝜑𝐸𝑢=54.61°±0.62 and 𝛺𝐸𝑢=0.2581°𝑀𝑦𝑟⁄±0.0016); for the North American plate (𝜆𝑁𝐴=−88.70°±0.32; 𝜑𝑁𝐴=−8.18°±0.42 and 𝛺𝑁𝐴=0.1863°𝑀𝑦𝑟⁄±0.0009 ); for South American plate (𝜆𝑆𝐴=−128.17°±0.92; 𝜑𝑆𝐴=−19.12°±0.35 and 𝛺𝑆𝐴=0.1178°𝑀𝑦𝑟⁄±0.0015) ; and for the Australian plate (𝜆𝐴𝑢=37.87°±0.22; 𝜑𝐴𝑢=32.84°±0.15 and 𝛺𝐴𝑢=0.6331°𝑀𝑦𝑟⁄±0.0007).The results were compared with the NNR-MORVEL56 plate motion model, providing key information for geodynamic modeling and insights into present-day tectonic behavior and seismic hazard.
Keywords
GNSS Stations; Tectonic Plates Velocities; Euler pole Parameters; ITRF2020.

How to cite: Allal, S. H., Hasni, K., and Dekkiche, H.: Recent Kinematics Analysis of Major Tectonic Plates from GNSS Positions and Velocities in the ITRF2020, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10128, https://doi.org/10.5194/egusphere-egu26-10128, 2026.

Steep relief and nearby ocean influenced weather patterns at Teide–Pico Viejo volcano create strong, elevation‑correlated tropospheric delays that can obscure millimetric ground motion in C‑band InSAR. We applied a robust workflow to isolate true deformation at Teide (2015–2025) by combining multi‑geometry Sentinel‑1 time series. Our pipeline integrates (i) ascending/descending TOPS stacks processed with SBAS method; (ii) numerical weather model corrections (e.g., ERA5‑based slant delays using PyAPS) to remove water‑vapor structure; and (iii) Common-mode filtering to minimize atmospheric residuals due a single deformation reference area (Mohammadnia et al., 2025). Finally, we recovered 3‑D deformation fields by combining information from 3 line‑of‑sight geometries. The atmospheric-corrected solutions substantially suppress topography‑correlated variance and reveal coherent, low‑amplitude deformation that otherwise would have been misinterpreted as larger magnitude volcanic deformation. The emergent pattern is dominated by slow, millimeters per year, deformation since 2022. Signals are superimposed with centimetric seasonal vertical signals. Our results demonstrate that rigorous atmospheric corrections are essential to recover sub-centimeter deformation spanning multiple years at high‑relief volcanoes to isolate magmatic-hydrothermal pressurization signals. 

References:
Mohammadnia, M., Yip, M.W., Webb, A.A.G., González, P.J. (2025) Spontaneous transient summit uplift at Taftan volcano (Makran subduction arc) imaged using an InSAR common-mode filtering method, Geophysical Research Letters, doi:10.1029/2025GL114853

Acknowledgements: We thank Spanish Agencia Estatal de Investigación project PID2022-139159NB-I00 (Volca-Motion) funded by MCIN/AEI/10.13039/501100011033 and “FEDER Una manera de hacer Europa”. 

How to cite: Gonzalez, P. J., Mohammadnia, M., Boulesteix, T., Webb, A. A. G., and Charco, M.: Atmospherically corrected deformation at a prominent‑topography volcano: Teide-Pico Viejo volcano, Tenerife, Canary Islands (2015–2025), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10208, https://doi.org/10.5194/egusphere-egu26-10208, 2026.

About 80% of shallow (depth < 60 km) earthquakes with Mw > 6.5 worldwide occur on offshore faults, highlighting the need for seafloor geodetic measurements to monitor strain accumulation before, during, and after major events. The current state-of-the-art technique for measuring horizontal seafloor deformation is GNSS/Acoustic (GNSS/A), which provides episodic measurements of absolute seafloor motion with centimeter-level precision at any depth. However, widespread application of GNSS/A remains limited by three main constraints: (1) high operational cost; (2) the inability to leave acoustic transponders in shallow waters (< 500 m) because of trawling activity; and (3) the need for long acquisition sessions to average out poorly modeled sound-speed variability in the water column. Here we present a new approach suitable for shallow water (< 300 m) that potentially enables centimeter-level seafloor geodesy at reduced cost and with shorter acquisition times. The method combines high-resolution optical imaging of the seafloor acquired by low-cost autonomous underwater vehicles (AUVs) with GNSS/A surveys. Acoustic beacons are used as ground control points, analogous to aerial photogrammetry, allowing georeferencing of the optical mosaics in a global reference frame. Natural markers such as rocks, reefs, and outcrops can then be re-imaged over time to measure displacement. Compared to classical GNSS/A, this approach uses acoustic beacons only during the survey, enabling multiple seafloor points to be monitored within a single experiment using a limited number of transponders. We will present results from a proof-of-concept experiment conducted in autumn 2025 near Toulon, southern France.

How to cite: Reveneau, H., Nocquet, J.-M., Royer, J.-Y., Furst, S., Varais, N., Verdun, J., Coulombier, T., Ballu, V., Eceiza, A., Sladen, A., and Sakic, P.: Hybrid Optical–GNSS/Acoustic Method for Centimeter-Precision Seafloor Geodesy in Shallow Water, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10362, https://doi.org/10.5194/egusphere-egu26-10362, 2026.

North-Eastern Italy is of particular interest in tectonics as it lies on the northernmost edge of the convergent margin between Eurasia and the Adria microplate, influencing regional deformation and seismicity. The Friuli Venezia Giulia Deformation Network (FReDNet) was established in the area in 2002 to monitor crustal deformation and contribute to regional seismic hazard assessment.

Tunini et al. (2024) described the time series spanning two decades from GNSS stations located in north-eastern Italy and surrounding areas, as well as the resulting velocity field in the ITRF14 reference frame. The documented dataset was obtained by processing GPS observations with GAMIT/GLOBK software version 10.71. The time series, estimated using the same procedure, are collected daily and stored as part of a long-term monitoring project, with annual updates of velocity solutions computed.

In this study, we present a multi-constellation solution and evaluate the differences compared to the GPS-only solution. We also update the solution to the new implementation of the International Terrestrial Reference Frame (ITRF2020). We then analyse the impact of the new reference system on the characteristics of the time series and the velocities. We also include additional stations that have recently become available in the solution.

We acknowledge the CINECA award under the ISCRA initiative, for the availability of high performance computing resources and support (IscraC IsCd5_MGNSS20).

Reference:

Tunini, L., Magrin, A., Rossi, G., and Zuliani, D.: Global Navigation Satellite System (GNSS) time series and velocities about a slowly convergent margin processed on high-performance computing (HPC) clusters: products and robustness evaluation, Earth Syst. Sci. Data, 16, 1083–1106, https://doi.org/10.5194/essd-16-1083-2024, 2024.

How to cite: Magrin, A., Tunini, L., Zuliani, D., and Rossi, G.: Adria-Eurasia collision front: Multi constellation GNSS data Processing in ITRF2020 reference frame, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11657, https://doi.org/10.5194/egusphere-egu26-11657, 2026.

The Cascadia subduction zone represents a seismic hazard to the Pacific Northwest region of North America, yet the state of fault locking near the deformation front, which could cause a devastating tsunami upon rupturing, remains poorly understood due to limited offshore observations along the subduction zone. In this study, we present the first seafloor geodetic measurements of the horizontal deformation rates on the accretionary prism from an array of four Global Navigation Satellite System-Acoustic (GNSS-Acoustic) sites surveyed from 2016-2022. These GNSS-Acoustic sites, despite resting on the North American plate, show velocities that are a significant fraction of the subducting Juan de Fuca plate velocity. In contrast, the continuous GNSS stations along the Oregon coast are moving at velocities <1 cm/yr relative to the North American Plate. Locking models constrained by these offshore velocities show that the subduction zone interface near the deformation front must be nearly locked offshore Oregon. To satisfy both the onshore and offshore geodetic observations, the locked zone must be relatively narrow and only minimal aseismic creep is permissible at the deformation front. These results suggest that appreciable elastic strain has accumulated near the deformation front, which elevates the potential for tsunamigenesis along this portion of the subduction zone.

How to cite: DeSanto, J., Schmidt, D., Zumberge, M., Sasagawa, G., and Chadwell, C. D.: Near full locking along the shallow megathrust of the Cascadia subdduction zone identified from seven years of GNSS-Acoustic observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11756, https://doi.org/10.5194/egusphere-egu26-11756, 2026.

Deformation measurements from space-borne Interferometric Synthetic Aperture Radar (InSAR) resolve geodynamic signals at multiple spatial scales and are commonly integrated with ground-based measurements from the Global Navigation Satellite System (GNSS). The integration process requires accounting for reference frame discrepancies and measurement uncertainties. In this study, we propose a new approach, CoInSAR, which uses least squares collocation to transform InSAR displacement time series into the GNSS reference frame while correcting residual tropospheric errors from turbulent atmospheric effects that typically persist in InSAR data. In our approach, we construct the observation vector at each epoch from the displacement differences between GNSS and InSAR, which comprises the reference frame difference, measurement noise, and residual tropospheric errors. We represent the measurement noise via data variances and derive the stochastic model for residual tropospheric errors using an empirical covariance function estimated from InSAR displacements. By accounting for these stochastic components, we use least squares collocation to estimate the transformation parameter between the two reference frames, interpolate corrections for the residual tropospheric errors, and generate the integrated displacements. To assess the performance of our method, we applied CoInSAR to measure land subsidence in the San Joaquin Valley, California, and seismic deformation in Chile. Our results show high agreement between GNSS and CoInSAR time series and variance reduction in regions outside the GNSS network. Moreover, CoInSAR-based deformation estimates are not only consistent with physics-based models but also capture small-scale deformation features, highlighting CoInSAR’s potential to improve the modeling of geodynamic signals in regions with sparse GNSS coverage.

How to cite: Wang, C.-Y., Gómez, D., and Figueroa, M.: A least squares collocation approach to integrate InSAR and GNSS observations: CoInSAR, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12697, https://doi.org/10.5194/egusphere-egu26-12697, 2026.

Margins between tectonic plates host most large earthquakes recorded in the lithosphere. Over periods of tens to hundreds of years, relative plate motions along portions of crustal seismogenic faults promote the slow accrual of stress (i.e., the inter-seismic stress gain) that is later suddenly released via earthquakes (i.e., the co-seismic stress drop) – a process generally referred to as seismic cycle. Virtually all models of seismic hazard assessment assume that whole-plate motions (i.e., motions that are adequately described via Euler vectors) remain steady over the seismic cycle, and that the impact of inter- and co-seismic stress variations is solely crustal deformation in the vicinity of seismogenic faults. From the standpoint of plate dynamics, however, plate-margin stress variations during the seismic cycle generate torques that may be comparable in magnitude to those associated with viscous stresses at the lithosphere/asthenosphere interface, which resist plate motions. On this basis, it is plausible to hypothesize that whole-plate motions may be susceptible to temporal variations over the seismic cycle. The availability of progressively longer and denser GNSS position time series measured at sites located inside several tectonic plates indeed favor testing such a hypothesis. Here I will show results from recent studies that analyze publicly available GNSS data and infer temporal variations of the motions of several tectonic plates. These changes appear consistent with the torque variations associated with inter- or co-seismic phases of large earthquakes occurred along their margins. I will speculate on whether the link between whole-plate motions and the seismic cycle is robust enough to draw any additional information in the context of models of seismic hazard assessment.

How to cite: Iaffaldano, G.: Testing whole-plate motion steadiness over the seismic cycle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12754, https://doi.org/10.5194/egusphere-egu26-12754, 2026.