EGU General Assembly 2023  

Current developments in quantum physics and the application of general relativity open up advanced prospects for satellite geodesy, gravimetric Earth observation and reference systems and thus strongly help to meeting the geodesy challenges in a unique way. As Vening-Meinsz advanced gravimetry 100 years ago with his pendulum apparatus, quantum optics can push it further using atoms today. These novel concepts include the application of atom interferometry for realizing quantum gravimetry and gradiometry, the enhanced use of laser interferometry for inter-satellite tracking and accelerometry at future gravity field missions, and relativistic geodesy with clocks for the determination of gravity potential differences via gravitational redshift measurements.

We briefly illustrate those novel techniques and present in which fields geodesy and geosciences will benefit from them. We show various application areas ranging from the direct determination of physical heights and the monitoring of mass variations using clock networks up to the use of quantum technology for gravimetric Earth observation on ground and in space. Realizing these innovative methods is key to quantify climate change processes (groundwater changes, ice mass loss, seal level rise, etc.) with largely increased precision and resolution.

Finally, we would like to mention the IAG project “Novel Sensors and Quantum Technology for Geodesy (QuGe)” that advances those activities in close collaboration between geodesy and physics, see https://quge.iag-aig.org/  -  see also: Van Camp, M., Pereira dos Santos, F., Murböck, M., Petit, G., Müller, J. (2021): Lasers and Ultracold Atoms for a Changing Earth. EOS, 102, https://doi.org/10.1029/2021EO210673

Acknowledgment: This study has been funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy EXC 2123 Quantum Frontiers - Project-ID 90837967 and the SFB 1464 TerraQ - Project-ID 434617780.

How to cite: Müller, J.: Benefit of Quantum Technology for Geodesy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5719, https://doi.org/10.5194/egusphere-egu23-5719, 2023.

Glacial isostatic adjustment (GIA) describes the response of the solid earth to ice mass changes and corresponding changes in the sea level. This process is visible in various geoscientific observations, with geodetic measurements being crucial to understand and describe the process. For example, the vertical and horizontal motion of the lithosphere is visible in GNSS (Global Navigation Satellite Systems) time series in the currently (Greenland, Antarctica, Svalbard) and formerly glaciated regions (North America, northern Europe). In addition to geodetic observations of GIA, the solid earth deformation is visible in various geological data. The vertical motion of the lithosphere can be seen in relative sea level and lake level data, but for a different epoch then GNSS data. All these observations help to explain GIA as well as infer the structure of the Earth via so-called GIA models. GIA models can be constrained by geodetic and geological observations and in turn can help to predict these observations. An essential component of GIA models is knowledge about the distribution of material parameters of the Earth’s lithosphere and mantle. This can be obtained from various geophysical measurements (e.g., gravity, seismology).

Here, I will show how we can infer the depth of various material layers in the lithosphere from geodetic data exemplary for Greenland and how we can use these in three-dimensional GIA models. I will also discuss the effect of various lithosphere models on the modelled GNSS velocities.

How to cite: Steffen, R.: Geodesy meets tectonophysics: Advancing our estimates of glacial isostatic adjustment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11261, https://doi.org/10.5194/egusphere-egu23-11261, 2023.

The modernized GNSS transmit more signals on various frequencies to suit different application scenarios. However, for a long time, ambiguity resolution has been available to PPP users only on a few signal frequencies specified by the PPP service provider, which prevents other signal frequencies from being used for high-precision positioning applications. Recently, the GNSS Research Center of Wuhan University offered a new version of open-source PRIDE PPP-AR software and a set of “all-frequency” PPP-AR products, that supports PPP users in achieving undifferenced ambiguity resolution on any dual-frequency ionosphere-free combination based on the same satellite phase clocks. The new feature of PRIDE PPP-AR was tested with GPS/Galileo/BDS observations from 200 multi-frequency IGS stations in the first 9 months of 2022. The mean wide-/narrow-lane ambiguity fixing rates can achieve 90% on most of the common dual-frequency combinations, including GPS L1/L2, the combination of Galileo E1 and Galileo E5a/E5/E5b/E6, and BDS-3 B1C/B2a and B1I/B2I. On the other common dual-frequency combinations except for the BDS-2 B1I/B2I, the mean wide-/narrow-lane ambiguity fixing rates can achieve 80%. On all the above dual-frequency combinations, the positioning RMS errors compared with the IGS weekly solutions are about 2 mm in the east and the north directions, and below 7 mm in the high direction. Additionally, the new version of PRIDE PPP-AR enables precise orbit determination for LEO satellites. The TurboEdit algorithm was improved with forward and backward moving window averaging (FBMWA) method to accommodate the need for achieving ambiguity resolution on fast motion objects. A comparison between the computed orbits and JPL’s precise orbits for GRACE-FO in 2019 shows that the 3D RMS difference is within 1.7 cm. The PRIDE PPP-AR was first released in 2019 and dedicated to expanding the scope of PPP-AR in geodetic researches. After several updates, this GNSS analysis tool now supports multi-day continuous processing, processing of very-high-rate GNSS data, and quasi-real-time processing with real-time archived PPP products. With the new features of all-frequency PPP-AR and PPP-AR on LEO satellites, the new version of PRIDE PPP-AR will be able to take full advantage of GNSS modernization to improve high-precision positioning accuracy in more research areas.

How to cite: Geng, J., Lin, J., Zeng, J., Li, W., and Zhang, Q.: PRIDE PPP-AR: an open-source scientific software with all-frequency PPP ambiguity resolution for geodesy, geophysics and photogrammetry applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2162, https://doi.org/10.5194/egusphere-egu23-2162, 2023.

A MATLAB toolbox, also compatible with GNU Octave, was developed in order to allow a user not necessarily expert in programming to calculate the strain rate field of an area by means of a procedure with a high level of automation starting from coordinate time series. The results can be used to investigate the crustal tectonic deformations of the studied area. These steps are implemented:

• time series download from a data repository, e.g. the Nevada Geodetic Laboratory (NGL), or another similar database (the download function can be easily edited to allow the use of input time series having different format);
• calculation of the station velocities by means of the Maximum Likelihood Estimation (MLE) method, including modeling of offsets, outliers, noise and periodic components. The MLE modeling is carried out by using the external package Hector (Bos et al., 2013. J. Geod., 87, 351-360), automatically called by means of a specifically developed MATLAB function;
• estimation of Common Mode Error and, if necessary, its removal from time series of some stations and recalculation of the corresponding velocities.
• calculation of the strain rate field on a regular grid with the modified least squares method, in which a scale factor can be introduced to define the locality of the deformation analysis. Besides the strain rate field, the toolbox provides the corresponding uncertainty estimation and geometric evaluation of the significance of the results;
• visualization of the results for their interpretation for scientific purposes, including the map of principal strain and the contour plots of change in area (or dilatation), engineering shear normalized to the change in area, second invariant of the strain, prevailing eigenvalue, corresponding uncertainties and geometric significance.

The toolbox, which is available free of charge to any interested user, is characterized by considerable flexibility, and can be easily adapted to different data sources.

The toolbox was recently used in order to refine the rates of active crustal deformation in the upper plate of subduction zones in the specific case of the E-dipping West Crati fault (Calabria) and to evaluate the convergence rate in the Main Thrust Fault (also called Sicilian Basal Thrust) north to Hyblean Plateau (South-Eastern Sicily). 

How to cite: Teza, G., Pesci, A., and Meschis, M.: A MATLAB/GNU Octave toolbox for computation of velocity and strain rate field from GNSS coordinate time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2453, https://doi.org/10.5194/egusphere-egu23-2453, 2023.

In GNSS analysis, tropospheric modelling is done in the form of Zenith Hydrostatic Delay (ZHD), which can be empirically computed from surface pressure and temperature, and Zenith Wet Delay (ZWD), which is estimated together with the other unknown parameters.  Analysis methods based on undifferenced GNSS code- and carrier-phase observations like Precise Point Positioning (PPP), which can achieve millimeter-accurate positioning results, provide therefore also time-series of ZWD, which can be used for meteorologic applications. However, due to receiver noise and system characteristics like cycle-slips the accuracy as well as the precision of such ZWD estimates is limited. Thus, we propose a novel approach for sites, which have several receivers connected to a single antenna or which are separated horizontally by only a few meters. For such sites, one can simultaneously process multi-frequency GNSS data by fusing observations from several receivers, while estimating a common ZWD parameter.

For this purpose, we have implemented a PPP algorithm based on an Extended Kalman Filter (EKF) approach, which has the advantage that ZWD estimates are available in real-time for meteorologic applications. We demonstrate that those combined ZWD estimates are superior to single receiver estimates in term of precision and accuracy. For the latter measure, we make use of a GNSS hardware simulator and show that the RMS between the simulated and estimated ZWD significantly decreases when having two or more receivers at that site. Based on real-data we show that this concept provides less noisy ZWD estimates which agree better with physical properties of the local wet refractivity field.

Moreover, we demonstrate that fusing data from several receivers by estimating a common ZWD parameter improves also positioning accuracy and precision, in particular in the up-component. In order to properly combine observations from geodetic-grade and low-cost GNSS receivers, we present our adaptive Kalman filter approach, which adjusts the observation noise covariance matrix automatically during processing. The presentation concludes with an outlook on the usage of this approach for larger networks and answers the question how arrays of low-cost GNSS receivers can compete against geodetic-grade GNSS hardware in term of providing ZWD estimates for meteorology.

How to cite: Wang, R., Hobiger, T., Marut, G., and Hadas, T.: Improving GNSS meteorology by fusing measurements of multi-receiver sites on the observation level, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3364, https://doi.org/10.5194/egusphere-egu23-3364, 2023.

Due to the correlation between coordinates, atmospheric delays, and ambiguities, Precise Point Position with Ambiguity Resolution (PPP-AR) needs a long convergence time (around 20 min) to achieve cm-level accuracy. With the help of precise external atmospheric products, PPP-AR convergence time can be reduced to a few minutes or even instantaneously. However, a stable and continuous data transmission in real-time communication could be challenging in more expansive areas due to the massive amount of correction information from dense networks. In addition, data interruptions and switching reference stations also could cause discontinuity or anomalies in the real-time correction information. By combining both wide-area fitting functions and regional un-modeled corrections, we present an integrated hierarchical augmentation method, which could ensure reliable and precise positioning with less communication burden. The first level of the hierarchical model includes the satellite-wise slant ionospheric delay and tropospheric Zenith Wet Delay (ZWD) wide-area fitting models, which provides an essential correction with few model coefficients covering a larger area. Moreover, the residual unmodeled errors and phase residuals can be provided optionally, according to the communication capability and the user’s requirement. The newly developed augmentation mode extends from the current wide-area low-precision to the hierarchical-precision service, which relieves the communication burden and greatly reduces the dependence on the distribution of reference stations. We evaluate our model in the European region, using 103 EUREF Permanent Network (EPN) stations with 200 km station-spacing as modeling stations and 84 stations as external validation. The precision of the wide-area ionospheric and tropospheric delay models are 4.5 cm and 1.3 cm, respectively. With only the wide-area correction information, an convergence time (to 10 cm) of 2 and 3 minutes can be achieved for the horizontal and vertical components, respectively. Based on the magnitude of wide-area unmodeled errors, the optional unmodeled correction broadcast volume can be saved by 40-50% with respect to the legacy interpolation mode. Moreover, instantaneous ambiguity fixing within one to two epochs (1 min) can be achieved if the unmodeled residuals are exploited. Therefore, the proposed hierarchical augmentation mode satisfies different positioning demands of wide-area with low resource utilization.

How to cite: Cui, B., Wang, J., Jiang, X., Li, P., Ge, M., and Schuh, H.: An integrated hierarchical wide-area augmentation for real-time GNSS positioning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3580, https://doi.org/10.5194/egusphere-egu23-3580, 2023.

We present in this contribution the main aspects of efforts done at the CNES/CLS Analysis Center in 2022-2023. We recall the main changes associated with the adoption of the IG20/IGS20.atx standards relying on the recently released International Terrestrial Reference Frame (ITRF2020) and following our participation to the third IGS reprocessing campaign (REPRO3).  We also increased our participation to IGS with the delivering of rapid and ultra-rapid products: the quality and specificities of these products (orbit, clocks and erp) are presented together with their availability and some details on the associated processing chain. Finally, we focus on the preliminary results of the processing of the satellites of the Beidou constellation that will be included soon in our products.

How to cite: Loyer, S., Mezerette, A., Saquet, E., Baños-Garcia, A., Santamaria Gomez, A., Mercier, F., and Perosanz, F.: CNES/CLS IGS Analysis Center 2022/2023 Activities, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5308, https://doi.org/10.5194/egusphere-egu23-5308, 2023.

Global navigation satellite systems (GNSS) products are integral to a wide array of scientific and commercial applications such as pecise orbit determination of low Earth orbit satellites, earthquake monitoring, GNSS reflectomrety, tropospheric and ionospheric research, surveying and much more. These products consisting of GNSS orbit, clock, phase biases and more are generated by the analysis centres of the International GNSS Service (IGS) by processing observations from a global network of ground stations to one or more GNSS constellations. The processing consists of a combined station position and GNSS satellite orbit determination through a least squares approach donated as global multi-GNSS processing.

Within global multi-GNSS processing it is assumed that the observation noise is elevation-dependent and any spatial and temporal correlations are disregarded. Within numerous studies it has been shown that this assumption is incorrect while several studies additional pointed out that a sophisticated stochastic modelling has a positiv impact on GNSS processing and resulting products. In past reseach we have shown to exploit the post-fit residuals to derive temporal correlations for a sophisticated stochastic modeling. However, there have not been any large-scale investigations regarding the impact of stochastic modelling of observation noise on global GNSS processing products. Furthermore, to guarantee the quality of the GNSS products global multi-GNSS processing requires a sophisticated cycle slip detection and repairing algorithm. Cycle slips are discontinuities in the phase observations and if not corrected can lead to degrading quality of GNSS products.   

We present our advancements in global multi-GNSS processing by exploiting post-fit residuals for stochastic modeling and cycle slip detection. We used several years of observations and a selected IGS network of ground stations to generate GNSS products. Based on this data we analysed the impact our newly integrated approaches have on GNSS products such as orbits, clocks, phase biases and station coordinate time series.  

How to cite: Dumitraschkewitz, P., Mayer-Gürr, T., Suesser-Rechberger, B., and Öhlinger, F.: Exploitation of post-fit residuals in global GNSS network processing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5582, https://doi.org/10.5194/egusphere-egu23-5582, 2023.

In recent years, there has been a significant advancement in the field of Global Navigation Satellite Systems (GNSS). The completion of newly built systems (Galileo, BeiDou) together with the modernisation of long-standing systems (GPS, GLONASS) has brought new signals and also new services to users. A significant technological advance has also been achieved in the development and availability of low-cost devices enabling positioning and navigation based on GNSS alone or a combination of several technologies. The study focuses on testing GNSS receivers in smartphones and low-cost devices combining GNSS and inertial navigation. The aim was to address the current capabilities and the quality of positioning offered by these devices. The analyses were performed on test measurements performed in kinematic mode in an urban environment at walking speed. The aim was to make test measurements that are representative enough to reflect conditions commonly encountered in life. Advanced GNSS techniques were tested in both real-time and post-processing of the raw observations. Low-cost u-blox single and multi-frequency modules combining GNSS and inertial localization, as well as standard Samsung mobile phones were used. Impact of the GNSS (multi-)constellation on the quality of positioning was also evaluated, as some GNSS signals exhibit higher multipath resistance and a higher number of satellites can significantly help with positioning initialization and improve its accuracy.

How to cite: Halaj, M. and Kacmarik, M.: Performance of Low-cost GNSS/INS Receivers and Smartphone GNSS Positioning in Pedestrian Applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5850, https://doi.org/10.5194/egusphere-egu23-5850, 2023.

GPS III is the latest generation of modernized satellites of the Global Positioning System. Five GPS III satellites have already been launched between December 2018 and June 2021 and three further GPS III spacecraft are available for launch. Starting in 2019, satellite antenna phase center offsets (PCOs) for the L1, L2, and L5 frequency bands have been published by the manufacturer Lockheed Martin for the individual spacecraft launched so far. These PCOs are included in the igs20.atx antenna phase center model of the International GNSS Service (IGS). They are complemented by nadir-dependent phase center variations (PCVs) estimated by the Center for Orbit Determination in Europe (CODE) and the European Space Operations Center (ESOC). In Fall 2022, manufacturer-calibrated nadir- and azimuth-dependent directivity and phase patterns were, furthermore made available, which provide a more complete description of the antenna characteristics.

This contribution aims at a validation of these satellite antenna metadata. As a reference, satellite antenna PCOs and PCVs are estimated from L1/L2 and L1/L5 ionosphere-free linear combinations of a global network of GNSS tracking stations. These are compared to the ground calibrations of the GPS III transmit antennas obtained in an anechoic chamber. The manufacturer-provided directivity patterns for the main lobe of the GPS III transmit antennas can be validated with observations of a directional high-gain antenna. The 30 m dish antenna of the German Aerospace Center (DLR) located in Weilheim, Germany, was used to obtain equivalent isotropic radiated power (EIRP) measurements of all GPS III spacecraft. Repeated measurements are used to evaluate the measurement precision and elevation-dependent RMS differences allow for an assessment of the consistency of the EIRP measurements and the pre-flight gain calibrations.

How to cite: Steigenberger, P., Thoelert, S., Dach, R., and Montenbruck, O.: Validation of GPS III antenna patterns, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6769, https://doi.org/10.5194/egusphere-egu23-6769, 2023.

As the Cordouan lighthouse [N45°35'11"; W1°10'24"] is constructed in the Bay of Biscay, GNSS reflectometry-monitored time series of sea level are characterized by important tidal variations for this site. However, these GNSS-R measurements are impacted by submerged sandy banks that appear at low tide and spoil the estimates of pure sea level. We propose the spatialization of the GNSS reflection points to identify the areas with sandy or rocky parts around the lighthouse. For this purpose, the surrounding of the receiving antenna is divided into juxtaposed geographical cells forming a map filled by water heights estimates according to the position of the reflection points. Water heights are determined using the method of periodogram of 1-second Signal-to-Noise-Ratio (SNR) data on a sliding elevation window of several degrees. In particular, correction of the atmospheric delay effects enables to reduce the dispersion of the water heights versus low elevations by a factor around 2. High variability (more than one meter) and higher means of water heights estimated over months in the eastern part are very consistent with the presence of the shoals, while long-term means and dispersions in cells of plain ocean are much smaller. These results are highly emphasized by the distinction between low and high tides.

How to cite: Gravalon, T., Seoane, L., Ramillien, G., and Darrozes, J.: Spatialization and analysis of the GNSS-R measurements around of the Cordouan lighthouse, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7957, https://doi.org/10.5194/egusphere-egu23-7957, 2023.

How to cite: Seoane, L., Gravalon, T., Ramillien, G., and Darrozes, J.: Methodological improvements for deriving long-term time series of coastal sea level by GNSS-R, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8828, https://doi.org/10.5194/egusphere-egu23-8828, 2023.

Fast magnitude estimation of large earthquakes has been a key task for warning systems. In the last decades, Global Navigation Satellite Systems data with high-rate sampling (≥1 Hz; HR-GNSS) have provided us with useful information from displacement time series for analyzing large earthquakes; especially when the signals of earthquakes recorded in inertial sensors are saturated. Hence, improving algorithms to contribute to the fast analyses of the HR-GNSS data has been a recent challenge.

In this work, we propose a deep-learning-based algorithm for earthquake magnitude estimation, which was trained by thousands of synthetic displacement time series corresponding to Mw > 6.5 earthquake signals. We adapted the model to a variable number of stations and lengths of the time series as input. Thus, it is possible to apply the algorithm without any restriction on the number of stations, and the flexibility in the length of the input time series facilitates the inclusion of data not only from local stations but also from regional stations if required. The influence of attributes such as noise, magnitude, number of stations, epicentral distance, and length of input time series on the model performance was evaluated. We aim to generalize this approach to the magnitude estimation of earthquakes from different tectonic regions. The robustness of the model was tested with both synthetic and real earthquake signals.

How to cite: Quinteros-Cartaya, C., Köhler, J., Faber, J., Li, W., and Srivastava, N.: Fast Earthquake Magnitude Estimation using HR-GNSS time series: a Deep Learning approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9248, https://doi.org/10.5194/egusphere-egu23-9248, 2023.

Ionospheric disturbances can negatively impact the accuracy, continuity, availability, and integrity of Global Navigation Satellite Systems (GNSS) based services. Therefore, reliable description and characterization of these disturbances are essential to guarantee an adequate level of safety for GNSS-based systems, susceptible to strong spatial gradients and rapid changes in electron density along the receiver-satellite path (slant total electron content, STEC).

This study aims to compare various indices that describe the current condition and intensity of ionospheric disturbances using GNSS observations from approximately 350 reference stations in Europe. The indices studied include the Gradient Ionospheric Index (GIX), the Sudden Ionospheric Disturbance Index (SIDX), and the Rate Of Tec Index (ROTI). The study focuses on selected geomagnetic storms and compares the results for different latitude zones (30-45°N, 45-60°N, and 60-75°N). The results show that the behaviors of the investigated indices differ in each case and are strongly dependent on the ionospheric storm propagation mechanism and associated with actual space weather and geo-physical conditions. The study also examines the relationships between the analyzed indices and GNSS positioning results using absolute and differential approaches and code pseudorange and carrier phase-based results. In addition, a comparison with vertical protection error (VPE) and vertical protection level (VPL) for selected EGNOS Ranging and Integrity Monitoring Stations is included.

How to cite: Nykiel, G., Cahuasquí, J. A., Hoque, M., and Jakowski, N.: Comparison of GIX, SIDX and ROTI ionospheric indices and their relationships with GNSS positioning results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9450, https://doi.org/10.5194/egusphere-egu23-9450, 2023.

A GNSS data set was recorded for ionosphere sounding on the German research icebreaker Polarstern during the expedition of MOSAiC (Multidisciplinary Observatory for the Study of the Arctic Climate). The GNSS setup comprised a multi-GNSS high-rate (50 Hz) receiver and a multiband GNSS antenna at right-handed polarization. During the one-year expedition (Sep. 2019 to Oct. 2020) the ship drifted with ice floes over the Arctic Ocean for studying the Arctic climate. In addition, the drift gave an excellent opportunity to collect GNSS data for ionosphere sounding over the central Arctic (at lat. > 85° N). More than five months the ship was drifting in the central part of the Arctic where data from permanent GNSS stations are not available. Nearest stations are all located further south. These measurements aboard Polarstern provide ideal conditions to study scintillations induced by disturbances in the Arctic ionosphere (e.g. by polar patches). The coincidence of the expedition period (2019/20) and solar minimum is a small drawback for the study. It limits the probability of strong scintillations in the observations. So, the question arises whether the precision of GNSS phase measurements on a ship is high enough to detect phase scintillations at solar minimum.

The standard deviation of detrended phase samples (phase scintillation index) is derived with 30 s resolution for each GNSS link to quantify disturbance. The study focuses in a first approach on GPS data and high elevation angles (> 30°) as these rays propagate rather vertically and stay in the central Arctic with ionospheric piercing points (assumed at 350 km) not far from the ship location (roughly: horizontal distance < 600 km). Three categories of disturbance are identified in this elevation range:

• Phase index baseline of about 0.1 +/- 0.05 rad, that is the lower limit for this ship-based setup
• Phase index anomalies from 0.15 to 0.4 rad (and more) that are found in constant directions on the ship (constant relative bearing) and can be attributed to disturbance of ship multipath/shadowing (by mast and chimney) affecting the field-of-view in these directions
• Phase index anomalies between 0.15 and 0.2 rad, that occur around local noon at the given high latitudes and can be identified as weak scintillations due to ionospheric disturbance in the cusp region (at the convergence of geomagnetic field lines)

Compared to a typical ground-based station operating in the Arctic, the ship-based measurements present a rather high baseline index level that is already in the weak scintillation range. The difference between baseline and the cusp-related scintillations is rather small. Parameters (latitude, elevation angle and local time of the observation) are considered to identify the ionospheric scintillations. Furthermore, anomalies induced by ship multipath disturb the scintillation detection and need to be identified and masked out based on relative bearing limits. We conclude that ship-based GNSS is precise enough to detect Arctic phase scintillations even at the minimum of the solar cycle if proper analysis is conducted.

How to cite: Semmling, M., Berdermann, J., Sato, H., Fohlmeister, F., Kriegel, M., and Hoque, M.: Are ship-based GNSS measurements precise enough to detect ionospheric phase scintillation at solar minimum?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9866, https://doi.org/10.5194/egusphere-egu23-9866, 2023.

Determining the accuracy of position and velocity using GNSS is now on the agenda of the research community. Each unique system in the GNSS puts effort to complete its constellation of satellites, with orbits and clocks of ever-increasing quality. In order to interpret the quality of the results, we started the IGS MGEX experiment, where we, as end users, used the network and its data for evaluation. Various software has been developed to evaluate Multi-GNSS products, and researchers evaluate the results of both independent and combined systems within the framework of their experiments and have the opportunity to compare the software with each other. Succeeding JPL's 2019 experiment, we focused on the evaluation of the GIPSY-X, a multi-GNSS software, positioning results and we would like to share our initial findings with you. Unlike other studies, our focus is on the factors influencing position determination and their mathematical modeling. There is also an emphasis in our study on the campaign Multi-GNSS. In the first part of the study, we made inferences about GPS+GLONASS positioning accuracy. We modeled and compared the results of CSRS-PPP and GIPSY-X with each other. In the second part, we examined the GALILEO contribution to the GIPSY-X positioning solutions, and again we present modeling. We still see the effect of the observation session on positioning on all results and modeled it for GPS+GLONASS+GALILEO. We could not see the "geographical latitude dependence" on positioning that we noticed in the GPS-only studies in these first trials. In this presentation, we will try to examine the possible reasons for this.

How to cite: Sanli, D. U., Cetin, D., and Ogutcu, S. S.: Multi-GNSS trials: a note on software comparison and campaign GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10853, https://doi.org/10.5194/egusphere-egu23-10853, 2023.

The high-rate GNSS has been proven to be an effective tool to describe moderate and strong natural earthquakes, whereas the much less addressed application is monitoring anthropogenic earthquakes, such as mining tremors, where the noise and displacements have similar values. Although the anthropogenic events have small magnitudes (usually below 4.5), they also have much shallower epicentres (depths up to 1-2 km). Therefore, the vibrations they cause are often felt and may have a dangerous impact on the ground, structures and infrastructure nearby.

Here we show that with the high-rate multi-constellation GNSS observations (GPS+Galileo), we can reliably detect the low-magnitude shallow anthropogenic earthquakes and characterise them in terms of displacements and velocities. Our filtering procedure is based on multiresolution analysis and successfully retrieves the small signal of ground vibrations. We analysed five mining tremors with magnitudes of 3.4-4.0 and presented the results from high-rate GNSS position changes calculated parallel with the PPP and variometric approach. The accuracy was very few millimetres for displacements and 1-2 cm/s for velocities. We obtained satisfying correlations with seismological data in correlation, peak values comparison and earthquake first epoch determination. Finally, considering the high-rate GNSS positioning noise level, we demonstrate the capacity to resolve the dynamic displacements from high-rate GNSS at the epicentral distance of about 7-8 km.

How to cite: Kudłacik, I., Kapłon, J., Fortunato, M., Kaźmierski, K., and Crespi, M.: GNSS-seismology for anthropogenic earthquakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11547, https://doi.org/10.5194/egusphere-egu23-11547, 2023.

Over the past decades, Precise Point Positioning (PPP) has become a well-established technique for determining the user's position with the signals of Global Navigation Satellite Systems (GNSS). PPP is characterized by applying precise satellite products (orbits, clocks, and biases) and accurately modeling a wide range of error sources to estimate the user's position. This way, a position accuracy at the centimeter or even millimeter level is accomplished. However, the convergence time until the coordinates have reached this accuracy is well known as the primary concern of PPP. In that regard, PPP with integer ambiguity resolution (PPP-AR) has proven as an effective way to dramatically reduce the convergence time of PPP, especially in the east coordinate component.

Currently, the so-called Orbit Exchange (ORBEX) format is under revision. Its main philosophy is larger flexibility for the description of the satellite state than in different existing formats. Besides other advantages, the ORBEX format can provide information on the satellite orientation in attitude records. Several Analysis Centers have started to provide such data in addition to their satellite orbits, clocks, and biases. Consequently, the PPP user can accurately calculate the satellite orientation instead of relying on the usually adopted IGS convention.

Since the satellites' orientation is essential for accurately modeling several error sources and recovering the integer property of the phase ambiguities, the performance of PPP is usually improved by using accurate satellite attitude information. This contribution illustrates the effect of attitude data on ambiguity fixing, convergence time (time to first fix), and coordinate accuracy in several test cases. Especially, satellite eclipse seasons are investigated. The PPP calculations are performed with our software raPPPid, the PPP module of the Vienna VLBI and Satellite Software (VieVS PPP).

How to cite: Glaner, M. F. and Weber, R.: Enhancing PPP-AR with satellite attitude data from ORBEX files, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11735, https://doi.org/10.5194/egusphere-egu23-11735, 2023.

In this study, we investigate the impact of GNSS antenna calibration models and multi-GNSS observations on the quality of the tropospheric estimates. The accuracy and homogeneity of the Zenith Total Delay (ZTD) time series estimated from ground-based GNSS data strongly depend on the processing strategy. These factors significantly imply the GNSS solution performance; however, their impact on the quality of the derived ZTD series used for climate applications has not been comprehensively investigated.

We analyzed three years of ZTD time series obtained from GNSS data processing and afterward converted integrated water vapor (IWV). Nine different processing strategies distinguished into three groups were employed: the 1st group of solutions was obtained by applying the International GNSS Service (IGS) type mean Phase Center Correction (PCC) models (IGS14); in the 2nd group, PCC models from individual field robot calibration were used; in the 3rd group of solutions, an anechoic chamber calibration was applied. Each group of solutions was processed three times using different GNSS constellations, namely GPS-only, Galileo-only, or combined GPS+Galileo.

The results reveal that the impact of employed GNSS constellations on the accuracy of the ZTD time series is more pronounced than the impact of antenna calibration models. However, the latter factor is also noticeable and thus cannot be neglected. Moreover, validation against climate reanalysis data confirms that all approaches provide high-quality tropospheric delays.

The outcomes also indicate that ZTD estimates obtained with robotic and IGS14 calibrations are closer to that of ERA5 reanalysis than estimates derived when using calibrations in an anechoic chamber. In addition, multi-GNSS-derived tropospheric parameters are more comparable to the benchmark ones from ERA5 than those provided by single-system solutions. The results also depend, among others, on the stations' equipment (receiver and antenna).

How to cite: Stępniak, K., Krzan, G., and Paziewski, J.: Impact of individual antenna phase center models and multi-GNSS observations on tropospheric estimates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15009, https://doi.org/10.5194/egusphere-egu23-15009, 2023.

GNSS/A is a proven method to localize seafloor geodetic stations and, thus, to monitor seafloor tectonic phenomena. This approach combines GNSS positioning of a surface platform with acoustic ranging between this platform and acoustic beacons on the sea bottom, with the objective to localize the beacons in a global frame within a centimeter or so. As part of the FOCUS project, a network of seafloor stations was deployed offshore Sicily in Italy, at about 1900 meters depth. It was surveyed from a small autonomous surface vehicle (ASV) equipped with two GNSS receivers. Here we present the post-processing applied to the GNSS surface navigation data in order to reduce the uncertainty budget of the GNSS/A algorithm. We found significant discrepancies between GNSS receivers in terms of signal degrading effects (multipaths, cycle slips, signal interruptions). We also found that GNSS antennas are less subject to these effects when mounted on an ASV rather than on the main vessel mast. The correlation found between solution accuracy and signal degrading effects potency turned out to be inadequate to predict the former knowing the latter. Then, we compared the accuracy of kinematic solutions from three GNSS PPP-AR post-processing packages to a few/several centimeters level. From our analysis, we find that the best accuracy was reached using the CSRS-PPP service.

How to cite: Lenhof, E., Royer, J.-Y., Ballu, V., Sakic, P., Poitou, C., Beauverger, M., Coulombier, T., Dausse, D., Jamieson, G., Morvan, P.-Y., and Gutscher, M.-A.: Comparison of GNSS PPP-AR packages for post-processing seafloor geodetic data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15254, https://doi.org/10.5194/egusphere-egu23-15254, 2023.

BeiDou Global Navigation Satellite System (BDS-3) was formally commissioned to provide satellite navigation services worldwide in 2020. It not only has the normal positioning, navigation and timing (PNT) functions, but also provides several kinds of featured services. The paper  focuses on the featured services of BDS-3 and their applications in various geoscience fields. First, the featured services of BDS-3 and their performances are introduced. Then different application examples are described and analyzed based on the Geostationary Orbit (GEO) satellite-based featured services and Middle Earth Orbit (MEO) satellite-based featured services. Finally, some possible improvements to BDS in the future are discussed.

How to cite: Yang, Y., Ren, X., Xu, T., and Sun, B.: Featured Services of BDS-3 with Applications in Geoscience, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17041, https://doi.org/10.5194/egusphere-egu23-17041, 2023.

In this study, a method is developed which allows to reduce the leakage effect in GRACE gravity fields The leakage effect means that mass changes are falsely assigned to nearby regions due to the limited resolution of the gravity field. These assignments are partly physically unreasonable.

In our method, we separate the entire Earth’s surface according to their surface type as e.g. sea and land surface. Across these regions, individual basis functions (e.g. Slepian functions) are applied. In a constrained least squares adjustment, a priori surface mass trends are rearranged to the respective regions while the basis functions’ coefficients are constrained differently according to their surface type. Therefore, we assume different variabilities of possible mass change. With the inclusion of a filter matrix, the resulting field of surface mass changes is linked to the a priori distribution which results directly from the input gravity field.

The procedure is tested for unfiltered and DDK-filtered GRACE gravity fields as well as SLR-based gravity fields.  Furthermore, geometric information on the changing sea level is introduced in order to improve the de-leakaging and de-aliasing of the input GRACE distributions of surface mass change. For this purpose, products of ESA’s marine service are applied. In our study, we want to show benefits and applications concerning ice mass estimation.

How to cite: Graf, M., Schlaak, M., and Pail, R.: De-Leakaging and De-Aliasing of GRACE-based Surface Mass Distributions by Regularized Basis Functions and Additional Geometric Information, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1005, https://doi.org/10.5194/egusphere-egu23-1005, 2023.

The Cyclone Global Navigation Satellite System (CyGNSS) is a constellation of eight microsatellites launched in 2016 with the goal of measuring global ocean wind speed. With four channels on each satellite, it produces up to 32 Delay Doppler maps (DDMs) per second. CyGNSSnet [1] is a machine learning algorithm developed to predict ocean surface wind speed directly from DDMs. Evaluated on an independent test set, CyGNSSnet achieved an RMSE of 1.36 m/s. It is however unknown whether the algorithm’s performance is stable, the further the evaluation date is from the training data range.

New DDMs are provided every day through the NASA EarthData cloud [2]. Here, we present an automatic machine learning pipeline to evaluate CyGNSSnet continuously using Prefect, a Python library for workflow orchestration. This allows us to schedule the pipeline daily and to handle the process smoothly in case of any failures. 

The workflow of the pipeline is as follows: the CyGNSS data and the ERA5 windspeed labels are downloaded and pre-processed. Wind speed predictions are made with the pretrained CyGNSSnet. Metrics of the model, including root mean squared error and bias, as well as visualizations are stored in a MongoDB database. All saved data can be accessed through a website, where users can analyze the current performance of CyGNSSnet and access previous visualizations and results.

The pipeline can be set up system-independent via Docker compose. It can easily be adapted to other remote sensing data sources and machine learning algorithms, provides a valuable software tool to leverage big data in remote sensing, and enables continuous validation of machine learning algorithms. In our contribution, we will demonstrate the performance of CyGNSSnet for the months leading up to the conference.

[1]  Asgarimehr, M., Arnold, C., Weigel, T., Ruf, C., Wickert, J. (2022): GNSS reflectometry global ocean wind speed using deep learning: Development and assessment of CyGNSSnet. - Remote Sensing of Environment, 269, 112801.

[2] CYGNSS. CYGNSS Level 2 Science Data Record Version 3.1. Ver. 3.1. PO.DAAC, CA, USA. accessed 2022/2023 at 10.5067/CYGNS-L2X31

How to cite: Grover, H., Albrecht, F., and Arnold, C.: Towards an operational CyGNSSnet - automated ocean wind speed prediction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1475, https://doi.org/10.5194/egusphere-egu23-1475, 2023.

Radio signals sent by Global Navigation Satellite System (GNSS) satellites are received by GNSS stations on Earth. The signals get delayed as they propagate through the troposphere, this delay can be measured and thus, tropospheric properties can be estimated.

The total tropospheric delay in zenith direction is split into a zenith hydrostatic delay (ZHD) and a zenith wet delay (ZWD). While the ZHD can be modelled analytically with high accuracy, the ZWD is more difficult to model and is therefore typically estimated empirically. Estimating ZWD with high accuracy is important because it is one of the major error sources for GNSS positioning. Furthermore, the ZWD is highly correlated to the water vapour content along the signal path and thus, interesting for GNSS meteorology. Therefore, many studies have investigated new methods to improve state-of-the-art ZWD models. Recently, also machine learning (ML) approaches have been used to create tropospheric delay models. In addition to modelling ZWD, forecasting of ZWD is of great importance. Due to the relation of ZWD to water vapour, accurate ZWD forecasts would be essential for weather forecasting.

The aim of this work is to develop a global ML-based model capable of forecasting ZWD for the next 24 hours at any point on Earth. It is trained on ZWDs, provided by the Nevada Geodetic Laboratory,  from over 10'000 GNSS stations and evaluated on ZWDs of 2700 test stations. The model utilizes the geographical location of the GNSS station and meteorological data from the ERA5 data set as its input features. To make hourly ZWD forecasts for the next 24 hours, forecasts of the meteorological data are taken from the Integrated Forecasting System of the European Centre for Medium-Range Weather Forecasts (ECMWF). Preliminary results using Extreme Gradient Boosting (XGBoost) show an average root mean squared error of around 1.5 cm over all testing stations for a forecasting horizon of 24 hours per day.

How to cite: Crocetti, L., Schartner, M., Schindler, K., and Soja, B.: Forecasting of tropospheric parameters using meteorological data and machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3453, https://doi.org/10.5194/egusphere-egu23-3453, 2023.

Precise modeling of the ionospheric Total Electron Content (TEC) is critical for reliable and accurate GNSS applications. TEC is the integral of the location-dependent electron density along the signal path and is a crucial parameter that is often used to describe ionospheric variability, as it is strongly affected by solar activity. TEC is highly depended on local time (temporal variability), latitude, longitude (spatial variability), solar and geomagnetic conditions. The propagation of the signals from GNSS (Global Navigation Satellite System) satellites throughout the ionosphere is strongly influenced by temporal changes and ionospheric regular or irregular variations. Here, we leverage transformer as an effective and scalable structure with self-attention mechanisms, for modeling long-range temporal dependencies for ionospheric TEC modelling based on GNSS data. 

The proposed transformer model is capable of learning long-range temporal dependencies. In seq2seq models, learning temporal dependencies is a demanding task, and often the model forgets the first part, once it completes processing the whole sequence input. Our model utilizes attention mechanisms and identifies complex dependencies between input sequence elements throughout the whole sequence.

Our model handles imbalanced datasets. Our work demonstrates that combining the unsupervised pre-training process with downstream task fine-tuning, offers a practical solution for ionospheric TEC modelling. This is a comparative advantage against the existing state-of-the-art works which, in most cases, fail to sufficiently model intense ionospheric variability conditions.

How to cite: Kaselimi, M., Doulamis, N., Doulamis, A., and Delikaraoglou, D.: A Transformer Model for Ionospheric TEC Prediction Using GNSS Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4303, https://doi.org/10.5194/egusphere-egu23-4303, 2023.

Hydrogeodesy is an applied scientific field that uses precise geodetic observations to measure or infer hydrological quantities and their changes over time. Recently, modern geodesy supplies hydrology with a very powerful tools based on the Earth’s artificial satellites, notably GRACE (Gravity Recovery and Climate Experiment) and GNSS (Global Navigation Satellite System). The long-term changes of periods higher than 1 year present in the time series of GNSS station displacements may be due to real geophysical effects, but may also be coupled to effects resulting from the superposition of GNSS systematic errors as well as numerical artefacts. As a result, it is often difficult to use the aforementioned changes to study, for example, long-term changes in the hydrosphere for specific GNSS station locations. Consequently, it is impossible to exploit the main advantage of GNSS over other measurement techniques, in the sense of dense spatial distribution in some parts of the world. In this study, we use wavelet analysis to determine long-term changes from GNSS station displacement time series and displacement time series determined from GRACE data and data from GRACE-assimilating high-resolution hydrological model GLWS v2.0 (Global Land Water Storage) provided by the University of Bonn. Global GNSS time series set was processed by the International GNSS Service (IGS) in the form of the latest reprocessing repro3.We correct the GNSS displacement time series for non-hydrospheric effects, such as non-tidal atmospheric effect, non-tidal oceanic effect, draconic period, post-glacial rebound and ground thermal expansion effects. We use a range of statistical analyses, such as correlation coefficient analysis and dynamic time warping (DTW) distance to assess the similarity of long-term changes between the three data sets. On this basis, we identify GNSS stations for which long-term changes can be analyzed in terms of changes in the terrestrial hydrosphere and those for which the long-term nature of the series is not due to changes in the hydrosphere, but to other effects.

How to cite: Mikocki, J., Klos, A., Gunes, O., Lenczuk, A., and Bogusz, J.: Demystifying long-term changes observed by GNSS: comparison with GRACE observations and hydrological models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5537, https://doi.org/10.5194/egusphere-egu23-5537, 2023.

Recent observations from Global Navigation Satellite Systems (GNSS) displacement time-series have demonstrated that the motion of tectonic plates is ubiquitously not steady-state. GNSS displacement time-series can be described as the sum of expected motions such as long term tectonic interseismic motion or annually and semi-annually seasonal oscillations, and unexpected “transients”, such as slow-slip events or volcanic deformations. Although the number and quality of globally available GNSS time-series have increased dramatically in recent years, detecting and modeling these signals remains challenging, because of their elusive nature, masked by the presence of noise. The most popular approach for filtering such noise is the application of common-mode-filters (CMFs) that use weighted averages of residuals after fitting individual time-series with trajectory models. CMFs exploit the spatial coherence of higher frequency noise in both Precise Point Positioning and network double difference solutions to systematically reduce the noise of each time-series. However, the application of CMFs is limited in the case of sparsely distributed GNSS stations. Additionally, CMFs can potentially map local transients into noise when the original trajectory model fits are made suboptimally.

Here we propose an alternative method to CMFs by exploiting Deep Learning (DL) techniques. Our supervised learning regression method aims to remove the noise present in each GNSS time-series regardless of its geographical location on a station-by-station basis. Our dataset consists of nine thousand time-series: all GNSS time-series available on the Nevada GNSS repository with at least 4 years of contiguous data. Our approach is defined by two subroutines. Firstly, the Greedy Automatic Signal Decomposition (GrAtSiD) algorithm is used to fit each time-series and leave behind a residual. GrAtSiD is a sequential greedy linear algorithm that decomposes the time-series into a minimum number of transient basis functions and some permanent functions. The residual time-series after signal decomposition is defined as noise, without qualifying its nature. Once this noise is identified, a DL model is trained to recognize this noise from the raw time-series, without the need for any trajectory modeling. The supervised learning regression model predicts what the residual to a trajectory model would be. Although GrAtSiD is very effective in isolating the high frequency noise of GNSS time-series, its fitting is dependent on the temporal length of input time-series. Additionally, GrAtSiD needs to set arbitrary thresholds which control the convergence of the inversion routine to avoid under- or over-fitting input data. In this context, our DL approach proposes a generalization of GrAtSiD solutions, by exploiting a weakly supervised training based on millions of examples - essentially, the model generalizes an optimal fit having seen many examples of GrAtSiD trajectory fits. This generalization allows the DL model to preserve apparent transient features of the time-series. A multitude of DL architectures are tested in both sequence-to-single and sequence-to-sequence regression framings. This exploration allows us to identify the best framing, architecture, and related hyperparameters for our method to be successful. With the best performing models, we demonstrate the effects of the DL high frequency noise removal and compare it to the CMF approach. 

How to cite: Mastella, G., Bedford, J., Corbi, F., and Funiciello, F.: A Deep-Neural-Network-Based Denoising Method For GNSS Displacement Time-Series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5560, https://doi.org/10.5194/egusphere-egu23-5560, 2023.

Water mass changes at and below the surface of the Earth cause changes in the Earth’s gravity field which can be observed by at least three geodetic observation techniques: ground-based point measurements using terrestrial gravimeters, space-borne gravimetric satellite missions (GRACE and GRACE-FO) and geometrical deformations of the Earth’s crust observed by GNSS. Combining these techniques promises the opportunity to compute the most accurate (regional) water mass change time series with the highest possible spatial and temporal resolution, which is the goal of a joint project with the interdisciplinary DFG Collaborative Research Centre (SFB 1464) "TerraQ – Relativistic and Quantum-based Geodesy".

A method well suited for data combination of time-variable quantities is the Kalman filter algorithm, which sequentially updates water storage changes by combining a prediction step with observations from the next time step. As opposed to the standard way of describing gravity field variations by global spherical harmonics, we introduced space-localizing radial basis functions as a more suitable parameterization of high-resolution regional water storage change. A closed-loop simulation environment has been set up to allow the testing of the setup and the tuning of the algorithm. Simulated GRACE and GNSS data together with realistic correlated observation errors will be used in the Kalman filter to sequentially update the parameters of a regional gravity field model. The implementation was designed to flexibly include further observation techniques (terrestrial gravimetry) at a later stage. This presentation will outline the Kalman filter framework and regional parameterization approach, and address challenges related to, e.g., ill-conditioned matrices and the proper choice of the radial basis function parameterization.

How to cite: Woehnke, V., Eicker, A., Weigelt, M., Güntner, A., and Reich, M.: Regional modeling of water storage variations in a Kalman filter framework, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5571, https://doi.org/10.5194/egusphere-egu23-5571, 2023.

Information on the distribution of free electrons in the Earth's ionosphere is needed for many applications, including the mitigation of single-frequency range delay errors and the monitoring of space weather. Most of the existing ionospheric models are generated using ground-based GNSS measurements, e.g., the Global Ionospheric Maps (GIM) provided by the International GNSS Service (IGS). However, the quality assessment of GIM is presently still an open question. In addition to altimetry Vertical Total Electron Content (VTEC) information over the oceanic regions, limited external data sources are available today to perform a fully independent validation of GNSS-based ionospheric models. The high-quality dual-frequency phase measurements of Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) system provide valuable opportunities to examine the Earth’s ionosphere. In this work, we analyzed the feasibility of using DORIS data to estimate the accuracy of GNSS-generated ionospheric models. To this end, the concept of DORIS differential Slant Total Electron Content (dSTEC) assessment is proposed. Using Jason-3 Near-Real-Time (NRT) DORIS data of the International DORIS Service (IDS), the accuracy of different Real-Time Global Ionospheric Maps (RT-GIM) as well as the IGS combined one is evaluated. The consistency between DORIS and GNSS dSTEC assessments in the quality analysis of RT-GIMs is also checked, and the overall Pearson correlation coefficient reaches 0.81 during the one-year test period. The DORIS dSTEC assessment can be used not only to estimate the accuracy of individual GIMs, but also to determine their weighting within a combination strategy. The performance of DORIS-dSTEC and GNSS-dSTEC combined GIMs is assessed by comparison to Jason-3 VTEC from the mission altimeter. The standard deviations are 4.71 TECu and 4.80 TECu for DORIS-dSTEC and GNSS-dSTEC combined GIMs, indicating the slightly better performance of DORIS-dSTEC combined RT-GIM in Jason-3 VTEC assessment. It was shown that NRT DORIS data can be used to independently validate and combine GNSS-derived ionospheric maps. In the future, it is also envisaged that DORIS data can be directly incorporated into ionosphere modeling. To this end, the provision of NRT data from other DORIS missions is planned (e.g., Sentinel-3).

How to cite: Wang, N., Dettmering, D., Li, Z., Liu, A., and Schmidt, M.: DORIS NRT data: an independent data source for GNSS-based ionospheric maps validation and combination, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7575, https://doi.org/10.5194/egusphere-egu23-7575, 2023.

The densification of high-quality, permanent GNSS stations in Europe enables a large-scale investigation of deformation processes on the Earth’s surface. This work aims to interpolate the horizontal and vertical GNSS station velocities and thus produce velocity fields showing the land motion for Switzerland, the Alps and Europe. The GNSS station velocities are provided by the EUREF Working Group on European Dense Velocities. The data set contains horizontal (east, north) and vertical velocities for around 8000 stations in Europe. Five interpolation methods are implemented and compared, namely, Inverse Distance Weighting (IDW), Ordinary Kriging, K - Nearest Neighbors (KNN), Random Forest and Multilayer Perceptron (MLP). Latitude and longitude of the station locations are used as input features for the interpolation. Additional input features will be engineered for Random Forest and MLP. Generally, the performance of all five interpolation methods with latitude and longitude as features evaluated on the test data by Root Mean Square Error (RMSE), Mean Absolute Error (MAE) and Mean Bias Error (MBE) is comparable for all velocity components in Switzerland, the Alps and Europe. RMSE and MAE vary among the methods by hundredths of a mm/year. The only exceptions are the horizontal velocity components for the extent of Europe, where MLP and Ordinary Kriging perform slightly worse than the other methods. The key findings of the qualitative analysis are that MLP and Ordinary Kriging produce the smoothest velocity fields, while IDW, KNN and Random Forest produce artifacts due to their mode of operation. All methods interpolate similar velocity fields where the station data is dense and greater differences when it is sparse. Especially for extrapolation areas where no data is available their performance is not verified. The interpolation of the GNSS station velocities in Switzerland, the Alps and Europe for this work shows that it is possible to produce velocity fields with accuracy level below 1 mm/year and the different phenomena of land motion can be clearly identified. 

How to cite: Hübner, L., Brockmann, E., Crocetti, L., Schindler, K., and Soja, B.: Land motion in Europe imaged by GNSS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8222, https://doi.org/10.5194/egusphere-egu23-8222, 2023.

Airborne laser scanning (ALS) point clouds are commonly acquired to describe a 3D shape of terrain and attributes of objects and landforms located on it. They proved to be useful in a variety of applications, including geometrical characterization of both man-made and natural objects and landforms. Usually, the first step of point cloud processing is classification. As a result, its accuracy highly influences the results of subsequent processing. Therefore, reliable and automatic point cloud classification is of key importance in most of the ALS data applications.

Recently, deep learning techniques attracted the attention of the community in the context of point cloud classification. However, the reproducibility of the trained deep learning networks remains unexplored because there is too little accessible and precisely classified 3D training data. Recently many countries have published their national ALS data sets. This initiative leads to promising options for deep learning classification of point clouds as it allows for comprehensive training of deep networks.

In this study we present the investigations that aimed at creation of a universal, deep learning based classifier that will be able to classify point clouds of varying characteristics. The experiments were carried out using selected parts of data sets that have been made available by three European countries: Poland, Austria and Switzerland. The point clouds were classified into four classes: ground and water, vegetation, buildings and bridges, and others. The results of the experiments showed that it is possible to achieve high overall accuracy of the classification for the ground and water (above 98%), vegetation (92-97%, depending on a test site), and building and bridges (92-96%, depending on a test site). A lower overall accuracy was achieved for class others because of a very high variability of geometry of objects that belong to this class. Furthermore, in some cases, adding training data from a different country to the initial training data resulted in improved classification accuracy in selected classes and reduced dataset-specific errors.

As a result, this study proves that it is possible to create a universal, deep learning based classifier that will be able to maintain high classification accuracy while it processes data sets of different characteristics.

How to cite: Walicka, A. and Pfeifer, N.: Deep learning based classification of multinational airborne laser scanning data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8538, https://doi.org/10.5194/egusphere-egu23-8538, 2023.

High-precision global ionospheric modeling is important for radio communication, navigation, or studies on space weather. Traditional spatial ionospheric modeling approaches include spherical harmonics and trigonometric B-splines. The Ionospheric Associated Analysis Centers (IAAC) of the International GNSS Service (IGS) use these methods to model vertical total electron content (VTEC) globally, and generate Global Ionospheric Maps (GIMs). Due to the limitations of spatial modeling approaches, conventional GIMs cannot comprehensively describe the spatial feature of the ionosphere. With the capability of capturing complex and non-linear relationships of diverse data, machine learning (ML) has been increasingly applied to ionospheric modeling. Currently, most of the existing ML-related studies focused on temporal prediction of ionospheric states and rarely considered the aspect of the spatial modeling of VTEC. Although some studies predicted global ionosphere maps using machine learning, they used conventional GIMs as inputs, implying that the precision of the ML-based spatial modeling could be limited by traditional methods and quantity of input GNSS observations utilized to generate GIMs.

The goal of this study is the spatial interpolation of VTEC using ML methods for the generation of ML-based GIMs. We first determine VTEC using carrier-to-code levelling through Kalman filter and based on geometry-free multi-GNSS observations from GNSS stations of the IGS network. The derived satellite-specific VTEC time series are then used to train the ML models. Several algorithms, such as extreme gradient boosting and random forest, are applied and their performance is evaluated. Moreover, VTEC from satellite altimetry is used as an additional means to assess the quality of the generated ML models. Finally, we compare the acquired ML-based GIMs with conventional GIMs to investigate the advantage of using the proposed approach for global VTEC modeling.

How to cite: Mao, S., Kłopotek, G., Awadaljeed, M., and Soja, B.: Machine learning for global modeling of the ionosphere based on multi-GNSS data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9260, https://doi.org/10.5194/egusphere-egu23-9260, 2023.

This study examines hydrological trend estimations derived from GRACE (Gravity Recovery and Climate Experiment) mascon solutions at the GSFC (Goddard Space Flight Center) in terms of the Equivalent Water Thicknesses (EWT) for the world's major river basins. The estimation of hydrological trends in mascon time series involves two steps: deterministic modeling and stochastic modeling. A deterministic model is characterized as a harmonic regression that incorporates trend and seasonal signals. For stochastic modeling, the EWT observables are typically considered to be equally weighted and uncorrelated, hence the term "white noise-only model". This interpretation, however, is misleading because typical discrete geodetic time series have temporal correlations, which generate colored noise. To explain the role of temporal correlations, we employ two different methodologies. Applying the least squares variance component estimation (LS-VCE) to time series for a combination of colored noise (i.e., flicker noise) and white noise is one of them. The second methodology uses autoregressive noise models to model the time series. Finally, the white noise-only model is compared to stochastic modeling incorporating temporal correlation. The findings show that a white noise-only model in a GRACE time series underestimates the uncertainty of the hydrological trend.

How to cite: Gunes, O. and Aydin, C.: Role of temporal correlations in the uncertainties of the GRACE hydrological trend, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9408, https://doi.org/10.5194/egusphere-egu23-9408, 2023.

Geothermal heat flow models are currently developed for remote areas like Antarctica and parts of Africa. Due to the sparsity of actual geothermal heat flow measurements, indirect data based on various quantities related, e.g., to gravitational and magnetic information are used for predicting heat flow in such regions and quantifying its uncertainty. Here we present and compare two common approaches, a data driven random forest approach that is trained with several covariates (magnetic and gravitational anomalies, lithospheric thickness, topography, seismic velocities) and a physics based approach relating magnetic anomalies to Curie depth and subsequently to geothermal heat flow (requiring various simplifications and a priori assumptions on the underlying physics). 

How to cite: Gerhards, C., Al-Aghbary, M., and Sobh, M.: Approaches to Modeling Geothermal Heat Flow from Various Datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9479, https://doi.org/10.5194/egusphere-egu23-9479, 2023.

In this study, when the height components of continuous GNSS stations were examined, it was seen that there were seasonal effects, and it was investigated whether the height components were related to meteorological parameters. Linear regression analysis was performed to obtain how dependent the height components of the continuous GNSS stations were on meteorological parameters. As a result of the analysis, the height components of the continuous GNSS stations are dependent on the meteorological parameters such as temperature, pressure, relative humidity, wind velocity and precipitation. In addition, height component time series analysis of continuous GNSS stations was performed by using Autoregressive Moving Average (ARMA) models from linear time series methods. As a result of the study, the performance of the ARMA modeling results again indicated the dependence of the height component of the continuous GNSS stations on the meteorological parameters.

Moreover, the measurements of Turkish National Permanent GNSS Network-Aktif (TUSAGA-Aktif) stations covering the 2014-2019 date range were used. The daily coordinates of GNSS stations were obtained as a result of GAMIT/GLOBK software solution. The analyzes subject to the study were carried out in Python.

Keywords: GNSS height component, Meteorological parameters, Linear Regression, ARMA Model

How to cite: Tekin Ünlütürk, N. and Doğan, U.: The Effects of Meteorological Parameters on GNSS Height Component, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9665, https://doi.org/10.5194/egusphere-egu23-9665, 2023.

The International GNSS Service (IGS) global ionospheric maps (GIMs) are one of the primary sources of information on the ionospheric state. They are used in many research and GNSS positioning applications. IGS GIMs are created using the weighted average of the products derived from the selected IAAC. This method allows for efficient mapping of the state of the ionosphere, especially on days without major disruptions. However, ionospheric disturbances could be more problematic to map correctly. To improve GIMs quality, we used a machine learning (ML) approach to combine individual IAAC GIMs into one product. We used total electron content (TEC) data from Jason altimetric satellite with a 5-minute interval as reference. To improve the modeling, we used auxiliary parameters such as solar and geomagnetic indices, e.g., F10.7 index. The training process was performed on the 2005-2020 dataset. 

This study presents some preliminary results of VTEC modeling using the ML approach. We show inter-validation and inter-comparison with IGS GIMs, and Jason-derived VTEC. We also used pseudorange code and carrier phase single-frequency GNSS observations to show positioning accuracy improvement achieved using ML-based GIMs. For this purpose, we used 34 evenly distributed IGS stations for the selected calm period and strong geomagnetic storms. The results showed that for both calm and stormy days, the differences between the coordinates obtained from our model and those using the IGS product were up to a few centimeters for most stations for the northern and eastern components of the topocentric coordinates. Additionally, for altitude, we noticed accuracy improvement for most stations during the storm periods relative to results obtained using the final IGS product.  

How to cite: Poniatowski, M., Nykiel, G., and Szmytkowski, J.: Application of machine learning to combine global ionospheric maps from IGS analysis centers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11443, https://doi.org/10.5194/egusphere-egu23-11443, 2023.

GIA from forward models suffer from large uncertainties due to approximations and assumptions on the Earth rheology and ice load history. These uncertainties propagate to uncertainties in ice-sheet mass balance and sea level budget studies. Therefore, GIA estimates from contemporary geodetic datasets are gaining interest. The challenges of obtaining data-driven GIA include solving a geophysical inversion that does not have a unique solution and often requires a-prior information and several approximations. In this work, a novel geophysical framework is developed that uses GPS and GRACE data to estimate GIA signal. The method relies on geophysical relations between geopotential and vertical land movement (VLM) caused by GIA and present-day mass changes. For example, the elastic response of solid Earth to the positive surface mass load results in a negative VLM, while a positive GIA mass leads to a positive VLM. We use these relations to express GPS observed VLM and GRACE observed gravity field anomalies in terms of GIA and present day mass change. The method is first shown to work in a closed-loop synthetic experiment and then applied to the NGL provided GPS velocities and GRACE spherical harmonic coefficients provided by ITG Graz. Our GIA estimates differ significantly from commonly used GIA models (such as ICE-6G) over Alaska and central Greenland. Our GIA rates over Alaska are around 5 mm/yr, which matches with several regional studies over Alaska. Similarly, there is a lot of ambiguity over Greenland ice-load history and our results may provide informative input to the ongoing debate. Our estimates are data-driven and are therefore able to pick them up. We also discuss the uncertainties, caveats and limitations of our method and its implications. The published GIA product is made openly available at one degree grid resolution. 

How to cite: Vishwakarma, B. D., Ziegler, Y., Royston, S., and Bamber, J. L.: A data-driven framework for estimating GIA from GPS and GRACE data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11697, https://doi.org/10.5194/egusphere-egu23-11697, 2023.

Dedicated satellite gravity missions, such as GOCE, GRACE and GRACE-FO, have been providing essential data for many geodetic and geophysical studies and applications. In the next future, new missions exploiting technological advances and innovative observation principles will be proposed, thus requiring numerical simulations to assess their performances in recovering information on the Earth gravity field. This is typically done by simulating the satellite orbits and propagating the instrumental noise to the error covariance matrix of the spherical harmonic coefficients. Of course, this propagation also depends on the processing techniques. Among them, approaches based on time-wise strategies are devised to directly map the time series of observations to spherical harmonic coefficients, while the approaches based on space-wise strategies are focused on the location of observations estimating the coefficients by some local analysis. In this work we compare a time-wise approach with a space-wise approach for the data analysis of possible future gradiometry missions, for example those based on quantum technology and based on the satellite tracking concept (pair or double pair of satellites, such as NGGM/MAGIC). The time-wise approach basically works in the Fourier transform domain, thus making the simulation very efficient from the computational point of view at the cost of some simplifications, e.g., in the data regularity and in the orbit repetition period. The time-wise approach permits a formal error propagation of realistic instrumental noise power spectral densities. On the other hand, the space-wise approach is focused on projecting the observed gravity information onto a spherical grid and then solving the boundary value problem to estimate the spherical harmonic coefficients. In estimating the grid values, the space-wise approach directly works in the space domain where a collocation method on local patches of data can be exploited for adapting the estimation to the local/regional characteristics of the gravity field. Differently from the time-wise approach, a formal error propagation from the instrumental noise power spectral densities is not feasible, e.g., for the limitations in modelling the error cross-correlation of grid nodes estimated from different data patches. Therefore, the overall error assessment relies on a Monte Carlo simulation. In this study, several numerical simulations are presented to emphasize the pros and cons of the two methods, as well as possible combination strategies to be exploited in studies of the time-variable models of the Earth gravity field.

How to cite: Vitti, A., Tesolin, F., Reguzzoni, M., Rossi, L., Koç, Ö., Batsukh, K., Albertella, A., and Migliaccio, F.: Comparisons and possible combinations of time-wise and space-wise approaches for satellite gravity missions data processing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12563, https://doi.org/10.5194/egusphere-egu23-12563, 2023.

The EUREF Permanent GNSS Network Central Bureau (EPN CB, www.epncb.eu ^[1]) monitors the quality of the daily GNSS observations of the EPN stations covering the period 1996-today. The associated data quality indicators (the number of observed versus expected observations in dual frequency, the lowest elevation cut-off observed, the number of missing epochs, the number of satellites, the number of maximum observations, and the number of cycle slips) are used to assess EPN stations' performance and as input for outlier detection in the daily position time series of the 400+ GNSS reference stations in Europe. Due to the increasing number of GNSS stations, the development of an automated algorithm to identify coordinate outliers caused by degraded GNSS data quality would allow to reduce the effort of human interpretation of the data quality indicators. We investigate the correlations between daily GNSS data quality metrics and daily position estimates to achieve this.

This study assesses several machine-learning classification algorithms to find a suitable data-driven model based on the correlation between degraded GNSS data quality metrics and quality degradation in position time series. Based on this investigation, the Random Forest algorithm proved to be the most precise algorithm, with an Area Under the Receiver Operating Characteristic Curve (AUC) equal to 0.95, and a correct classification of almost 90% of the test dataset. The GNSS data quality indicators ‘maximum observations‘ and ‘cycle slips’ are also shown as the most important parameters driving this model, which is in accordance with the data quality criteria for GNSS stations that IGS has determined ^[2]. Our model will be implemented in our EPN CB operation routine to develop a new monitoring system that can detect quality degradation on the GNSS station that will enable to improve the reliability of the EPN reference frame product by detecting position outliers due to degraded GNSS data quality. Here, we will present the current development of this automated algorithm, the challenges we faced, and the preliminary results of this work.

References:

^[1] C. Bruyninx, J. Legrand , D. Mesmaker, A. Moyaert, A. Fabian (2022): EUREF Permanent Network Central Bureau (EPN CB) Information System, https://doi.org/10.24414/ROB-EUREF-EPNCB

^[2] IGS (2019) Questions about the data quality graphs. https://kb.igs.org/hc/en-us/articles/204229743-Questions-about-the-data-quality-graphs

How to cite: Bamahry, F., Legrand, J., Bruyninx, C., Pottiaux, E., and Fabian, A.: Correlation Analysis of GNSS Data Quality Indicators and Position Time Series using Machine-Learning Algorithms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14585, https://doi.org/10.5194/egusphere-egu23-14585, 2023.

Atmospheric weighted mean temperature, T_m, is an important parameter in the Earth’s atmospheric water vapor sounding with the Global Navigation Satellite System (GNSS) technique. In this study, considering spatial distribution, time-varying characteristics, and the correlation with surface meteorological variables, T_m modeling is realized based on the random forest (RF) machine learning and global atmospheric profiles from radiosonde (RS) data and GPS radio occultations (RO) measurements. Comparisons of modeled results and numerical integrations of atmospheric profiles in 2020 show that the RF-based T_m model with surface meteorological parameters generally obtains a good accuracy with overall RMS errors of 2.8 K in comparison with RS data and 2.6 K in contrast to GPS RO data.

How to cite: Li, Q., Böhm, J., Yuan, L., and Weber, R.: Modeling of the weighted mean temperature based on the random forest machine learning approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17204, https://doi.org/10.5194/egusphere-egu23-17204, 2023.

In recent years, a significant challenge for geodesy has been the introduction of a global height reference system and the consideration of its regional or national applications. According to the Global Geodetic Observing System (GGOS) recommendations, providing and maintaining accurate and stable reference systems is highly desirable. Positioning of 3D spatial systems with regard to the reference ellipsoid is ensured by stable ITRF realisations and easily transformable local frames (e.g. ETRF). A more demanding task is the unification of vertical datums. The difficulties result from the multitude of height frames, their non-uniformity and usually missing elevation in-time change models. The uniform International Height Reference System aims to achieve an accuracy of 3 mm for heights and 0.3 mm/year for its velocities.

In this study, the authors focused on analysing the possible unification of the Polish national vertical datum (PL-EVRF2007-NH) with the IHRF. For this purpose, various global geopotential models (satellite and high-resolution GGMs) were tested. Their usefulness was checked in the context of the transition from the local system to the system related to the global geoid level recommended in IAG Resolution (No. 1). The impact of direct and indirect use of GGM to determine the normal heights of points in the IHRF frame in the national network was also examined. The first case included testing the possibility of obtaining normal heights based on height anomalies determined directly from the selected geopotential models. The second case involved the unification of systems on a national scale with a determined local ΔW₀ value ​​between the level of the PL-EVRF2007-NH and the W₀ of IHRS. To obtain reliable results, it was necessary to standardise input data with regard to the assumptions of the IHRS. In addition, a specific variant was tested in which the UELN (United European Leveling Network) points became the basis for a new realisation of the vertical datum in Poland.

The conducted analyses and numerical tests allowed for the formulation of recommendations regarding the methodology of unification of the PL-EVRF2007-NH and IHRF frames in Poland, in particular: evaluating and picking the optimal GGM model, selecting reference points for local height frame, collecting and assessing the quality of normal heights (or geopotential values) data.

How to cite: Marjańska, D., Walo, J., and Olszak, T.: Prospects for the unification of the PL-EVRF2007-NH frame with the International Height Reference System in Poland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-759, https://doi.org/10.5194/egusphere-egu23-759, 2023.

In several geodetic studies, the triaxiality of the Earth has been proven beyond a reasonable doubt, thus a triaxial ellipsoid is a better approximation and a more natural reference surface. As opposed to geodesics, plane curves on this surface are relatively easy to solve. These curves are produced by the intersection of a central ellipsoid and a plane and it is proved that they are in general ellipses. Therefore, we study the problems of the computation of an arc length of an ellipse and the determination of a point after a given length on an ellipse, using either a numerical or an approximate analytical method. Also, all the required transformations of the coordinates from the plane of the section to 3D space and conversely, are given. Subsequently, five types of planes of the ellipsoidal sections are determined: the central section, two normal sections, and two mean normal sections. Furthermore, the algorithms that solve the direct and inverse problems for these plane curves on a triaxial ellipsoid are described. Extended numerical experiments demonstrate the workability of the presented method which can also be applied to other celestial bodies. All developments in the literature assume the presence of an oblate spheroid and include an iterative scheme to solve the aforementioned problems. Alternatively, in this work, we provide the most general solutions to these problems applicable and for an oblate spheroid and all types of sections, without iterations.

How to cite: Filaretou, C. and Panou, G.: Plane curves on the Earth’s triaxial ellipsoid, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1219, https://doi.org/10.5194/egusphere-egu23-1219, 2023.

In the last decade, several numerical methods have been presented that transform Cartesian to geodetic coordinates on a triaxial ellipsoid. In this work, a new method for this transformation is presented. The method is based on ellipsoidal coordinates. To begin with, the Cartesian coordinates of a point are transformed to the respective ellipsoidal through closed analytical formulae. Following, the ellipsoidal coordinates referred to the referenced ellipsoid, approximated by those referred to the confocal ellipsoid passed through the given point. Then, the ellipsoidal coordinates are corrected by iterative and non-iterative formulae which are derived and thoroughly analyzed. After the successive approximations, the ellipsoidal coordinates are used for the computation of the foot point and hence of the geodetic coordinates by well-known formulae. The new method is validated by numerical experiments using an extensive set of points for different ellipsoids.

How to cite: Tsafaras, A. and Panou, G.: Transformation of Cartesian to geodetic coordinates on a triaxial ellipsoid using approximations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1459, https://doi.org/10.5194/egusphere-egu23-1459, 2023.

The coverage of the gravity data plays an important role in the geoid determination process. Still some parts in the world have poor gravity data coverage, with sometimes, large data gaps. Egypt (representing the situation in Africa) has sparse gravity data coverage over relatively large area. This paper tries to answer which type of gravity field signals at which resolution for filling the gaps would give the best geoid determination precision. This outcome is essential for the IAG sub-commission on the gravity and geoid in Africa in order to determine the African geoid with the best possible precision. Different types of gravity field signals have been used. They are gravity, geoid undulation and deflections of the vertical. Different resolutions of these signals are tested. The computed geoid precision for each case has been determined through the least-squares collocation technique (Moritz 1980). The results are shown and comprehensively discussed.

How to cite: Abd-Elmotaal, H. and Kühtreiber, N.: Experiment of filling the data gaps for better geoid determination: Case Study for Egypt (Africa), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1813, https://doi.org/10.5194/egusphere-egu23-1813, 2023.

In this contribution, we will discuss a problem of regional gravitational field modelling by the spectral combination of spaceborne first-, second- and third-order radial derivatives of the gravitational potential at the mean altitude of 250 km. Some of the mentioned measurements are not observable yet, so we will synthesize them from a global geopotential model over a test area. The main goal of a numerical experiment is to compute the gravitational field in a regional area from spatially restricted higher-order radial derivatives of disturbing potential, and two problems arise. The first is how to estimate local spectral properties, i.e., degree-order variances of local data, and the second is the effect of the omitted distant zone data, i.e., (spatial) truncation error. The spherical harmonic power spectrum from local data will be recovered by 2D-DFT, and the truncation error will be calculated from a global geopotential model. For this purpose, a mathematical model based on the spectral combination method of heterogeneous gravity field data and a global geopotential model is developed. The correctness of derived spectral weights suitable for spectral downward continuation will be verified by a closed-loop test and by direct comparison with the global solution. Moreover, different sizes of a data area (area covered by simulated satellite measurements) to minimize the truncation error and various truncation degrees of a global geopotential model will be tested.

How to cite: Pitoňák, M., Šprlák, M., and Novák, P.: Regional gravitational field modelling by the spectral combination of satellite higher-order radial derivatives of the gravitational potential and a global geopotential model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2718, https://doi.org/10.5194/egusphere-egu23-2718, 2023.

Since 2014, the National Geodetic Survey started to release experimental geoid models each year based on the new observations collected in the previous year, which are mainly from the contribution of the GRAV-D project (Gravity for the Redefinition of the Vertical Datum). While incorporating large amount of GRAV-D data into these yearly models, the implementation techniques are also polished from year to year, albeit the main architecture is still based on the Molodensky theory, essentially. This paper summarized these main technical improvements on computing local geoid models based on some hands-on experiences. It includes the update of reference models, the stabilization of airborne gravity downward continuation, the modification of residual terrain modeling, the inclusion of density variation effects, and the use of radial basis functions as well as the generalized Stokes’s integration to avoid the higher order terms. Although most of these steps are not totally independent from each other, numerical comparisons are given at each individual step to highlight their specific effects for interested researchers who may need to know the nitty-gritties. Then, the GSVS data are used to demonstrate the overall effects on the final model. Discussions for further improvements will be given at the end of the presentation.

How to cite: Li, X.: Technical Improvements on Local Geoid Model Computation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2895, https://doi.org/10.5194/egusphere-egu23-2895, 2023.

Thousands of permanent GNSS stations sample nowadays the 3D deformation of the Earth’s surface. The temporal covariance structure of the field of GNSS station displacements is well characterized and modelled. On the other hand, there lacks a general agreed-upon model of its spatial covariance structure, in part because the theory of random vector fields on the sphere remains hardly developed.

In this contribution, we show how the well-established theory of random isotropic scalar fields on the sphere generalizes to the case of vector fields. We derive in particular a spectral representation of random isotropic vector fields on the sphere in the domain of vector spherical harmonics, from which several properties of their covariance functions follow. We then present several parametric families of covariance functions which could be used to describe and model the covariance structure of vector fields on the sphere, such as GNSS station displacements.

Although this presentation focuses on theoretical aspects, it is given with future practical applications in mind. A realistic spatio-temporal covariance model of GNSS station displacements could indeed benefit different problems such as the estimation of long-term GNSS station velocities, the identification and mitigation of offsets in GNSS station position time series, the filtering of spatial “common modes” to isolate local deformation, or the spatial interpolation of GNSS station displacements into global maps. Applications may also be found in other domains involving vector quantities distributed on a sphere, e.g., winds, ocean currents, magnetic anomalies, etc.

How to cite: Rebischung, P. and Gobron, K.: Modeling random isotropic vector fields on the sphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3093, https://doi.org/10.5194/egusphere-egu23-3093, 2023.

In the literature, there are discrepancies about the direction in which the telluroid points should be plotted from the ellipsoid for the subsequent calculation of the segment of normal height.

There are three options: forceline of the normal field back, coordinate line of the spheroidal system, normal to the ellipsoid.

Theoretically, the normal gravity field can be successfully used as an orthogonal coordinate system, since its force lines and level surfaces can serve as natural coordinate lines and coordinate surfaces. However, a normal force line does not have two characteristics that would be constant at each of its points with a change in only the third value, as in a conventional orthogonal coordinate system. The normal to the reference ellipsoid plays an important role in solving geometric problems of geodesy, but is of little use in physical matters. It is more convenient to use a curvilinear coordinate system associated with a family of ellipsoids confocal to the reference one, especially since it contains closed expressions for the normal potential of gravity and all derivative elements. The method used so far for calculating the value of the normal height is based on the expansion of the normal gravity in a series using higher derivatives with respect to the geodetic coordinates at the point on the surface of the reference ellipsoid, the expansion error naturally increases with distance from the ellipsoid. This Yeremeyev's formula is often considered as the definition of the normal height while it is only working formula

For the first time, the question of the need to study and refine the method for calculating the normal height was raised by M. Pick and M. I. Yurkina in 2004. In their joint publication, the normal height is refined with respect to the gradient solution, taking into account the expression of the normal potential in the spheroidal system u, v, w (Niven), but there is no calculation of the length of the normal force line segment.

M. I. Yurkina in 2004 gave a similar expression in the system Heiskanen-Moritz, also indicating an explicit expression for the length of the segment of the coordinate line in the same system, however, the control calculations were not performed, so inaccuracies remained unnoticed in the proposed formulas for the auxiliary quantities, resulting in a low accuracy of the expression for the normal height H^γ.

A detailed way contains three steps:

1. Standard calculation by the above Yeremeyev's formula and the corresponding third spheroidal coordinate w′ or b′. This is the first approximation.

2. Refinement of the third spheroidal coordinates of the points on the telluroid from the Molodensky's condition:

the reduced latitude u could be precised consequently.

3. Evaluation of the curvilinear integral from w = w₀ to w:

where

[Here was the inaccuracy in the Yurkina M. I. (2004) To refine the height to fractions of a millimeter, this step is absent in the paper Jurkina M. I., Pick M. (2004) Návrh na zpřesnění výpočtu normálních výšek].

How to cite: Popadyev, V. and Rakhmonov, S.: High-precision calculating the normal height as the coordinate line's length, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3334, https://doi.org/10.5194/egusphere-egu23-3334, 2023.

Within this contribution we present a method that allows a smooth integration of in-situ ground gravity observations into high-resolution global models up to d/o 5400 (2’ global resolution). The functionality is shown on the example of the airborne GRAV-D gravity dataset which is integrated into a global satellite-topographic spherical harmonic model. Conceptually, the method is divided into three steps: firstly, since the processing is based on residuals, a precursor model needs to be identified which is used for reducing the observations. In the actual example a combination between a satellite-only model (GOCO06s) and topographic model (EARTH2014) is chosen (named SATOP2) to ensure independency to the observations. Secondly, the previously reduced (GRAV-D) observations are gridded onto a regular geographic grid making use of the recently developed partition-enhanced least squares collocation approach (PE-LSC). PE-LSC allows an efficient collocation of virtually arbitrary large datasets using a partitioning technique that is optimized for computational performance and for minimizing fringe effects. As a third and last step, the obtained regular grid gets analyzed and combined with a satellite-only model (GOCO06s) on the normal equation level up to d/o 5400. This can be achieved efficiently by using a so-called kite-normal equation system which emerges when combining dense and block-diagonal normal equation systems (assuming equal accuracies for the ground gravity grid). The herby obtained global gravity field model, named SGDT, is dominated by the satellite information in the lower frequencies (up to d/o 200), by GRAV-D in the mid-frequencies (d/o 200-2000) and by the topographic information in the high frequencies (above d/o 2000). The main purpose of the SGDT model is to validate the method itself and to allow a comparison of GRAV-D observations to pre-existing ground-gravity data by synthesizing SGDT to actual observation sites.

How to cite: Roman, D., Li, X., Zingerle, P., Willberg, M., and Pail, R.: Integrating NGS GRAV-D gravity observations into high-resolution global models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3363, https://doi.org/10.5194/egusphere-egu23-3363, 2023.

The GRACE and GRACE-FO satellite missions have established mass variations as a fundamentally new observation type for a broad spectrum of applications in Earth science disciplines, including oceanography, geophysics, hydrology and hydrometeorology. Despite its innovation and success in hydrology, the utility of GRACE-derived Terrestrial Water Storage Anomaly (TWSA) and its time derivative Terrestrial Water Storage Flux (TWSF) have mainly been limited to large catchments due to their coarse spatial resolution. 

Here, we propose a method to downscale TWSF and determine its uncertainty within a Bayesian framework by incorporating fine-scale (non-GRACE) data of TWSF and of Soil Moisture Change (SMC) from different available sources. For the Bayesian ingredients, we take GRACE data as the prior and make use of copula models to obtain non-parametric likelihood functions based on the statistical relationship between GRACE TWSF with fine-scale TWSF data and SMC. We apply our method to the Amazon Basin and assess the performances of our products from various fine-scale input datasets of TWSF and SMC. 

Given the lack of ground truth for TWSF, we validate our results against 2 external information sources: (1) space-based observations of Surface Water Storage Change (SWSC) in the Amazon river system and (2) Vertical Crustal Displacements (VCD) observed by the Global Positioning System (GPS). Overall, the results show that the proposed method is able to estimate a downscaled TWSF, which is informed by GRACE and fine-scale data. Validation shows that our downscaled products are better anticorrelated with VCD (-0.81) than fine-scale TWSF (-0.73) and show a mean relative RMSE of 26% with SWSC versus 70% for fine-scale TWSF. 

The proposed methodology, although developed in a context of hydrology and of GRACE data, is generic to a high degree. Within hydrology it can be used for other datasets, which are crucial for hydrological application at regional and local scales. Moreover, the methodology can easily be extended to other disciplines in which downscaling of coarse scale datasets is relevant.

How to cite: Sneeuw, N., Tourian, M., Saemian, P., Ferreira, V., Frappart, F., and Papa, F.: A copula-supported Bayesian framework for spatial downscaling of GRACE-derived terrestrial water storage flux, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3384, https://doi.org/10.5194/egusphere-egu23-3384, 2023.

Spherical harmonics are widely used to represent the gravitational field of the Earth and other celestial bodies. These harmonics include Legendre’s polynomials. However, the numerical computation of these polynomials is a difficult issue, especially to a high degree. In the literature, several algebraic or numerical methods have been proposed to compute Legendre polynomials with acceptable precision within reasonable time, avoiding instabilities due to underflow or overflow problems. These methods have their advantages and disadvantages. For example, cannot be used for parallel computations. In this contribution, we are developing a new scheme for the numerical computation of Legendre polynomials. The problem of underflow/overflow is managed by using trigonometric identities and a technique based on successive ratios. The performance of the proposed scheme is demonstrated by several numerical experiments. In addition, the results are compared with other methods in terms of stability, precision, and speed. Finally, we suggest means for the generalization of the proposed algorithm in the numerical computation of the related Legendre functions for high degrees and orders.

How to cite: Panou, G., Koci, J., and Iossifidis, C.: New scheme for numerical computation of high degree Legendre polynomials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3815, https://doi.org/10.5194/egusphere-egu23-3815, 2023.

In recent years, high-order gravitational potential gradients and variable density models are the potential research topics in gravity field modeling. This paper focuses on the variable density model for gravitational curvatures (or gravity curvatures, third-order derivatives of gravitational potential) of a tesseroid and spherical shell in the spatial domain of gravity field modeling. In this contribution, the general formula of the gravitational curvatures of a tesseroid with arbitrary order polynomial density is derived. The general expressions for gravitational effects up to the gravitational curvatures of a spherical shell with arbitrary order polynomial density are derived when the computation point is located above, inside, and below the spherical shell. The influence of the computation point's height and latitude on gravitational curvatures with the polynomial density up to fourth order is numerically investigated using tesseroids to discretize a spherical shell. Numerical results reveal that the near-zone problem exists for the fourth-order polynomial density of the gravitational curvatures, i.e., relative errors in log10 scale of gravitational curvatures are large than 0 below the height of about 50 km by a grid size of 15'x15'. The polar-singularity problem does not occur for the gravitational curvatures with polynomial density up to fourth order because of the Cartesian integral kernels of the tesseroid. The density variation can be revealed in the absolute errors as the superposition effects of Laplace parameters of gravitational curvatures other than the relative errors. The derived expressions are examples of the high-order gravitational potential gradients of the mass body with variable density in the spatial domain, which will provide the theoretical basis for future applications of gravity field modeling in geodesy and geophysics. This study is supported by the Alexander von Humboldt Foundation in Germany.

How to cite: Deng, X.-L.: Gravitational curvatures for a tesseroid and spherical shell with arbitrary order polynomial density, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3881, https://doi.org/10.5194/egusphere-egu23-3881, 2023.

Spherical harmonic expansions are routinely used to represent the gravitational potential and its higher-order spatial derivatives in global geodetic, geophysical, and planetary science applications. The convergence domain of external spherical harmonic expansions is the space outside the minimum Brillouin sphere (the smallest sphere containing all masses of the planetary body). Nevertheless, these expansions are commonly employed inside this bounding surface without any corrections. Justification of this procedure has been debated for several decades, but conclusions among scholars are indefinite and even contradictory.

In this contribution, we examine the use of external spherical harmonic expansions for the gravitational field modelling inside the minimum Brillouin sphere. We employ the most recent lunar topographic LOLA (Lunar Orbiter Laser Altimeter) products and the measurements of the lunar gravitational field by the GRAIL (Gravity Recovery and Interior Laboratory) satellite mission. We analyse selected quantities calculated from the most recent GRAIL-derived gravitational field models and forward-modelled (topography-inferred) quantities synthesised by internal/external spherical harmonic expansions. The comparison is performed in the spectral domain (in terms of degree variances depending on the spherical harmonic degree) and in the spatial domain (in terms of spatial maps). To our knowledge, GRAIL is the first gravitational sensor ever, which helped to resolve the long-lasting convergence/divergence problem for the analytical downward continuation of the external spherical harmonic expansions, see (Šprlák and Han, 2021).

References

Šprlák M, Han S-C (2021) On the Use of Spherical Harmonic Series Inside the Minimum Brillouin Sphere: Theoretical Review and Evaluation by GRAIL and LOLA Satellite Data. Earth-Science Reviews, 222, 103739, https://doi.org/10.1016/j.earscirev.2021.103739.

How to cite: Šprlák, M., Han, S.-C., Pitoňák, M., and Novák, P.: Evaluation of external spherical harmonic series inside the minimum Brillouin sphere: examples for the lunar gravitational field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3913, https://doi.org/10.5194/egusphere-egu23-3913, 2023.

Abstract: Global Navigation Satellite System-Reflectometry (GNSS-R) technique has been used to obtain sea surface height (SSH) since the 1990s. Due to the short wavelengths and low power of GNSS signals, the continuously tracked carrier phase measurements of reflected signals are usually unavailable for sea surfaces with big roughness, varying over space and time. Under high sea states, the phase difference cannot be well retrieved from carrier phase measurements, especially for the signals with high elevation angles. To overcome these shortcomings related to temporal incoherence, we propose an improved algorithm to extract the combined interferometric phase difference measurements between direct and reflected signals. We improve the configuration of GNSS-R altimetry software-defined receiver (SDR) by reconstructing ‘clean’ direct signals to compute phase differences between direct and reflected signals. The interferometric phase differences are combined in the complex domain and the resulting interferometric signal is refined through open-loop tracking with 60-s coherent integration before the phase difference measurements are extracted, without tracking their respective carrier phase measurements in advance.  In order to verify our method, a coastal experiment under different sea conditions was conducted. Raw intermediate frequency data of Quasi-Zenith Satellite System were collected and processed by SDR to compute the path delay measurements of L1 and L5. Under high sea states, the phase delay measurements of L1 and L5 were random over time, while phase delay can still be well recovered based on the proposed method even in the case of high elevation angles. The altimetry solutions were compared with the in situ observations from a radar altimeter instrument. The results show that centimeter-level altimetry accuracy can be achieved under high sea states using the proposed method The same SDR and method are applied in the shipborne altimetry experiment, the interferometric phase observations are successfully extracted on both ship motion and statics. Also, the integer ambiguity in the interferometric phase observations is well estimated. The differences in the SSH measurements between different satellites is at centimeter level. The coastal and shipborne experiments demonstrate that the dual-antenna GNSS-R phase altimetry technique can be used for low-cost tide gauges on different platforms to monitor sea levels.

Acknowledgments: This work was supported by Natural Science Foundation of China (42192534) and Key Research and Development Program of Shandong Province (Major Technological Innovation Project, 2021ZDSYS01).

How to cite: Xu, T., He, Y., Gao, F., and Meng, X.: High-precision GNSS-R Altimetry based on Carrier Phase Measurement Combination, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4062, https://doi.org/10.5194/egusphere-egu23-4062, 2023.

The North American Vertical Datum of 1988 (NAVD88) was established by the minimum-constrain adjustment of geodetic levelling observations in Canada, USA, and Mexico. It held fixed the height of the primary tidal benchmark at Rimouski, Quebec, Canada. The NAVD88 datum was never officially adapted in Canada due its large east-west tilt of 1.5 m from the Atlantic to Pacific coast (Hayden et al., 2012). Also, a large systematic difference (ranging from -20 cm to +130 cm) was found between NAVD88 and the pure geoid gravimetric models. Using Factor Analysis it was discovered that one of the factors, which can explain the tilt of the NAVD88, is the terrain, i.e. small in the flat states but large in the mountainous areas such as in the Rockies and the Appalachians (Li, 2012). A possible reason for the tilt of the NAVD88 might be the weights used into adjustment of the network. In this study the data of two precise national levelling networks are used, e.g. the Second Levelling of Finland and the Third Levelling of Bulgaria, in order to support the above hypothesis. An iterative procedure based on the Inverse Absolute Height Weighting (IAHW) is applied. The core of this procedure is to find this value of the power parameter (p) of the weights w=H^p, where H is the absolute elevation difference of the terminals in the levelling lines, that minimize the mean of the mean squared errors (MSE) of the nodal bench marks (NBM) in both networks. It has been found that p=1 and p=4.3 for the Bulgarian and the Finnish networks, respectively. Also, a similar iterative procedure based on the Inverse Distance Weighting (IDW) is performed and the best decisions for the Finnish and the Bulgarian networks are obtained. It has been found that the weights w=L^-5.9 and w=L^-1.6, where L is the length of the levelling line, lead to the minimal MSE of the NBM for the Finnish and the Bulgarian networks, respectively. The results of both the IDW and the IAHW procedures are compared. It has been revealed that the IAHW based adjustments lead to significantly less MSE of the NBM than all variants of the IDW. It has also been shown that concerning the Bulgarian and the Finnish analyzed here data, the IAHD approach leads to physically lower adjusted heights than the IDW. In some cases these differences are more than 1.5-2 times greater than the MSE of the corresponding bench marks.

How to cite: Cvetkov, V. and Gospodinov, S.: Inverse Absolute Height Weighting in the Highest Order Levelling Networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4219, https://doi.org/10.5194/egusphere-egu23-4219, 2023.

In local and regional quasi-geoid modeling, the residual terrain modeling (RTM) method is often used to remove the short-wavelength gravity field signals from the measured gravity both on the ground and up in the air, in order to obtain the regularized and smooth gravity field which is suited for field interpolation and modeling. Accurate computation of RTM corrections requires a set of fine-tuned parameters in terms of the gravity forward modeling technique, digital elevation model (DEM), reference topography, and integration radius for the inner zone and outer zone. To our limited knowledge, this has not been systematically documented, albeit its importance is obvious. This work aims to clearly investigate the impact of these factors on the RTM correction computation and their effects on the quasi-geoid modeling so to provide practical guidelines for real applications. Two gravity forward modeling techniques, i.e., the prismatic approach and the tesseroidal approach, are employed to investigate the following issues existing in the practical use of the RTM method: ① can a combination of a high-resolution DEM and a DEM with a lower resolution replace the use of a single high-resolution DEM for the RTM correction computation without loss of accuracy? ② how to properly choose the integration radius for the inner zone and outer zone while costing less time and keeping the accuracy? ③ what are the performances of using the reference topographies obtained by the direct averaging, the moving averaging, and the spherical harmonic analysis and synthesis on the RTM correction computation and quasi-geoid determination? For obtaining objective findings, two research regions are selected for this investigation. One is the Colorado area (USA) having quite rugged terrains and the other is the Auvergne area (France) with moderate terrains. The numerical results show that, in the computation of RTM corrections to gravity anomaly and height anomaly, the combination of a dense DEM and a coarse DEM can replace the use of a single dense DEM without loss of accuracy. The increasing and decreasing of the integration radius for the inner zone and outer zone do not influence the RTM correction computation much. The recommended values are 10 km for the inner zone and 111 km for the outer zone. The use of different reference topographies changes RTM corrections, however, the final quasi-geoid models are at the similar accuracy level.

How to cite: Lin, M., Li, X., and Yang, M.: Numerical experiences on using the RTM method in quasi-geoid modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4935, https://doi.org/10.5194/egusphere-egu23-4935, 2023.

In geodesy, the Earth's external gravitational field is often modelled by a single finite set of external spherical harmonic coefficients. The coefficients are usually derived from satellite or terrestrial gravitational data or by a suitable combination of both. It is known, however, from previous theoretical studies that satellite and terrestrial coefficients are conceptually different and, in principle, do not match. On the one hand, both types can describe the external potential with an arbitrary accuracy in the space above the limit sphere encompassing the gravitating body. On the other hand, when it comes to realistic bodies, only terrestrial coefficients can achieve the same in the space that is below the limit sphere but external to the gravitating body. The price paid to achieve the latter is the fact that the terrestrial coefficients no longer match the satellite coefficients, introducing a conceptual coefficients inconsistency. Using a carefully designed simulated yet realistic closed-loop environment, we numerically reveal in this contribution the different nature of the two coefficients sets. Taking the irregularly-shaped asteroid (101955) Bennu as the gravitating body, we show that, unsurprisingly, the satellite coefficients indeed lead to an excellent accuracy outside the limit sphere (relative accuracy of 10^-14 in double precision) but produce grossly invalid results below the limit sphere due to the divergence of spherical harmonics. After this exercise, the real challenge of the study was to reliably compute terrestrial coefficients for as complex body as the asteroid Bennu. After computations that took altogether 90 CPU years, we were able to scrutinize the terrestrial coefficients with the relative accuracy of 10^-6 on the surface of Bennu, that is, below the limit sphere. The results clearly demonstrate the different nature of the two coefficients sets. For instance, it is evident that, from the theoretical point of view, it is rather dangerous to evaluate partial sums from terrestrial coefficients on the Earth's surface. Furthermore, some of the near-surface applications of terrestrial coefficients (e.g., quasigeoid-to-geoid separation or residual terrain modelling) become questionable. As a consolation, the accuracy and the resolution of our Earth's gravitational field models are currently so poor (or excellent, depending on the context) that it will probably take some time for us to encounter these effects with real-world Earth's gravitational data.

How to cite: Bucha, B. and Sanso, F.: Satellite and terrestrial spherical harmonic coefficients of the external gravitational potential do not match, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6147, https://doi.org/10.5194/egusphere-egu23-6147, 2023.

The “non-harmonicity” problem, as one of the main problems in the residual terrain modelling (RTM) method, would involve more than 200 mGal errors in the gravity field determination over the Himalaya area. To deal with it, there are five main harmonic correction (HC) methods, i.e., the condensation method, regularized downward continuation method with Taylor series expansions (TS), regularized downward continuation method with spherical harmonics (SH), complete HC method, and Kadlec's method, being provided in previous studies. However, their performances in gravity field determination are not studied nor compared directly yet. In this study, all these five HC methods are completely reviewed and evaluated, especially their performances in regional geoid determination. The expressions of HCs under various approximations are derived, and the Kadlec’s method is proved to be equivalent to the condensation method when adopting the same approximation for Bouguer masses. For the continuation methods, the HC associated with the complete method shows large differences compared to the HC associated with TS and SH methods. This is caused by the fact that the continuation process within the complete method is implemented in the situation of the Earth’s masses being changed. To cope with this problem, we promote a new three-step approach for computing the HC which is proved to be equivalent to the HC using the TS method. Then the HCs with various methods are completely considered and evaluated in the Colorado geoid determination using the remove-compute-restore technique. The best performance is achieved when the SH method is adopted for computing the RTM corrections to gravity anomaly in the removal procedure. The accuracy of the calculated geoid height is ~1.62 cm. Involving HCs for geoid height in the restore procedure would slightly improve the results to an accuracy of ~1.56 cm.

How to cite: Yang, M., Li, X., Lin, M., Feng, W., and Zhong, M.: Harmonic Correction in Regional Gravity Field Determination, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6403, https://doi.org/10.5194/egusphere-egu23-6403, 2023.

The official national height reference systems in use, apply different definitions of the height and the zero levels refer to different tide gauges and epochs. Additionally, the treatment of the permanent tide is not entirely consistent. This causes differences at the decimetre scale, which also vary along the national borders. The "European Alps Geoid Project" (EAlpG) aims to harmonize the basis for height determination in the Alpine region, including the neighbouring lowlands and the computation of a uniform geoid model according to European standards for height and positioning.

The project is based on the experiences and findings of the predecessor "D-A-CH geoid" project, which covered a test area around Lake Constance. It was a joint initiative of the federal and state authorities responsible for land surveying in Germany, Austria and Switzerland.

First steps of the EAlpG project were the conclusion of the Memorandum of Understanding in May 2022 as well as the initiation of the exchange of gravity and height data. The ambitions of the initiative are therefore to intensify the cooperation’s between the partners in regional gravity field modelling and to provide better information on the transformations between the national height systems. The following activities are planned:

1. Improved cross-border regional geoid model of the Alpine area:

• Revision and harmonization of the base data for the calculation of the geoid models: gravity data, digital elevation models, control points for validation
• Cross-border gravity measurements, e.g. Austria, France, Germany, Italy, Switzerland
• Comparative studies on geoid modeling in high mountains

2. Improved height transformation between the Alpine countries:

• Extensive comparative investigations and validation between the national height reference surfaces (geoid models and other height transformation grids) and the national and European heights along the borders
• Derivation of consistent height transformation models accurate to a few centimeters
• Development of a corresponding web application

The outcomes of the project will support (non-)geodetic users in there cross-border height applications, e.g. ground water level investigations, flood protection. Other important applications for cross-border height standardisation are engineering projects such as tunnels, bridges, supply lines, etc.

The results will be embedded in a pan-European geoid initiative within EUREF. Contributing to the upcoming EUREF Working Group “European Height Reference Surface”, the European Alps Geoid will be one of many cornerstones to build an official EVRS height reference surface.

The EAlpG project is a joint initiative of the national authorities and organization responsible for or involved in the integrated geodetic spatial reference of Austria, Czech Republic, France, Germany, Hungary, Italy, Slovakia, Slovenia and Switzerland. The scientific work is supported by various universities in the Alp area.

How to cite: Bauer, T. and Schwabe, J. and the The European Alps Geoid group: The European Alps Geoid (EAlpG) Project – a joint initiative for improved cross-border regional geoid modelling and height transformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7431, https://doi.org/10.5194/egusphere-egu23-7431, 2023.

The physics-informed neural networks (PINN) are emerging as a new tool for gravity field modeling. In some scenarios, such as near-source gravitational fields representation, PINN may have greater potential than traditional spherical/ellipsoidal harmonics solutions, as the latter suffers from both theoretical and numerical divergence problems for sources with complex geometry. By incorporating observational, geometrical and statistical density information into the neural network, we aim to reduce the non-uniqueness of the solution space, therefore obtaining improved accuracy in representing gravity fields, especially near the source body. By transforming the trained gravitational potential into density distribution through Poisson's equation, we also provide a new perspective to observe the evolution of the neural network for gravity field modeling as "redistribution of equivalent density sources". The influence of multiple parameters of the neural network on the performance of the PINN gravity modeling, including its size and shape, distribution of Laplacian and Poisson collocation points, and balance between loss functions of the multiple constraints applied, are also investigated. Numerical results are illustrated using the EROS asteroid model and a regional DEM model of Colorado Geoid Experiment area.

How to cite: Wu, L., Chen, L., Livermore, P., de Ridder, S., and Zhang, C.: Physics-Informed neural networks for gravity field modeling incorporating observation, geometry and density constraints, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8952, https://doi.org/10.5194/egusphere-egu23-8952, 2023.

This research introduces the formation of a Geoid model that is based on terrestrial gravity measurements in Israel and its surroundings, together with shipborne gravity measurements and altimetry data over the Mediterranean Sea, using the EIGEN-6C4 as the reference earth gravity model – the first of a kind effort done in Israel to construct such a model. A challenging aspect for establishing this model for this area - that does not exist elsewhere in the world - is that approximately 20% of Israel's land area is located below sea level, some of which is minus 430 meters, mainly along the Dead Sea Rift. This unique topography requires new and challenging computation theories for gravimetric Geoid determination.

The results yield a standard deviation value of the gravimetric Geoid of 5.7 cm. The model is also successfully calculated in areas with a negative orthometric altitude, which proves for the first time the potential of the developed methodology of obtaining an accurate geoid model. The hybrid Geoid model significantly improves these values, where the standard deviation value is reduced to 2 cm with an error range of 22 cm. The hybrid Geoid model retains the orthometric datum of the control points while relying on gravimetric data to provide better gradient information about the area. The high accuracy of the hybrid Geoid model will allow the integration of the official national Geoid model and the new gravimetric Geoid model to support precise GNSS measurements used for precise infrastructure engineering projects. The gravimetric geoid can recreate a role with other local gravity models developed by countries surrounding Israel.

How to cite: Sarid, H., Dalyot, S., and Wang, Y.-M.: The first Gravity Geoid Model for Israel, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9678, https://doi.org/10.5194/egusphere-egu23-9678, 2023.

The U.S. National Geodetic Survey (NGS), an office of the National Oceanic and Atmospheric Administration (NOAA), is preparing for the release of a new vertical datum, the North American-Pacific Geopotential Datum of 2022 (NAPGD2022). This new datum will be based on a high degree spherical harmonic model of the Earth’s gravitational potential, and will yield a geoid undulation model (GEOID2022) to calculate orthometric heights from GNSS-derived ellipsoid heights.

A critical component of this new vertical datum is the terrain model that will be used for the geoid computation. Currently, an experimental version of this terrain model has been developed at NGS, the experimental Digital Elevation Model 2022 (xDEM2022). The xDEM2022 is composed of data from TanDEM-X, MERIT, and USGS 3DEP elevation data sets. Bathymetry and Ice thickness data has also been added to the latest version of the xDEM2022. An overview of the xDEM2022 will be presented with comparisons to other independent elevation datasets. Uses of this terrain model for geoid modelling at NGS will also be shown.

How to cite: Krcmaric, J. and Li, X.: The experimental xDEM2022 and its uses for geoid modelling at NGS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10030, https://doi.org/10.5194/egusphere-egu23-10030, 2023.

The boundary element method (BEM) as a numerical method can be applied for high-resolution gravity field modelling. To obtain numerical solutions of “cm-level” accuracy, it requires very refined level of the disretization which leads to enormous memory requirements. An implementation of the Hierarchical Matrices (H-matrices) can significantly reduce a numerical complexity of the BEM approach. Here we present an implementation of the Adaptive Cross Approximation (ACA) algorithm into the direct BEM formulation applied for the global gravity field modelling. The ACA algorithm is based on a multilevel matrix-partitioning scheme of the rank-revealing LU decomposition, which uses a low rank of the submatrix belonging to two far groups of points. The algorithm performs a series of decompositions, which results in an approximation of the original submatrix using the product of two sparse matrices with low ranks. This approach can significantly reduce enormous memory requirements. Numerical experiments present efficiency of the ACA algorithm that can achieve a memory saving of 98% for the very refined meshes.

How to cite: Čunderlík, R. and Bejdák, M.: The ACA algorithm implemented into the direct BEM approach to reduce its numerical complexity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12798, https://doi.org/10.5194/egusphere-egu23-12798, 2023.

We present an iterative approach for solving the nonlinear satellite-fixed geodetic boundary value problem (NSFGBVP) by the finite element method that is applied for a determination of local quasigeoid in Himalayas and Andes. At first, we formulate the NSFGBVP that consists of the Laplace equation holding in the 3D bounded domain outside the Earth, the nonlinear boundary condition (BC) prescribed on the disretized Earth's surface, and the Dirichlet BC given on a spherical boundary placed approximately at the altitude of chosen satellite mission and additional four side boundaries. Then the iterative approach is based on determining the direction of actual gravity vector together with the value of the disturbing potential. Such a concept leads to the first iteration where the oblique derivative boundary value problem is solved, and the last iteration represents the approximation of the actual disturbing potential and the direction of gravity vector. As a numerical method for our approach, we have implemented the finite element method with triangular prisms. Finally, we present a high-resolution numerical experiment dealing with the local gravity field modelling in Himalayas and Andes.

How to cite: Macák, M., Minarechová, Z., Čunderlík, R., and Mikula, K.: A local quasigeoid determination by solving the nonlinear satellite-fixed geodetic boundary value problem, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13000, https://doi.org/10.5194/egusphere-egu23-13000, 2023.

Within the GeoNetGNSS project, funded by the European Union and National Funds through the Region of Central Macedonia (RCM), the main goal is to establish a dense network of Continuously Operating Reference Stations (CORS) in Northern Greece. Accuracy, reliability, wide coverage, ease of use and cost effectiveness are among the main advantages of differential positioning supporting mapping, surveying, geodetic, and large infrastructure projects. However, as ellipsoidal heights from GNSS measurements have no physical meaning, they should be transformed to orthometric heights. This transformation requires an accurate gravimetric geoid model to be readily available, in order to carry-out the so-called GNSS/Leveling, i.e., the determination of orthometric heights without the need to carry out levelling. With that in mind, a regional gravimetric geoid was determined based on historical and newly acquired high-accuracy and density gravity data that have been collected through dedicated gravity campaigns. These were focused not only around the CORS stations but also targeted the entire area of RCM. The gravity observations have been carried out with the CG5 gravity meter relative to absolute gravity stations established using the A10 (#027) absolute gravity meter. The development of the geoid was based in the classical Remove-Compute-Restore (RCR) technique and an FFT-evaluation of Stokes’ integral. The long and short wavelengths of the gravity field spectrum were removed from the available input gravity data, then prediction of the residual geoid was carried out and finally the effects removed have been restored to derive the final model. To model the long-wavelength part of the spectrum, XGM2019e has been used as reference while the topographic effects were evaluated based on a spherical harmonics expansion of the Earth’s potential and ultra-high resolution residual terrain correction (RTC) effects from a global model. The prediction of the geoid model was carried out using the classical 1d-FFT spherical Stokes convolution with the Wong-Gore modification for the Stokes kernel and 100% zero-padding in all directions. Various tests against available collocated GNSS/Leveling observations have been performed to find the optimal cut-off degree while the evaluation of the model was carried out over 533 geodetic benchmarks in the entire study area, where accurate static GNSS observations and orthometric heights from the Hellenic Military Geographic Service (HMGS) were available.

How to cite: Vergos, G. S., Natsiopoulos, D. A., Tzanou, E. A., Mamagiannou, E. G., Triantafyllou, A. I., Tziavos, I. N., Ramnalis, D., and Polychronos, V.: A regional gravimetric geoid model in support of the GeoNetGNSS CORS network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13423, https://doi.org/10.5194/egusphere-egu23-13423, 2023.

Geodesy defines a physical height as the shortest distance of a point to a height reference surface in the Riemannian physical space. Two types of physical heights are most commonly used in science and applications, namely orthometric and normal heights. Both heights use the same reference surface (geoid) but differ in metrics associated with either the real (in case of orthometric heights) or model (for normal heights) gravity field. Orthometric heights correspond to the classical concept of physical heights introduced in the 19th century by Gauss, Stokes and Helmert. The main reason for introducing normal heights in the mid-20th century by Vignal and Molodensky, was related to a fact that the metric for orthometric heights (or corresponding gravity corrections to levelled height differences) could be estimated only approximately as they depend on the topographic mass density. Consequentially, normal heights have been introduced in many countries worldwide. However, their concept is sometimes misunderstood as the quasi-geoid is incorrectly referred to as their reference surface. Physical heights and corresponding height systems were discussed at the 10th Hotine-Marussi Symposium held in Milan, June 2022. A motion was proposed and discussed at the symposium that acknowledged reported problems of the quasi-geoid and its improper use as a height reference surface in geodesy. This presentation summarizes main arguments that were used to forge the motion. 

How to cite: Novak, P. and Sansò, F.: On the correct definition and use of normal heights in geodesy  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17520, https://doi.org/10.5194/egusphere-egu23-17520, 2023.

The International GNSS Service (IGS) analysis centers (ACs) for the third time issued the results of the reprocessing campaign (IGS Repro3) of all the GNSS network solutions backward starting from 1994. The Repro3 products provided the IGS contribution to the latest International Terrestrial Reference Frame realization ITRF2020. Unlike the previous reprocessing campaigns, the IGS Repro3 includes for the first time not only GPS and GLONASS but also the Galileo constellation. 

In this study, we show results from the GLONASS and Galileo orbit validation of different IGS ACs, as well as the combined orbits generated by the IGS Analysis Centre Coordinator (IGS ACC) at Geoscience Australia. Individual multi-GNSS orbit solutions were provided by Center for Orbit Determination in Europe (COD), European Space Agency (ESA), GeoForschungsZentrum (GFZ), Centre National d’Études Spatiales (GRG), Graz University of Technology (TUG) and Massachusetts Institute of Technology (MIT). Different IGS ACs use different orbit modeling strategies, e.g., estimating specific empirical orbit parameters and using or not using the a priori box-wing models for the Galileo satellites. The individual IGS Repro3 contributions have been combined by the IGS ACC combination software using a robust algorithm and a satellite-based weighting approach considering different qualities of GNSS orbits provided by different IGS ACs. We summarized the recent progress in GNSS precise orbit determination focusing on the impact of the orbit modeling aspects on the systematic effects in the SLR validation results, e.g., solar radiation pressure modeling and observable types.

For all the defined Galileo and GLONASS satellite subtypes, the combined solutions do not perform worse (to the 1 mm level) than the best individual AC solutions for a specific satellite type. In terms of the standard deviation of SLR residuals, ESA, MIT, and TUG deliver the best Galileo-FOC orbits and ESA provides the best Galileo-IOV orbit solutions. Finally, ESA and TUG provide the best GLONASS products. Searching for patterns in SLR residuals for different satellite-Sun-Earth geometries reveals that some issues in the orbit modeling for the Galileo-FOC and IOV satellites still need to be fully diminished. The pattern dominates in COD, GFZ, and GRG solutions, and is mostly diminished in ESA and TUG solutions. The characteristic pattern is also noticeable in the combined solutions, but with a reduced magnitude. 

How to cite: Zajdel, R., Sośnica, K., Masoumi, S., Bury, G., and Strugarek, D.: SLR validation of the IGS Repro3 orbits for ITRF2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-455, https://doi.org/10.5194/egusphere-egu23-455, 2023.

The Copernicus Precise Orbit Determination (CPOD) Service is a consortium led by GMV, responsible for providing precise orbital products and auxiliary data files from the Copernicus Sentinel-1, -2, -3, and -6 missions to the corresponding Payload Data Ground Segment (PDGS) processing chains at ESA and EUMETSAT.

Since April 2014, the CPOD Service has been supporting the Copernicus program as soon as the different Sentinel satellites were launched. During the last 8 years, the CPOD Service has been using the ESA/ESOC SW NAPEOS, to compute the precise orbits. During these years, new algorithms and standards were implemented in NAPEOS, to improve the accuracy of the products. Currently, the accuracy of the orbital solutions computed by the CPOD Service is state-of the art, and similar to the solutions computed by other entities including AIUB, CNES, DLR, ESA, GFZ, JPL, TU Delft, and TUM, all of them members of the CPOD Quality Working Group (QWG).

Starting on January 2021, GMV has been developing a new POD SW called FocusPOD, as an internal R&D activity. Following current trends (e.g., GIPSY-X, GODOT), FocusPOD has been written from scratch in C++ & Python, with a completely new design, with the goal of supporting future CPOD Services evolutions, among other projects.

In terms of architecture, the core layers of the FocusPOD SW have been designed as a library, to support a flexible development of applications. For example, constructing multiple distributed programs is possible, as well as building a single binary that decodes the GNSS L0 data, reads the different input files (e.g., GNSS orbits and clocks), pre-processes the observations, propagates the initial state vector, performs the least-square adjustment, fixes ambiguities, and constructs the final product; all with a single execution that allows reducing the processing time and minimizes the usage of HW resources. The functionality of each binary may be constructed as needed.

One of the key differences with respect to the previous SW is the decision to separate data and algorithms in the design of FocusPOD. This has triggered the development of a data model to keep in the processing memory all the data, organized following its physical meaning, and relating different elements. This will allow developing new algorithms independently of the data. Another relevant aspect is the use of advanced mechanisms to keep and search large amounts of data, a key element to exploit the SW in future use cases.

The architecture of FocusPOD will be presented, as well as its performance. In terms of architecture, the benefits of the chosen design will be highlighted together with the lessons learnt from the implementation. In terms of performance, it will be shown that the new SW presents improvements in runtime with respect to the legacy system, reducing the product generation timeliness, while reaching the same levels of accuracy as other state-of-the-art SW packages. The achievable accuracy in LEO POD will be presented by showing the differences against external reference solutions and SLR residuals analysis of the Sentinel satellites.

How to cite: Fernández Martín, C., Berzosa Molina, J., Bao Cheng, L., Muñoz de la Torre, M. Á., Fernández Usón, M., Lara Espinosa, S., Terradillos Estévez, E., Fernández Sánchez, J., Peter, H., Féménias, P., and Nogueira Loddo, C.: FocusPOD, the new POD SW used at CPOD Service, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1908, https://doi.org/10.5194/egusphere-egu23-1908, 2023.

Low Earth orbit (LEO) satellites are widely used in space missions such as satellite gravimetry, radio occultation, Earth monitoring, and in formation flying. Precise orbit determination (POD), in either absolute or relative modes, is an essential prerequisite for these missions. The onboard collected signals of the global navigation satellite system (GNSS) are used for the POD of LEO satellites. Typically, the Ionosphere-free (IF) combination of these signals is used in the absolute LEO POD, which has some disadvantages. Firstly, the observation information is wasted in constructing IF observation. Secondly, although different IF combinations can be constructed in multi-frequency scenarios, they may be correlated. Thirdly, integer ambiguity resolution (IAR) based on the IF observations can only be achieved with precise external products, which has limited availability in space. Concerning relative POD, the most classical method is the double-differenced (DD) model with IAR, which also has drawbacks. Firstly, strict common-view GNSS satellites are needed, which is not guaranteed in the complex space environment with the high dynamic of the satellites. Secondly, the opportunity to impose dynamic constraints on the eliminated parameters is lost during differencing. Therefore, in this contribution, we focus on the use of undifferenced uncombined (UDUC) observations and propose a new POD model. The UDUC POD model has several advantages. Firstly, the common-view GNSS satellites are only used to form the DD ambiguities for IAR; therefore, there is no need for the external satellite phase bias (SPB) products. Secondly, the model shows flexibility in multi-frequency scenarios. Thirdly, and more importantly, as precise GNSS orbits and clocks products are used, the model can be used for both absolute and relative LEO POD. Based on onboard GPS observations of a formation flying mission, comprising two closely spaced LEO satellites working in a formation, we explored the performance improvement of the proposed model over traditional models. Two conclusions can be drawn. Firstly, the proposed model's performance in absolute POD is improved by more than 20% compared with the classical IF POD method, when computing their differences with reference orbits. Secondly, for relative POD, it is proposed that the consistency between the model and the reference orbit is within 1.5 mm, proving that the method can serve for formation flying missions. The above results show that the proposed UDUC POD method can achieve higher POD accuracy than the traditional methods.

How to cite: El-Mowafy, P. A.: Undifferenced and uncombined GNSS approach for absolute and relative POD of LEO satellites in formation flying, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2576, https://doi.org/10.5194/egusphere-egu23-2576, 2023.

Along with other space geodetics, the Global Navigation Satellite Systems (GNSS) technique has a profound impact on the realization of terrestrial reference frames and the provision of geodetic and geophysical parameters such as Earth Rotation Parameters (ERP) and geocenter (GCC) coordinates. In GNSS data processing ambiguity resolution (AR) is critical to achieve high-precision estimates. Due to the uncalibrated phase delay (UPD), currently most International GNSS Service (IGS) Analysis Centers (ACs) adopt the double-differenced (DD) ambiguity resolution strategy, which eliminates UPD by between-satellite and between-station differencing. Undifferenced (UD) ambiguity resolution, which recovers the integer characteristics of the UD ambiguities by directly estimating the UPD, was originally developed for Precise Point Positioning and nowadays is also applied to network processing, for example for Precise Orbit Determination (POD). In this study, we conducted a comparative study on the UD and DD ambiguity resolution for GNSS POD data processing. We demonstrated that the UD strategy significantly improves the solution compared to the DD solutions. The GPS orbit precision is improved by 20%, 12%, and 5% in the along, cross, and radial component, respectively. Moreover, the ERP are significantly improved, and the agreement with the IGS final products is improved by 28% and 23% for the offsets of x-pole and y-pole, respectively, and by 23%, and 17% for the corresponding rates. Additionally, the repeatability of station coordinates and GCC coordinates is also slightly improved. More important, we confirmed that the two strategies are theoretically equivalent and the outperformance of UD strategy could be explained by its strong robustness to wrong-fixings and its capability to fix the most UD ambiguities, while wrong-fixings and missing fixings are hardly avoidable in the DD strategy due to the requirement of forming DD-ambiguities.

How to cite: Tang, L., Wang, J., Nie, L., Zhu, H., Ge, M., and Schuh, H.: Improving GNSS data analysis with undifferenced integer ambiguity resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3589, https://doi.org/10.5194/egusphere-egu23-3589, 2023.

Precise orbit knowledge is a fundamental requirement for low Earth orbit (LEO) satellites. Accurate non-gravitational force modeling directly improves the overall quality of LEO precise orbit determination (POD). Time-dependent radiation data and modeled physical effects are considered to address the potential approximation errors in solar radiation pressure (SRP) modeling. We develop an advanced thermal reradiation model for satellite solar panels. A set of improved non-gravitational force models is performed for LEO POD, and we discuss the benefits of the enhanced dynamic models on orbit quality and dependence on empirical parameters. The Gravity Recovery and Climate Experiment Follow-On (GRACE-FO), Jason-3, and Haiyang-2B missions are selected for the POD process. Estimated empirical acceleration and scale parameters and independent satellite laser ranging (SLR) are used to validate the final orbit solutions. The magnitude of empirical acceleration estimated in POD is reduced by 19% with the enhanced dynamic modeling, and the estimated scale factor for the SRP converges to stable and reasonable level. Furthermore, the steady-state temperature model used in thermal reradiation can effectively reduce mismodeled effects in the SRP, and the systematic linear dependency revealed by the SLR residuals is significantly reduced for the GRACE-C and Jason-3 satellites, with improvements of approximately 61% and 49%, respectively. With the enhanced non-gravitational force models, the SLR validation shows the best orbit solutions with RMS values of 10.4, 10.1, 12.4, and 13.2 mm for the GRACE-C, GRACE-D, HY-2B, and Jason-3 satellites, respectively. Overall, advances are made in the explicit modeling of non-gravitational forces to pursue superior satellite orbits, suggesting a more dynamic orbit solution.

How to cite: Li, M., Wang, Y., Jiang, K., Li, W., Zhao, Q., Fang, R., Wei, N., and Mu, R.: Enhanced solar radiation pressure modeling for LEO precise orbit determination: result validation and improvement, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4244, https://doi.org/10.5194/egusphere-egu23-4244, 2023.

Over the last years, ideas of installing a dedicated Very Long Baseline Interferometry (VLBI) transmitter on board of the second generation of Galileo satellites have been proposed. The mounting of such a transmitter on future satellites raises scientific questions and opens new opportunities of extending the current VLBI research with observations to geodetic satellites. These observations allow combining the satellite and the quasar frame due to the unique opportunity of determining the satellite orbit in the International Celestial Reference Frame (ICRF).

In this contribution, we present the estimation of orbit arcs based on VLBI observations combined with GNSS measurements. For this purpose, schedules including satellite and quasar observations, are created with the scheduling software VieSched++. These schedules are simulated and analyzed with the Vienna VLBI and Satellite Software (VieVS). In the analysis the partial derivatives of the state vector of the satellite with respect to the orbital elements, obtained from the module ORBGEN in Bernese, are used in VieVS for calculating the partial derivatives of the time delay with respect to the orbital elements. This approach allows to estimate the orbital elements from simulated VLBI observations. The quality of the estimated parameters is investigated and assessed based on the mean formal errors and the repeatabilities.
In a further step there is the option to combine the results from VieVS and Bernese at the normal equation (NEQ) level using the ADDNEQ2 and retrieve fully consistent orbital parameters based on VLBI and GNSS observations.

How to cite: Wolf, H., Böhm, J., and Hugentobler, U.: Estimating orbital elements from VLBI observations and GNSS measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4881, https://doi.org/10.5194/egusphere-egu23-4881, 2023.

The Gravity Recovery Object Oriented Programming System (GROOPS) is meanwhile a highly sophisticated and well accepted tool in the scientific community which enables the user to perform core geodetic tasks. The key features of the software include gravity field recovery from satellite and terrestrial data, the processing of global navigation satellite system (GNSS) constellations and ground station networks and the determination of satellite orbits from GNSS measurements. In the course of the continuous development of GROOPS, we will extend the software by satellite laser ranging (SLR) as an additional feature. Satellite laser ranging offers the possibility to measure distances from low earth orbiting (LEO) satellites with an accuracy in the mm and cm range. A major advantage of this observation technique is that only a passive space technology, called laser retroreflectors are required onboard. Satellite laser ranging can be used as a tool for independent validation of precise determined LEO satellite orbits. Thus, through the extension of GROOPS by SLR we will also be able to perform a validation of our own determined satellite orbits, which we publish regularly. In this work we will give an overview of the integration of the SLR processing, and how corrections regarding the satellites centre of mass, antenna offsets, laser retroreflector offsets and satellite/station specific range biases are handled. Additionally, we will show the orbit validation results of several satellite missions with laser retroreflectors onboard.

How to cite: Suesser- Rechberger, B., Mayer-Guerr, T., Dumitraschkewitz, P., Tieber-Hubmann, C., and Krauss, S.: Extension of the software toolkit GROOPS by satellite laser ranging, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5244, https://doi.org/10.5194/egusphere-egu23-5244, 2023.

The European Space Agency (ESA) Swarm mission was launched in November 2013 and consists of three identical satellites flying in near-polar low Earth orbits to study the dynamics of the Earth’s magnetic field. In the Swarm Data, Innovation, and Science Cluster framework, precise science orbits (PSO) are computed for the Swarm satellites from onboard GPS observations. These PSO consist of a reduced-dynamic orbit to precisely geotag the magnetic and electric field observations, and a kinematic solution with covariance information, which can be used for determining large-scale time variable changes of Earth’s gravity field. In addition, high-resolution thermospheric densities are computed from onboard accelerometer data. Due to accelerometer instrument issues, these data are currently only available for Swarm-C and the early mission phase of Swarm-A. Therefore, also GPS-derived thermospheric densities are computed, which have a lower temporal resolution but are available for all Swarm satellites during the entire mission. The Swarm density data can be used to study the influence of solar and geomagnetic activity on the thermosphere.

We will present the current status of the processing strategy used to derive the Swarm PSO and thermospheric densities and show recent results. For the PSO, our processing strategy includes a realistic satellite panel model for solar and Earth radiation pressure modelling, integer ambiguity fixing, and a screening procedure to reduce the impact of ionospheric scintillation-induced errors. Validation by independent Satellite Laser Ranging data shows the Swarm PSO have high accuracy, with an RMS of the laser residuals of about 1 cm for the reduced-dynamic orbits, and slightly higher values for the kinematic orbits. For the thermospheric densities, our processing strategy includes a high-fidelity satellite geometry model and the SPARTA gas-dynamics simulator for gas-surface interaction modelling. Comparisons between Swarm densities and NRLMSIS model densities show noticeable scaling differences, indicating the Swarm densities' potential to contribute to thermosphere model improvement. The accuracy of the Swarm densities is dependent on the aerodynamic signal size. For low solar activity, the error in the radiation pressure modelling becomes significant, especially for the higher-flying Swarm-B satellite.

The Swarm precise orbit and thermospheric density products are available for users at the dedicated ESA Swarm website (ftp://swarm-diss.eo.esa.int). The Swarm densities are also available at our thermospheric density database (http://thermosphere.tudelft.nl). This database also includes thermospheric densities for the CHAMP, GRACE, GOCE, and GRACE-FO satellites. For future work, it is planned to further improve the Swarm densities, especially for low solar activity conditions, by including a more sophisticated radiation pressure modelling of the Swarm satellites.

How to cite: van den IJssel, J., Siemes, C., and Visser, P.: Precise science orbits and thermospheric densities for the Swarm mission, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5432, https://doi.org/10.5194/egusphere-egu23-5432, 2023.

In the framework of the European Space Agency’s Moonlight program, a satellite navigation system is planned for positioning, navigation, timing, and communication on the Moon.  The constellation will consist of three or four lunar orbiters in eccentric orbits – with periselene above the northern hemisphere and aposelene above the southern hemisphere; the latter is of special interest in terms of future lunar missions. The eccentric orbits introduce a challenge for precise orbit determination, because large gravity perturbations due to the lunar gravity field occur in the periselene passes, whereas the aposelene passes are associated with the smallest gravity gradients and thus the largest errors in orbit determination.

We evaluate the non-gravitational and gravitational perturbing forces acting on lunar orbiters in eccentric orbits. The simulated orbits consider lunar gravity field based on the GRAIL mission, gravity perturbations from the Sun, Earth, and planets considering Earth’s oblateness, tidal deformations, direct solar radiation pressure with lunar and Earth eclipses, albedo, antenna thrust, and relativistic effects. We discuss three methods of proposed representation of the broadcast orbits: based on Keplerian parameters and a set of one-per-revolution corrections (GPS-like or Galileo-like), based on Chebyshev polynomials with a variable number of coefficients and arc-length representation, and based on a series of positions and velocities (GLONASS-like). We discuss the advantages and limitations of all three representations and accuracies provided by different approaches depending on the number of assumed coefficients and arc lengths. Finally, we discuss the impact of inconsistent treatment of the origin, scale, and orientation of the lunar reference frame on the determined positions on the Moon. 

How to cite: Sośnica, K., Zajdel, R., Bury, G., Di Benedetto, M., Durante, D., Sesta, A., Fienga, A., Linty, N., Belfi, J., and Iess, L.: Precise orbits for the lunar navigation system: challenges in the modeling of perturbing forces and broadcast orbit representation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5575, https://doi.org/10.5194/egusphere-egu23-5575, 2023.

The accuracy and availability of real-time precise orbits are critical for real-time Global Navigation Satellite Systems (GNSS) users. Real-time orbits are estimated by either batch processing using least-squares adjustment at most International GNSS Service (IGS) Analysis Centers (ACs), or filter-processing, for example, at JPL and Wuhan University. The filter-processing has the advantage of high-update rates from 5 min to 5 sec (in the case of real-time clock), which is more suitable to handle satellite maneuvers. Currently, maneuver satellites are labelled as unhealthy in broadcast ephemeris, and not processed by the IGS ACs. However, for the robustness and availability of real-time GNSS users, it is important to provide reliable orbits and clocks for as many satellites as possible, especially for some special scenarios such as poor visibility of low-elevation satellites in canyon or urban areas. Moreover, if the satellite maneuver is not handled in time, it could severely deteriorate the orbit quality of all satellites. In this study, we implement the square root information filter (SRIF) for real-time GNSS orbit determination to achieve an update rate of 30 sec. We propose an automatic method to detect the satellite maneuver and adjust the stochastic constraints of orbital elements. The constraints applied to the epoch-wise orbital elements, which are essential for the SRIF-based POD, are checked based on its post-fit residuals and adjusted accordingly. Using the simulated real-time processing of GPS satellites during six months in 2022, we demonstrate that the satellite maneuver can be successfully detected instantaneously without degrading the accuracy of any satellites. Comparison with the 5 min sampling final orbit products from Center for Orbit Determination in Europe (CODE), there is no loss of accuracy in the along and cross components and the agreements is within 5 cm. In the radial component, the orbit difference is around 5 dm during the first one to two hours after the maneuvering, and the orbit accuracy converges to 5 to 10 cm after 4 hours. Due to the correlation between radial orbit and satellite clock, it is validated by the phase residuals of static precise point positioning (PPP) that such an accuracy causes no degradation to the positioning users. In addition, we evaluate the important contribution of rescued maneuver satellites using kinematic PPP under various simulated observing scenarios.

How to cite: Qin, Z., Wang, J., Tang, L., Du, S., Huang, G., Zhang, Q., Ge, M., and Harald, S.: Filter-based Real-time GNSS Precise Orbit Determination Applied to Satellites in Maneuver, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6285, https://doi.org/10.5194/egusphere-egu23-6285, 2023.

The absolute positional accuracy of altimetry satellites is one key aspect for subsequent analyses in Earth observation. To determine the position of a satellite with highest accuracy, various observation techniques are obtainable. Recent satellites like the Copernicus Sentinel-3A/3B and 6A Michael Freilich (MF) satellites are equipped with multiple observation techniques onboard. We use the techniques Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Global Positioning System (GPS) and Satellite Laser Ranging (SLR) to generate orbits based on DORIS-only, on the combination of DORIS and SLR, and on GPS-only. To examine the accuracy of the orbits, we compare them inter-technique-wise and with an external combined orbit solution, which is assumed to have superior absolute accuracy and minimal residual systematic errors. Subsequently, we strive to generate reference frame realizations for the DORIS technique in order to be able to contribute an additional solution to the International DORIS Service (IDS) in the future. Therefore, we use the DORIS only-orbit solutions, and generate weekly local reference frames for each of the three satellites and in combination. We evaluate these based on the reference frame defining parameters, i.e. origin, scale and orientation.

How to cite: Schreiner, P., Reinhold, A., Neumayer, K. H., and Koenig, R.: Sentinel POD based on DORIS, GPS and SLR and subsequent reference frame determination based on DORIS-only, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6489, https://doi.org/10.5194/egusphere-egu23-6489, 2023.

Precise non-gravitational force models are crucial for satellite gravimetry, thermospheric neutral density estimation, and precise orbit estimation (POD). Besides the dominating aerodynamic acceleration acting on low Earth orbit satellites, radiation pressure accelerations impact their motion. The acceleration due to the Earth radiation pressure (ERP) decreases with increasing satellite altitude, whereas the effects of the Solar radiation pressure (SRP) and thermal reradiation pressure (TRP) vary mainly with the satellite’s orientation towards the Sun.

In previous investigations, we extended the existing radiation pressure force models with a focus on a GRACE-like satellite. However, validating the non-gravitational force modelling remained difficult. For GRACE and GRACE-FO, a comparison to measured accelerometer data is possible. However, it is obviously difficult to separate residual effects of the necessary accelerometer calibration procedure from errors in the radiation pressure models.

To overcome these disadvantages, here we perform a validation of modelled non-gravitational accelerations using independent satellite laser ranging (SLR) measurements, which do not require such calibration. This approach is twofold. In a first step, a POD is performed, where kinematic GNSS-orbits and modelled non-gravitational accelerations serve as input together with gravitational state-of-the-art background models. Second, the residuals between the SLR measurements and the derived orbit are computed. Since we assume the SLR observations as the truth, small residuals indicate that the modelled non-gravitational accelerations represent reality well. A comparison against GNSS orbit solutions is not performed here, since kinematic orbits are already part of the first step and the comparison would not be independent.

We choose the year 2008 for our experiments, where the radiation pressure signal is at the same order of magnitude as the aerodynamic signal. Our two-fold approach is performed several times, where we vary the parametrization of the radiation pressure force model, e.g., the consideration of the Earth’s radiation data sets or the satellite’s thermal reradiation. The aerodynamic model is kept fixed during these experiments and a scale factor for this force is co-estimated to account for its mismodelling. Our preliminary results indicate that the smallest residuals occur when considering non-instantaneous TRP acceleration with modified material (diffusion) parameters in addition to our extended ERP and SRP force models. In this case, the annual RMS per pass of the residuals is 2.72cm, which is 2.4cm below the results obtained with standard models and still nearly 4mm less than without modifying the TRP parameters.

How to cite: Vielberg, K., Löcher, A., and Kusche, J.: Validating radiation pressure force models for GRACE with SLR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6533, https://doi.org/10.5194/egusphere-egu23-6533, 2023.

The Combination Service for Time-variable Gravity fields (COST-G) provides models of the time-variable Earth gravity field that may be used for precise orbit determination (POD). While the monthly snapshot solutions based on GRACE or GRACE-FO GPS and microwave ranging interferometer data are the best available information on the time-variable gravity field, their latency of about 2-3 months prevents their use in operational POD. COST-G also provides a signal model fitted to the monthly GRACE-FO gravity fields that is updated quarterly and allows for the prediction of time-variable gravity, e.g. for use in applications that rely on short latency like operational POD.

We present POD results for LEO and MEO satellites based on the COST-G fitted signal model (FSM), where we put special attention on the impact of the C₂₀ gravity field coefficient, which is poorly defined from the GRACE/GRACE-FO observations, but may be replaced by SLR-only or SLR+GRACE/GRACE-FO combined solutions. We moreover present an extension of the COST-G FSM, also covering the GRACE-period and therefore suited for reprocessing campaigns that rely on a consistent model of time-variable gravity.

How to cite: Meyer, U., Peter, H., Geisser, L., Calero, E., Dach, R., and Jäggi, A.: COST-G models of time-variable gravity for precise orbit determination, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6553, https://doi.org/10.5194/egusphere-egu23-6553, 2023.

Co-location in space is an alternative combination strategy of the four main space geodetic techniques. All four of them, namely DORIS, GNSS, SLR, and VLBI, currently contributing to the determination of the terrestrial reference frame (TRF) can be combined using a so-called space-tie satellite, ideally equipped with receivers and/or transmitters for all of the techniques. The early GRASP and E-GRASP satellite mission proposals to NASA and ESA had not been recommended for the next phase, but recently, the GENESIS mission got green light from ESA which opens a unique opportunity for geodesy. We perform simulations and subsequent precise orbit determination (POD) of all four space geodetic techniques and solving also for the TRF, and combine them at one satellite using the space tie. Real data analysis including POD to prominent satellite missions like LAGEOS, TOPEX, and Sentinel-6A MF was done for most realistic simulations. In particular, the impact of biased space ties is investigated in terms of 14-parameter Helmert transformations compared to a perfect modeling solution. We will also present first simulation results of the GENESIS mission.

How to cite: Glaser, S., Schreiner, P., Mammadaliyev, N., König, R., and Schuh, H.: On the opportunities of co-location in space for envisaged space-tie satellite missions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6632, https://doi.org/10.5194/egusphere-egu23-6632, 2023.

A global Terrestrial Reference Frame (TRF) is realized today by four space geodetic techniques, i.e., Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), Very Long Baseline Interferometry (VLBI), and Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS). The current goals for the TRF realization are specified with an accuracy of 1 mm and long-term stability of 0.1 mm/year according to the Global Geodetic Observing System requirements.

Differences in the characteristics of each space geodetic technique might introduce systematic effects into TRF realization. Among the crucial systematics, we can distinguish modeling and calibration deficiencies, i.e., direct solar radiation pressure (SRP) modeling for GNSS and DORIS, GNSS antenna calibration uncertainties, South Atlantic Anomaly handling for DORIS, and time and range bias handling for SLR. The current realization of the TRF is based on independent solutions for each of the four contributing space geodetic techniques that are just connected on the ground via local ties and the Earth Rotation Parameters. A new opportunity to challenge the systematic errors is to co-locate space techniques onboard one satellite, as it is planned for the Genesis-1 mission. The Genesis-1 satellite is the first ever satellite co-locating sensors related to GNSS, SLR, DORIS, and VLBI.

In this study, we present preliminary results for orbit reconstruction using simulated GNSS observations for the Genesis-1 satellite. We use the Bernese GNSS Software for different orbital altitudes, including the currently planned altitude of 6000 km. We assess the quality of the orbit reconstruction using simulated GNSS data from observations of the zenith-, nadir-, and both zenith and nadir-looking antennas. Additionally, we assess the visibility from the ground tracking network of VLBI, SLR, and DORIS, for the different satellite altitudes.

How to cite: Bury, G., Arnold, D., Dach, R., and Jäggi, A.: Simulation of GNSS observations for Genesis-1, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7927, https://doi.org/10.5194/egusphere-egu23-7927, 2023.

The Galileo for Science Project (G4S_2.0) is an ongoing project funded by the Italian Space Agency that has several goals in the field of Fundamental Physics by exploiting the Galileo-FOC Constellation and, in particular, GSAT-0201 and GSAT-0202, the two FOC in elliptical orbit. The high eccentricity of their orbits and the accuracy of their atomic clocks allow to measure gravitational redshift and relativistic precessions of the orbits. These results will place new constraints on possible alternative theories of gravitation, both metric and non-metric in their structure. Furthermore, constraints on the presence of Dark Matter in our Galaxy can be placed by analysing data of the satellites’ atomic clocks.

In this framework a fundamental point is obtaining a suitable satellite orbit solution by performing an accurate Precise Orbit Determination (POD). To this purpose modeling, as better as possible, the complex effects of the Non-Gravitational Perturbations (NGPs) is essential. In particular, the direct Solar Radiation Pressure (SRP) represents the main source of error in determining the orbit of any GNSS spacecraft, as it is the largest NGPs perturbation.

Our final goal is to build a refined Finite Element Model (FEM) of the Galileo FOC spacecraft to compute the perturbing accelerations that will be used in the POD procedure.

As an intermediate step a Box-Wing (BW) model, as well as a 3D-CAD of the spacecraft, have been developed. We will present the results for the perturbing accelerations produced by SRP, Earth’s infrared radiation and Earth’s albedo in the case of a BW model built using the ESA Galileo metadata.

Moreover, accounting for multiple reflections and mutual shadowing effects is crucial to improve the POD and the scientific results. To this purpose we apply the so-called Ray Tracing technique to the spacecraft FEM. We will present our ongoing work on this technique by using the software COMSOL and Matlab on the current development we obtained for the FEM.

Finally, by using the residuals in the orbital elements obtained from a POD, we can test our new models and the improvements in the quality of the POD. In order to prove the reliability and robustness of the scientific results that will be obtained within G4S_2.0, we aim to exploit both GEODYN II and the Bernese software for the POD.

How to cite: Sapio, F., Lucchesi, D., Visco, M., Lefevre, C., Cinelli, M., Di Marco, A., Fiorenza, E., Loffredo, P., Lucente, M., Magnafico, C., Peron, R., Santoli, F., Gatto, N., and Vespe, F.: The Galileo for Science project: Precise Orbit Determination and force-modeling for the Galileo FOC satellites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8840, https://doi.org/10.5194/egusphere-egu23-8840, 2023.

The precision of the GNSS positioning depends on the accuracy and stability of the GNSS satellite orbits. Indeed, the analysis of the GNSS precise orbits determined by the IGS analysis centers shows different long-term behavior in the eccentricities and inclinations of GPS satellites, compared to GLONASS and Galileo satellites. This contribution focuses on analyzing sources of long-term dynamics in the GNSS orbits, particularly in the GPS orbits, and the influence of the constellation design. We investigate orbital resonances resulting from external accelerations such as lunisolar gravitation by semi-analytical simulations and compare the dynamical response of the four available constellations: GPS, Galileo, GLONASS, and BeiDou. Finally, we assess the impact of this different dynamical behavior on Precise Point Positioning (PPP).

How to cite: Ait-Lakbir, H., Santamaría-Gómez, A., Perosanz, F., and Ray, J.: Comparison and analysis of the long-term dynamics of GNSS orbits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11231, https://doi.org/10.5194/egusphere-egu23-11231, 2023.

In order to increase the accuracy of precise orbit determination for a single satellite or satellites in LEO formation, we propose using a LEO-to-GNSS laser interferometer, what we call a “laser GNSS receiver”, to measure the Doppler shift with a continuous-wave (CW) laser between LEO and GNSS satellites equipped with SLR arrays (Galileo, GPS, GLONASS, Beidou). LEO orbit is above atmosphere (no  atmospheric attenuation and turbulence in laser signal) and this makes the “laser GNSS receiver” very attractive for future LEO missions. At the EGU and AGU conferences, over the last several years, we have presented the link budget, design and feasibility of such a new instrument in space geodesy and discussed applications in: reference frame missions; gravity field missions; laser atmospheric sounding (above the clouds) and combination with microwave GNSS-RO; time/frequency transfer for ground optical clocks at 10^-18 frequency uncertainty (TAI, UTC); and Earth-to-Moon laser interferometry using an ILRS telescope. Here we extend this new instrument in space geodesy to laser DORIS and laser SAR.

Laser altimetry is an established technique that uses a pulsed laser to measure a range from LEO orbit to the ground in the nadir direction. In a similar way, interferometric laser tracking could be established on the continuous-wave laser signal transmitted from the LEO orbit in the nadir direction and reflected from the ground. This could be done, e.g., by modulating a microwave-like signal on a CW laser, providing a microwave phase on a laser carrier. The main advantage of the laser SAR/inSAR is that microwave modulation on a laser carrier is not going to be affected very much by the wet delay of the atmosphere and in this way does not require radiometers in LEO to correct atmospheric propagation effects, and instead, they can be corrected a priori using models like those used for the SLR measurements.

Therefore, compared to the microwave SAR/inSAR, laser SAR/inSAR opens up the possibility of using the SAR/inSAR technique along with space geodesy techniques if permanent geodetic stations are equipped with the well-defined laser retro-reflectors on the ground. Compared to the pulsed lasers used by ILRS, a continuous-wave laser is more appropriate for higher laser powers since the lower laser peak power avoids damage to the transmitting optics and allows simplified optics with non-mechanical laser beam steering. We present link budget of such a laser DORIS technique to observe Doppler shift from LEO orbit to the ground laser retro-reflectors and laser SAR/inSAR based on laser signal reflected from the ground surface. The IceSAT-2 mission from NASA indirectly confirmed the link budget with the onboard pulsed laser used for laser altimetry, opening up the possibility of a laser SAR/inSAR technique from LEO.

How to cite: Svehla, D.: LEO-to-GNSS Laser Interferometer for Space Geodesy with Laser DORIS and Laser SAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11867, https://doi.org/10.5194/egusphere-egu23-11867, 2023.

Precise orbit determination (POD) of low earth orbiters (LEO) using data of the Global Positioning System (GPS) and the computation of GPS network solutions are usually performed in separate processes. Typically, orbits and clock corrections of GPS satellites, which have been previously determined as part of a network solution, are introduced as fixed in a LEO POD. However, various studies have shown that the inclusion of GPS observations of LEOs in a global network solution can be advantageous, particularly in terms of the quality of resulting GPS products and certain geodetic parameters, such as the Earth’s center of mass coordinates. Since a few years more and more GPS data from LEO CubeSats are available, such as from the SPIRE satellites which are equipped with dual-frequency GPS receivers and may be used as part of specific scientific investigations. The SPIRE satellite constellation is a group of remote sensing satellites that are used to measure and map the earth's surface and atmosphere.

In the present study, we aim to determine the impact of GPS observation data from specific SPIRE satellites when they are included in the computation of a global network solution. Code and phase observations received by GPS receivers on board of selected SPIRE satellites, along with those from ground stations of the International GNSS Service (IGS), are processed together in a joint least-squares adjustment process to obtain a combined GPS-LEO solution. This determines orbit parameters of the SPIRE satellites together with GPS orbit parameters and geodetic parameters, such as station coordinates, Earth rotation parameters, and the Earth's center of mass coordinates. To assess the influence of the SPIRE LEOs more closely, various solutions are analyzed in which GPS observations from different SPIRE satellites and from scientific LEO missions are included. Given the different orbit characteristics of the selected SPIRE satellites, specifically the orbital inclinations, it is also possible to examine the impact of this on the resulting solution. The global solutions are compared to each other and to a solution using only data from terrestrial GPS stations. Quality characteristics are analyzed to assess the quality of the combined GPS-LEO solution, which are the resulting GPS orbit solutions in terms of orbit overlaps at arc boundaries, the quality of geodetic parameters, and the determined formal errors of the estimated parameters. The resulting SPIRE orbits of the combined solutions are also compared to those of a separate POD.

How to cite: Kobel, C., Arnold, D., and Jäggi, A.: Impact of incorporating SPIRE CubeSat GPS observations in a global GPS network solution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12153, https://doi.org/10.5194/egusphere-egu23-12153, 2023.

We discuss a concept of probabilistic orbit. If correctly constructed, an ensemble of equally plausible orbits is a proper representation of the underlying true and unknown probability distribution of orbits. Hence, the probabilistic orbit is determined by the entire sample and its statistical properties rather than any individual ensemble member. We explore the concept by starting from an ensemble of atmospheric state estimates generated at ECMWF (N=51). The ensemble mean closely corresponds to the most likely atmospheric state estimate, and the ensemble spread to its inherent uncertainty. We compute separately a GNSS orbit solution for each unique atmospheric state (N=51). Thus, we essentially sample one uncertain information source the GNSS orbits are known to be sensitive for. Thereby, uncertainty in the atmospheric state estimate is explicitly propagated to the ensemble of orbit solutions. The concept leads to interesting corollaries. Precise point positioning using the probabilistic orbit, for instance, becomes probabilistic, too.

How to cite: Järvinen, H., Navarro Trastoy, A., Tuppi, L., and Mayer-Gürr, T.: Probabilistic orbit solutions in GNSS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12696, https://doi.org/10.5194/egusphere-egu23-12696, 2023.

DORIS (Doppler Orbitography Radio positioning Integrated by Satellite) is a space-based piggyback satellite system that when used as a terrestrial measurement system can provide an accuracy of 10 cm in the absolute position measurement and in the order of sub-cm accuracy in relative measurements. When it rides piggyback on any satellite system can provide an orbital accuracy up to cm level. Precise Orbit Determination (POD) is the process of accurately tracking the position and velocity of a satellite in orbit. DORIS is an excellent satellite tracking system supporting the precise orbit determination of satellites. The accuracy of the POD does not affect only the quality of the estimated orbit ephemerides, but also the quantities derived from a free-network solution, mainly the station coordinates and the Earth rotation parameters (ERP). The precisely determined orbit can be used in many altimetric applications including estimating the mean sea surface, marine geoid, and vertical land motion, to derive vertical deflection and mean dynamic topography. Apart from that, the gravity field variations can also be determined more precisely.  GNSS data observations alone have been used so far in India to study the plate tectonics movements and earthquake predictions in the Indian subcontinent. Since DORIS and GNSS both have homogeneous network distributions and are complementary to each other, the DORIS data observations can be combined with GNSS data observations to study plate tectonics movements and earthquake predictions more effectively. Not only that since in DORIS the signal is transmitted from the ground, but processing DORIS measurement residue helps us to better understand and model what occurs in between the layers of the atmosphere which can be used for precise tropospheric modeling.

This space-based geodetic measurement technique has been used for the past three decades the world over, for precise measurement on the ground as well as on all oceanographic and altimetric satellite missions, it has not been introduced in India so far. Since our Space Research Organization has been launching several satellite missions and DORIS is being used for computation of the precise orbits, this technique has come to stay for a long time. The National Centre for Geodesy was set up by the Department of Science and Technology at the IIT Kanpur has also plans to set up a Geodesy village, where the DORIS station is going to be established and our DORIS data will be used in defining ITRF.

How to cite: Kumar, V., Dikshit, O., and Balasubramanian, N.: DORIS-based Precise Orbit Determination and its geodetic applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13557, https://doi.org/10.5194/egusphere-egu23-13557, 2023.

Numerous non-gravitational accelerations (NGAs) – due to radiation or gas-surface interactions – act on a typical satellite in low Earth orbit. The modeling of these accelerations is a key aspect of (reduced-)dynamic satellite precise orbit determination. Opposed to a purely empirical estimation of NGAs, especially orbit solutions with a high dynamical stiffness require an explicit NGA forward modelling. This is most important, e.g., for altimetry satellites which require utmost orbit accuracy especially in radial direction.

For explicit NGA modelling, a commonly employed strategy is to describe the satellite body in terms of a relatively simple macro model, i.e., a geometry composed of a number of elementary shapes like flat plates, spheres or cylinders, each of which with a specific size, orientation and surface property. During orbit integration, for each individual elementary surface NGAs are then computed based on analytical expressions and the sum over all surfaces yields the total NGA of the satellite at integration epoch. Often each of the elementary surface of the satellite macro model is treated fully independent from the other surfaces and interactions, in particular the (partial) occultation or shadowing of one surface by other surfaces is neglected. In case of satellites with significant non-convex shapes (like the altimetry satellite Sentinel-6A) this can lead to a marked degradation of NGA modeling. On the other hand, very detailed satellite geometry models together with techniques like ray tracing can provide highly accurate NGAs, however, at the price of significantly increased processing times.

In this contribution we assess the performance of a relatively simple self-shadowing algorithm for satellites described by a collection of flat convex polygons. Based on the relative plate locations, for each plate we analytically determine the amount of shadow cast by the other plates. We quantify the cost in terms of processing time and the impact on dynamic orbit solutions for the Copernicus Sentinel satellites in terms of empirical orbit parameters, observation residuals as well as other orbit quality metrics. We compare the so-derived NGAs and orbit solutions to results obtained with different other macro models and alternative approaches to take self-shadowing into account.

How to cite: Arnold, D., Peter, H., and Jäggi, A.: Simple self-shadowing in precise orbit determination of Copernicus Sentinel satellites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13569, https://doi.org/10.5194/egusphere-egu23-13569, 2023.

Ocean tides are small, periodic disturbances of the ocean state variables with frequencies related to the solar and lunar ephemerides. Most prominently, they are observed at the coasts by tide gauge measurements, where variations of the free sea surface height are visible even to the bare eye. On the other hand, tide gauges are just one geodetic technique that can identify ocean tide signatures. Especially satellite altimetry is considered the critical technology for constructing highly accurate data-constrained ocean tide atlases. However, the number of frequencies available from such atlases is limited by the signal-to-noise ratio of those observations, so not all tidal lines are readily available. To account for unresolved minor ocean tides, linear admittance approaches are utilized. On the other hand, unconstrained hydrodynamic ocean tide modeling with TiME (Sulzbach et al., 2021, 2022) allows us to calculate the oceanic response for any given tidal line explicitly.

Due to the long-wavelength character of ocean tidal loading, its geophysical fingerprint is not restricted to the oceans but extends horizontally (causing deformations of the crust to which instruments are attached) and vertically (causing periodic changes in gravity at orbital heights of in particular low-Earth orbiting satellites). Thus, tidal loading systematically disturbs both satellite orbits and also geodetic observations from ground stations with SLR, GNSS, and DORIS.

In this contribution, we compare tidal predictions from different ocean tide atlases. In addition to available Stokes coefficients of the gravity potential, we calculate vertical and horizontal displacements for 34 partial tide solutions from FES14, 17 from EOT20, and 57 from the data-unconstrained model TiME based on a spherical harmonic decomposition of maximum degree 4999. We focus on the influence of minor ocean tide solutions on the tidal predictions either drawn from the broadband TiME22-catalog or derived with the help of linear admittance from EOT20/FES14 major tides. The results are validated with time series of selected geodetic measurement systems to quantify the influence of the minor tide treatment on their residuals to motivate further efforts to reduce ocean tide residuals in precise orbit determination.

How to cite: Sulzbach, R., Balidakis, K., Öhlinger, F., Mayer-Gürr, T., Dobslaw, H., and Thomas, M.: Impact of Minor Ocean Tides on Surface Deformations and the Earth’s Gravity Field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15862, https://doi.org/10.5194/egusphere-egu23-15862, 2023.

CubeSats constellations using commercial off-the-shelf components have been studied for different applications, such as GNSS Radio Occultation (GNSS-RO). Furthermore, precise orbit determination of Low Earth Orbit (LEO) CubeSats based on multiple GNSS constellations would open new opportunities for scientific applications such as Earth’s gravity field measurements.

In GNSS kinematic orbit determination, which is the common method used for small sats, the derived orbits are affected by noise, data gaps, outliers, measurement errors as well as poor geometry of the observations. Our work seeks to mitigate these issues and we present two areas of research: 1) GNSS network processing of GPS and Galileo constellations and 2) kinematic orbit determination of a set of Spire CubeSats that host a GNSS-RO payload. An initial architecture of kinematic orbit processing for the Spire GNSS-RO CubeSats constellation is obtained and the details on validations and limitations are discussed in more details. In addition, we showcase the agreement between the GNSS orbit products produced at the University of Luxembourg (UL) with those of the Center for Orbit Determination in Europe (CODE). Finally, the Spire kinematic orbits based on the raw observation approach are derived and compared to the L1B Spire orbit products.

How to cite: Shafiei, P., Bemtgen, J., Talpe, M., and Tabibi, S.: Initial Orbit Determination Results from the University of Luxembourg using Spire GNSS Tracking Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15932, https://doi.org/10.5194/egusphere-egu23-15932, 2023.

The Copernicus Precise Orbit Determination (CPOD) Service generates routinely precise orbital products of Sentinel-1, -2, -3 and -6 for its operational use by ESA and EUMETSAT. The accuracy of these products depends on the quality of the inputs used, particularly the gravity field and the GNSS orbits and clocks. This abstract focusses on the impact of the gravity field using the COST-G geopotential models.

Currently, the CPOD Service is using the EIGEN-GRGS-RL04 mean gravity field model, which dates back in 2019. In the framework of COST-G (Combination Service for Time-variable Gravity Fields) a new series of gravity fields is being generated quarterly by AIUB (Astronomical Institute, University of Bern), as a fit to a weighted combination of monthly gravity fields generated by different analysis centres. The monthly gravity fields models are generated based on GRACE-FO data, so they are capable of accurately catching up the recent changes in the gravity field. These models improve the operational orbit results significantly. Since these fitted signal models (FSM) only cover the GRACE-FO period they are not suitable for consistent reprocessing of entire mission times beyond 2018. In order to support such reprocessing activities an additional COST-G FSM has been generated covering the GRACE and GRACE-FO period. 

The use of the COST-G products has been proposed to substitute the current EIGEN-GRGS-RL04 mean gravity field model within the Copernicus Precise Orbit Determination (CPOD) Service. Based on limited reprocessing campaigns (from 2019 onwards) of Sentinel-3 A&B using both geopotentials (EIGEN and COST-G), it has shown that the COST-G FSMs represent improvements on the orbital accuracy and yields smaller dispersion of empirical accelerations.

Thanks to the recent availability of a new full COST-G FSM covering the GRACE and GRACE-FO period, the present work will extend this analysis to the Sentinel-1, -2 and -6 missions as well, including the full mission (e.g., from 2014 in the case of Sentinel-1A), to confirm the potential benefits of COST-G FSMs.

It is worth mentioning that this analysis will be performed with FocusPOD, a new GMV state-of-the-art POD SW.

How to cite: Berzosa, J., Fernández Martín, C., Matuszak, M., Fernández Usón, M., Fernández Sánchez, J., Nogueira Lodd, C., Femenias, P., Peter, H., and Meyer, U.: Reprocessing of Copernicus Sentinel POD solutions with COST-G geopotential models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16137, https://doi.org/10.5194/egusphere-egu23-16137, 2023.

JPL's newly developed software for determining terrestrial reference frames, known as SREF (Square-root Reference frame Estimation Filter), has been used to produce JTRF2020, a combined terrestrial reference frame determined from the input SINEX files submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. SREF, being based on a square-root information filter and smoother, determines the reference frame sequentially from the input station position time series. For JTRF2020, 525 GNSS, 194 DORIS, 116 SLR, and 96 VLBI, or a total of 931, station position time series were used. Incorporating process noise in SREF, determined from geophysical fluid loading models, allows the observed station positions to be smoothed between discontinuities caused by earthquakes and equipment changes. Reference frames determined by SREF, like JTRF2020, are represented by this set of smoothed station position time series. SREF also fits a model to the station's observations and uses the model to fill gaps in the station's observing history, to forecast the position of the station after it stopped observing, and to hindcast its position before it started observing. For JTRF2020, the model consists of a piecewise linear trend, an annual periodic term, and a sum of exponential terms to represent postseismic motion for those stations that experience postseismic motion. The result of using SREF to determine JTRF2020 will be presented.

How to cite: Gross, R., Abbondanza, C., Chin, M., Heflin, M., and Parker, J.: JTRF2020: Results and Next Steps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2117, https://doi.org/10.5194/egusphere-egu23-2117, 2023.

JTRF2020 is the latest TRF solution computed at JPL by assimilating frame input data submitted by the IVS, IGS, ILRS, and IDS for ITRF2020. Determined with SREF (Square-root Reference frame Estimation Filter), a computational code based on a square-root information filter and Dyer-McReynolds smoother algorithm, JTRF2020 adopts a time-series based representation: Its daily time series determined from observations of a multi-technique space-geodetic network of 931 stations describe, through their Cartesian coordinates, the deformation of solid Earth as a function of time. Such coordinates are inherently expressed in Earth’s Center of Mass as sensed by SLR and give access to the quasi-instantaneous scale implied by the underlying frame.  JTRF2020, like its predecessor JTRF2014, traditionally adopts a scale relying on VLBI and SLR observations only. In this presentation, we will guide the readers through the process we adopted to define and construct the scale of JTRF2020, from the determination and analysis of the scale differences between VLBI and SLR to the way in which the time-variable scale bias between VLBI and SLR is handled within the J2020 assimilation.     

How to cite: Abbondanza, C., Chin, T., Gross, R., Heflin, M., and Parker, J.: An Insight on Scale Definition in JTRF2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3212, https://doi.org/10.5194/egusphere-egu23-3212, 2023.

Today, Global Navigation Satellite Systems (GNSS) are widely used to study the kinematics of the Earth's surface and provide a fundamental contribution to the establishment of terrestrial reference frames. GNSS station position time series are derived by different analysis centres, which have achieved tremendous progress over the years. Nevertheless, GNSS station position time series remain polluted by stochastic variations – often called "noise" – which hinder their geophysical interpretation and contribution to terrestrial reference frames.

Many studies have evidenced that these stochastic variations exhibit both temporal and spatial correlations. On the one hand, temporal correlations have been analyzed in detail and are known to be well approximated by a combination of white noise and flicker noise. The presence of flicker noise, whose origin remains unknown, is a major source of uncertainty in the estimation of long-term station positions and velocities. Consequently, most geodetic studies now routinely take these temporal correlations into account to avoid inferring unrealistically optimistic uncertainties. On the other hand, the stochastic variations in GNSS station position time series are also spatially correlated up to distances reaching a few thousand kilometres. The origins of these large-scale correlations, whether non or poorly-modelled ground deformation, positioning errors, or a combination of both, remain to be understood. Although this spatially correlated noise is known to obscure geophysical signals and affect the estimation of parameters of interest, it is hardly ever modelled or accounted for.

This presentation introduces a realistic spatio-temporal correlation model for the stochastic variations in GNSS station position time series. Based on the analysis of position time series from the IGS repro3 campaign (over 1,300 stations) and the Nevada Geodetic Laboratory analyzes (over 11,000 stations), we first provide a diagnosis of the spatial correlations of the white and flicker noise processes separately. We then introduce three-dimensional spatial correlation models for each process. Finally, we discuss the implications of these spatio-temporal correlations on the uncertainty of long-term station positions and velocities.

How to cite: Gobron, K., Rebischung, P., Barnéoud, J., Chanard, K., and Altamimi, Z.: Toward a realistic spatio-temporal description of GNSS station position time series, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3399, https://doi.org/10.5194/egusphere-egu23-3399, 2023.

In the context of the 2020 realization of the International Terrestrial Reference Frame, the three IERS Production Centers (DGFI, IGN and JPL) delivered three independent solutions from the contributions of the four space geodetic techniques (DORIS, GNSS, SLR and VLBI). Even if these three ITRF2020 realizations are based on the same input, they differ on several points such as the space geodetic techniques weighting, the coordinate time series discontinuities and on the modelling of the station displacements.

In this study, we use the coordinate time series of the two hundred DORIS stations from 1993.0 to 2022.5 as benchmark to investigate the characteristics of the ITRF2020 and DTRF2020 realizations.

After presentation of the overall performance of these two TRF realizations in terms of geocenter, scale and mean velocities, we assess the quality of the weekly restitution of the DORIS station positions by the DTRF2020, and ITRF2020 solutions. Then, we make benefit of the one and a half year since the ending of the ITRF2020 time period to evaluate these two 2020 TRF solutions in terms of prediction of the DORIS station positions. Finally, we will estimate the impact of the DTRF2020 and ITRF2020 solutions on DORIS precise orbit determination.

How to cite: Moreaux, G. and Capdeville, H.: IDS evaluation of the DORIS versions of the DGFI and IGN TRF2020 solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3452, https://doi.org/10.5194/egusphere-egu23-3452, 2023.

For various geodetic and geophysical applications, users need to have access to a Plate Motion Model (PMM) that is consistent with the ITRF2020 frame. The aim of this paper is to evaluate different possible approaches for determining a PMM from the horizontal velocities of a subset of the ITRF2020 sites away from plate boundaries, Glacial Isostatic Adjustment regions and other deformation zones. Compared with the ITRF2014-PMM, we assess in particular the performance of a PMM based on ITRF2020 velocity field, which contains more sites in some large tectonic plates, such as North and South Americas, Australia, and to some extent Antarctica. Using a global inversion of all plates all together, with full variance-covariance information, the angular velocities of these plates are expected to be improved in the ITRF2020 plate motion model. We also investigate the impact of subtracting GIA horizontal velocity predictions of different models before adjusting for angular plate velocities. Early results will be presented and discussed.

How to cite: Altamimi, Z., Métivier, L., Rebischung, P., Collilieux, X., and Chanard, K.: Towards an ITRF2020 plate motion model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3962, https://doi.org/10.5194/egusphere-egu23-3962, 2023.

Satellite laser ranging (SLR) is currently one of the four space geodetic techniques that provide a relevant contribution to the International Terrestrial Reference Frame (ITRF) realization as well as to the determination of global geodetic parameters including the low-degree harmonics of the Earth's gravity potential. ITRF realizations are mostly based on the observations to the two LAGEOS and two Etalon satellites, however, the impact of observations to Etalon satellites is marginal when compared to LAGEOS. Currently under consideration is an extension of the ITRF solution to include the LAser RElativity Satellite (LARES) and LARES-2 developed by the Italian Space Agency ASI and launched on July 13, 2022. The contribution of other satellites with retroreflectors is still being investigated.

This study aims to verify various approaches to estimating geodetic parameters depending on the number of determined empirical once-per-revolution parameters for satellite orbits and different approaches of parametrization for the Earth rotation parameters (ERP), including piecewise linear and piecewise constant parametrization. We analyze six parametrizations, where three of them are proposed in this study and the other three are used by research centers, such as the Center for Space Research (CSR), the International GNSS Service (IGS), and the International Laser Ranging System (ILRS). For IGS and ILRS, these are the approaches used in determining the ERPs based on GNSS and SLR data, respectively. To the constellation of geodetic satellites such as LAGEOS-1/-2, Etalon-1/-2, and LARES-1/-2, we add hypothetical SLR satellites such as LARES-3/-4 and LARES-5/-6 which supplement the current constellation in the simulation study. We check whether satellite parameters, such as satellite altitudes and inclination angles affect individual global geodetic parameters when using different approaches to ERP parameterization and the set of estimated empirical orbit parameters.

The obtained results show that the value of the obtained formal errors may depend not only on the choice of the estimated geodetic parameters but also on the number of satellites or satellite orbit parameters involved in the calculations.

How to cite: Najder, J., Sośnica, K., Strugarek, D., and Zajdel, R.: Different approaches in determining global geodetic parameters from SLR data - a simulation study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6235, https://doi.org/10.5194/egusphere-egu23-6235, 2023.

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) envisages stringent goals for the International Terrestrial Reference Frame (ITRF) realization in terms of accuracy (1 mm) and precision (0.1 mm/year). These requirements entail that the Earth Orientation Parameters (EOP) should be estimated with similar accuracy.

The conventional International Terrestrial Reference Frame (ITRF) is based on the combination of solutions from four space geodetic techniques, including observations until the end of 2020, incorporating updated data and models. On the other hand, the Celestial Reference Frame (CRF) is a VLBI-only solution based on data until 2015, provided by one sole VLBI-analysis centre. Additionally, the current conventional EOP series, IERS 14 C04, is also produced in a separate process following a different analysis and combination strategy. It is based on a combination of monthly EOP estimates obtained by the combination centres of each space geodetic technique. These disparate approaches might cause a slow degradation of the consistency among EOP and the reference frames or a misalignment of the current conventional EOP series. The recent release of the ITRF2020 brings an exciting opportunity to investigate this topic.

In this work, we empirically assess the consistency among the conventional terrestrial reference frame (TRF) and celestial reference frame (CRF), and EOP through the analysis of Very Long Baseline Interferometry (VLBI) historical data, taking different TRFs as alternative settings in the analysis: ITRF2020, VTRF2020, ITRF2014, and the terrestrial frame consistent with the newest Celestial Reference Frame (i.e., ICRF3). Additionally, Helmert transformations are computed to evaluate to which extent the behaviour that may be found in the previous point can be attributed to orientation differences of the TRFs themselves. Finally, different CRF realizations (ICRF2 and ICRF3) are tested to study their impact on the EOP, especially in the long term, paying attention to the appearance of biases and trends among the EOP series.

This study allows evaluation if the selection of the TRFs and/or the CRFs has a significant impact on the consistency of the estimated EOP and assesses its agreement with the conventional EOP series.

How to cite: Moreira, M., Azcue, E., Karbon, M., Belda, S., Puente, V., Heinkelmann, R., Gordon, D., and Ferrándiz, J.: VLBI-based assessment of the consistency of the conventional EOP series and the reference frames (terrestrial and celestial), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8636, https://doi.org/10.5194/egusphere-egu23-8636, 2023.

Each space geodetic technique realizes its own technique-specific terrestrial frame. Combining the individual techniques requires the links between those frames such as the local tie vectors. Co-location of different geodetic techniques on Earth orbiting satellites offers the unique opportunity of continuously measure ‘space-ties’ which can have a critical role for achieving the Global Geodetic Observing System (GGOS) goal of 1mm accuracy and 0.1mm/year stability of the Terrestrial Reference Frame (ITRF).

We simulate Very Long Baseline Interferometry (VLBI) observations of a broadband VLBI transmitter (VT) onboard Galileo satellites to evaluate the contribution of such a VT space-tie on the rotation transformation between the VLBI and GNSS frames. We investigate the contribution of a VT as space tie by evaluating the formal precision of orientation parameters between the VLBI and GNSS frames using different ground stations/baselines to find the observation geometry for the rotation transformation.

How to cite: Sert, H., Hugentobler, U., Karatekin, O., and Dehant, V.: Optimal geometry for reference frame rotation transformation using VLBI-GNSS space-tie onboard Galileo satellites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8773, https://doi.org/10.5194/egusphere-egu23-8773, 2023.

Space geodesy is the branch of science that deals with determining the shape and dimension of the Earth using quasars and artificial satellites. However, the use of space techniques is not limited to geodesy, many recent geodynamical interpretations are based on the velocities determined using GNSS (Global Navigations Satellite System). In this regard, reference frame differences as well as processing strategies - Precise Point Positioning (PPP) or Network Solution (NS) - may induce systematic differences of significant values. A first comparison between NGL (Nevada Geodetic Laboratory) PPP-produced and IGS (International GNSS Service) NS-produced (repro3) products showed systematic differences between both sets of displacement time series. While the discrepancies in the noise parameters are quite understandable and interpretable, the systematic disagreements in the velocities or amplitudes of annual signals are concerning. The repro3 daily combined solutions are aligned in origin and orientation to the IGSR3 reference frame, which inherits its origin and orientation from ITRF2014. So the daily repro3 station positions are expressed with respect to the ITRF2014 origin, which follows CM on the long-term, but reflects CF at sub-secular time scales. NGL time series, just like the IGS ones, are aligned to a linear reference frame, IGS14 in their case. Since both the IGS repro3 and NGL time series are in fact with respect to the ITRF2014 origin, this cannot explain the annual amplitude differences we observe. A difference in scale may contribute though, because the NGL time series are aligned in scale to IGS14, but the repro3 time series are not aligned in scale to any reference frame. They inherit their scale from the radial satellite phase center offsets (z-PCOs) in igsR3.atx, so in general we may expect: (1) an average ~8 mm difference between the vertical positions in both sets of time series at epoch 2010.0, (2) an average ~0.2 mm/yr rate between the vertical positions in both sets of time series, (3) small differences in the vertical seasonal signals due to the network effect occurring when the NGL solutions are aligned in scale to IGS14. But the fact that the NGL solutions are aligned in scale to the reference frame, while the IGS solutions are not, might explain some other systematic differences. To verify that, we compared the aforementioned series to a set of special IGS repro3 time series produced at IGN and aligned not only in origin and orientation, but also in scale to the IGSR3 reference frame. The comparison between the series was made at 607 stations distributed around the world. The Up component was investigated, and the data have been cut to the same ranges in all three solutions (namely, IGS, NGL and IGN) to avoid misinterpretations and have a minimum length of 5 years. Velocities as well as amplitudes of annual and draconitic oscillations have been analyzed revealing very interesting spatial patterns in the differences.

How to cite: Bogusz, J., Rebischung, P., and Klos, A.: On the systematic differences between various GNSS solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8947, https://doi.org/10.5194/egusphere-egu23-8947, 2023.

Improving and homogenizing time and space reference systems on Earth and, more specifically, realizing the Terrestrial Reference Frame (TRF) with an accuracy of 1 mm and a long-term stability of 0.1 mm/year are crucial  to many scientific and societal endeavors. This is the purpose of the GENESIS mission, proposed as a component of the FutureNAV program of the European Space Agency (ESA) [1].  The knowledge of the TRF is fundamental for Earth and navigation sciences. For instance, quantifying sea level change strongly depends on an accurate determination of the geocenter motion but also of the positions of continental and island reference stations, such as those located at tide gauges, as well as the ground stations of tracking networks. In addition, numerous applications in geophysics require absolute millimeter precision from the reference frame, as, for example, monitoring tectonic motion or crustal deformation, contributing to a better understanding of natural hazards. The target TRF accuracy  is based on the scientific needs of various disciplines in Earth Sciences and is reflected in the consensus of various authorities, including the International Association of Geodesy (IAG). Moreover, the United Nations Resolution 69/266 states that the full societal benefits in developing satellite missions for positioning and Remote Sensing of the Earth are realized only if they are referenced to a common global geodetic reference frame at the national, regional and global levels. Yet, when combining all these techniques for the TRF generation, the process is today affected by the accuracy on which we may determine the differential coordinates between the reference point of each technique and several unmodelled systematic errors. 

The GENESIS platform will be a dynamic space geodetic observatory carrying all the geodetic instruments referenced to one another through carefully calibrated space ties. GENESIS will support the production of a more accurate TRF and enable the generation of an updated global model of Earth rotation, as well as a better-determined geocenter. The GENESIS mission would deliver exemplary science and societal benefits across a multidisciplinary range of Navigation and Earth sciences applications, constituting a global infrastructure that is internationally agreed to be strongly desirable. GENESIS got the green light at the  ESA Ministerials  held in Paris on November 2022. Here we will present the latest updates on the overall mission.

[1] Delva et al., 2023, GENESIS: co‐location of geodetic techniques in space, accepted in Earth, Planets and Space

How to cite: Karatekin, Ö. and the GENESIS Team: ESA’s GENESIS mission: Advancing terrestrial reference systems by co-location of geodetic techniques in space., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9320, https://doi.org/10.5194/egusphere-egu23-9320, 2023.

Geodetic network infrastructure has evolved with increasing pace the past decade with remarkable additions of modern hardware, replacing aging, ‘80s vintage equipment throughout the globe. SLR needs however more than updating the network to deliver the accuracy required today. New and improved design “targets” must also be used that support the required “1-mm accuracy”. LAGEOS was conceived and built in the early ‘70s with a ~5 mm accuracy in mind [Pearlman et al., 2019]. This limitation forced analysts to develop approaches of data analysis to ensure that even with such data one can reach the required 1-mm accuracy [Luceri et al., 2019]. Along with the network updates a parallel effort was thus initiated to modernize the space segment as well. Initially with the design and launch of LARES in 2012 [Pavlis et al., 2015] and following that, the design of LARES-2 [Ciufolini et al., 2017, Paolozzi et al., 2019], which was successfully launched on July 13, 2022 [https://www.nature.com/articles/d41586-022-02034-x]. The new mm-accurate target was quickly acquired first by the Italian station at Matera, only three days after launch and although very early in the mission, the data were of remarkably high quality and insignificant bias. This prompted a quick evaluation and a test inclusion of this target in the limited list of SLR targets supporting the ITRF development. With an orbit nearly identical to LAGEOS (with supplementary inclination), taking full advantage of all the appropriate models designed and applied to LAGEOS, we achieved 7-day orbital fits of 3-5 mm even without a tuned target signature correction. Using the approach described in [Kuzmicz-Cieslak, M. et al., 2022] and along with data from the other geodetic spheres, we have generated preliminary combination products for the development of the ITRF. We will present an overview of this initial analysis of LARES-2 data focusing on comparing these results to contemporaneously taken data from the standard four geodetic spheres only, (LAGEOS 1 & 2 and Etalon 1 & 2).

Pearlman et al. J Geod 93, 2181–2194 (2019). https://doi.org/10.1007/s00190-019-01228-y

Luceri et al. J Geod 93, 2357–2366 (2019). https://doi.org/10.1007/s00190-019-01319-w

Pavlis et al. EEEIC (2015), pp. 1989-1994. https://doi.org/10.1109/EEEIC.2015.7165479

Paolozzi et al. J Geod 93, 2437–2446 (2019). https://doi.org/10.1007/s00190-019-01316-z

Ciufolini et al. Eur. Phys. J. Plus 132, 336 (2017). https://doi.org/10.1140/epjp/i2017-11635-1

Kuzmicz-Cieslak, M. et al. (2022). https://doi.org/10.22541/essoar.167214343.32185093/v1

How to cite: Pavlis, E. C., Kuzmicz-Cieslak, M., and Evans, K.: Incorporating LARES-2 SLR Data in ILRS Products for ITRF Development, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9417, https://doi.org/10.5194/egusphere-egu23-9417, 2023.

JTRF2020 is a recent contribution by NASA Jet Propulsion Laboratory to IERS as part of their effort to determine ITRF2020.  JTRF2020 is estimated daily using a sequential computational method (called "SREF") based on the SRIF and DMCS algorithms which are respective variants of the Kalman filter and smoother.  The filtering algorithm allows us to make timely update of the reference frame, as newer geodetic analysis data become available beyond those ingested into JTRF2020.  Benefits of such frame updating are examined using hindcasting experiments, which are presented here.  Also, some of the standard formulas used in terrestrial reference frame realizations are not immediately suitable for sequential formulation required by the algorithms like the Kalman filter.  We thus describe our sequential re-formulation of these formulas, including the intrinsic constraints, week-long EOP arcs, and lack of initial conditions.

How to cite: Chin, T. M., Abbondanza, C., Gross, R., Heflin, M., and Parker, J.: Updating Terrestrial Reference Frame using Sequential Computation Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9468, https://doi.org/10.5194/egusphere-egu23-9468, 2023.

Reducing uncertainties in long-term GNSS is crucial for providing the most stable realization of terrestrial reference frames. Besides the epoch-wise handling of errors in the GNSS processing of the raw observations, this includes the description of linear and non-linear station motions by using functional and stochastic time series models (trajectory models). While the state-of-the-art trajectory models explain common signals (such as station velocity, periodic motions and offsets), a main challenge is to explain the variety of signals that are still present in the residuals (i.e., transients and artifacts).

We take the time series of almost 2000 stations from Europe and the Western U.S., and fit extended trajectory models (ETMs) using the Hector software. We show that correcting the vertical observations by geophysical loadings and common-mode errors (CME) enhances median GNSS sensitivity by a factor of two, which we demonstrate for important parameters of the ETM, for both, linear and non-linear motions. The analysis reveals a median sensitivity of 0.5 mm/year for station velocity, and 0.6 mm for annual seasonal motions. Supported by the comparison with the CME-corrected case, we highlight potential shortcomings of the non-tidal atmospheric and hydrological loading models (related to phase shifts and the presence of transients), and demonstrate biasing effects on uncertainty.

Based on the post-fit residuals of the ETMs and unsupervised learning methods, yet unexplained geophysical transients can be classified and clustered, which is a significant step towards automatic data interpretation and quality control. In view of an optimal GNSS station deployment, this approach also helps to separate stable from unstable regions, for example regions of irregular subsidence.  We conclude, that this algorithmic framework cannot only be successfully used for GNSS data, but also for other geodetic time series data.

How to cite: Hohensinn, R. and Bock, Y.: From noise-to-signal: enhancing the sensitivity of long-term GNSS by explaining non-linear station motions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10251, https://doi.org/10.5194/egusphere-egu23-10251, 2023.

The IVS Combination Centre, operated by the Federal Agency for Cartography and Geodesy (BKG, Germany) in close cooperation with the Deutsches Geodätisches Forschungsinstitut (DGFI-TUM, Germany), generates and releases the combined products of the International VLBI Service for Geodesy and Astrometry (IVS). These session-wise solutions are achieved by an intra-technique combination utilizing the individual contributions delivered by multiple IVS Analysis Centres (AC). For the IVS contribution to the ITRF2020, the re-processed sessions containing 24 h VLBI observations have been submitted by eleven different ACs, where a total number of seven different software packages are utilized. As a result, the session-wise SINEX files are delivered, including datum-free normal equations containing the station coordinates, the source positions and full sets of the Earth Orientation Parameters (EOP). As the same software packages are used by various ACs (e.g. CalcSolve by five ACs), the combined solution is in danger of being dominated by these contributions. The estimates of EOP and station coordinates are affected then mainly by the software specific modelling.

This work focuses on an optimal weighting strategy to handle dependencies due to identical software packages in the ACs’ contributions. Thereby, software specific sub-combinations are carried out in the first step to employ the strategy. Finally, the ultimate combination consists of the weighted individual contributions of each applied software. In order to assess the quality of the individual components of the combination - especially in comparison to the contributions of the individual ACs – the internal as well as the external comparisons of the estimated EOP are carried out, where the combined solution together with the external time series (e.g., IERS Bulletin A) serve as a reference.

How to cite: Hellmers, H., Modiri, S., Thaller, D., Bloßfeld, M., and Seitz, M.: Intra-technique VLBI combination by handling software-specific dependencies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11531, https://doi.org/10.5194/egusphere-egu23-11531, 2023.

In 2022-2023, new (2020) realizations of the International Terrestrial Reference System (ITRS) were published, namely ITRF2020, DTRF2020, and JTRF2020. One of the differences for these realizations with respect to the previous (2014) ones is the application of Satellite Laser Ranging (SLR) station-specific long-term mean range biases for the four geodetic satellites LAGEOS-1, -2 and Etalon-1 and -2. These range biases were subtracted at the observation level from the SLR observations used to derive the ITRS2020 realizations. In this context, a question arises if these range biases should be applied in SLR-observation-based precise orbit determination for any satellite to obtain the highest orbit quality possible, when using ITRS2020 realizations as the a priori reference frame. We present results of a study on the application of the SLR long-term mean range biases derived from LAGEOS-1, -2 and Etalon-1 and -2 for precise orbit determination of some altimetry and other spherical SLR satellites using ITRS2020 realizations as the a priori reference frame and make a conclusion on the necessity of application of these biases. Furthermore, we present results of precise orbit determination for altimetry satellites based on long-term mean range biases explicitly determined for the respective satellites.

How to cite: Rudenko, S., Bloßfeld, M., Zeitlhöfler, J., Kehm, A., and Dettmering, D.: Impact of SLR long-term mean range biases on the orbits of altimetry and SLR satellites for ITRS2020 realizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11703, https://doi.org/10.5194/egusphere-egu23-11703, 2023.

The DTRF2020 is the ITRS 2020 realization of the ITRS CC at DGFI-TUM.It was published earlier this year. The calculation of the DTRF2020 is based on a two-step approach: First, after a data pre-analysis, one TRF (normal equation system, NEQ) per technique, i.e. VLBI, SLR, GNSS and DORIS, is calculated. Second, the TRF NEQs are combined to the DTRF2020 solution. For the first time, all previously modeled non-tidal loading (NTL) components provided by IERS GGFC, i.e., the atmospheric, hydrological, and oceanic parts, are considered to reduce NTL signals in the station motions from the input NEQ. Post-seismic deformation (PSD) signals in station position time series are approximated by combinations of logarithmic and exponential functions and reduced from the NEQ in the same way as the NTL signals in the first step of our approach.

The published dataset includes the DTRF2020 solution itself, i.e., station positions at the reference epoch 2010.0 and station velocities, as well as the consistently estimated EOP series. In addition, the model-based NTL time series used in the DTRF2020 calculation, the parameters of the PSD approximation functions, and the corresponding time series of the approximation signal considered in DTRF2020 (over the DTRF2020 time period) are provided for the users. Furthermore, residual time series of station positions and SLR translation time series are made available (the latter indicate the deviation of the instantaneous from the mean center of mass realized in DTRF2020).

In this presentation, we discuss the final results of DTRF2020 and give an overview of the DTRF2020 dataset and the features it provides for its application. We also discuss the consistency of DTRF2020 with respect to its predecessor DTRF2014 and the limits of accuracy of reference frames. Further, we address the need for consistency with respect to datasets that will be used in DTRF2020 applications, such as the SLR Data Handling File and GNSS satellite PCV.

How to cite: Seitz, M., Blossfeld, M., Glomsda, M., Angermann, D., Rudenko, S., Zeitlhoefler, J., and Seitz, F.: DTRF2020: Strategy, Results and Data Set, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12029, https://doi.org/10.5194/egusphere-egu23-12029, 2023.

The ITRS CC at the Deutsches Geodätisches Forschungsinstitut of the Technical University of Munich (DGFI-TUM) has created the new DTRF website https://dtrf.dgfi.tum.de. On this site, DGFI-TUM provides background information and data access to the current and all previous DTRF solutions. In particular, the DTRF2020 processing strategy is presented and the results are described and explained. In addition to the actual solution, the DTRF2020 release contains further datasets that are necessary for a highly accurate application of the DTRF2020. The website clearly presents and makes available all datasets, partly map-based. Our poster gives an overview of the new DTRF website and provides examples of its use.

How to cite: Seitz, F., Seitz, M., Bloßfeld, M., Glomsda, M., Angermann, D., Rudenko, S., and Zeitlhöfler, J.: New website of the ITRS CC at DGFI-TUM: dtrf.dgfi.tum.de, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12089, https://doi.org/10.5194/egusphere-egu23-12089, 2023.

With the integration of positioning solutions into mass-production autonomous driving systems, together with the ever-increasing demand for global positioning applications the use of a global reference frame is now a requirement that global correction service providers need to support and deliver, whilst still maintaining support of local (regional) official reference frames. To maintain high precision of the GNSS network we perform a daily solution, which is computed based on precise orbits and following the guidelines of the EPN Analysis Centres. Using the daily solutions, we are estimating the linear velocity of reference stations within GNSS networks and are also considering jumps due to equipment changes. The estimated velocities give the opportunity to monitor the long-term stability of the network as well as the quality of reference station coordinates. The transition between ITRF2014 and ITRF2020 on a large GNSS reference stations worldwide, including the computation of the HxGN SmartNet GNSS network consisting of more than 5300 GNSS reference stations, will be investigated to evaluate the impact that this could have on the users using the correction services.

The daily solution and monitoring of GNSS networks, such as HxGN SmartNet, is executed by the Leica Geosystems solution named Leica CrossCheck, which is based on Bernese GNSS software. Leica CrossCheck is capable to monitor GNSS networks of all scales.

KEYWORDS: GNSS reference station network, Bernese GNSS 5.4, Leica CrossCheck, Leica GNSS Spider, HxGN SmartNet, Leica GeoMoS Now!

References:
Dach, R., S. Lutz, P. Walser, P. Fridez (Eds); 2015: Bernese GNSS Software Version 5.2. User manual, Astronomical Institute, Universtiy of Bern, Bern Open Publishing. DOI: 10.7892/boris.72297; ISBN: 978-3-906813-05-9.

How to cite: Matonti, F., Miller, A., and Wnuk, J.: The introduction of ITRF2020 in global positioning applications, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12442, https://doi.org/10.5194/egusphere-egu23-12442, 2023.

In the multi-technique integrated solution, different space geodetic techniques are combined via common parameters and external observations, such as global ties (Earth Orientation Parameters, EOPs) and local ties (LTs), respectively. Local ties, which directly link the coordinates of co-location stations, are currently used in determining terrestrial reference frames (TRFs). We investigate the impact of global and local ties in Global Navigation Satellite Systems (GNSSs) and Very Long Baseline Interferometry (VLBI) integrated solutions in five VLBI continuous (CONT) campaigns. Compared to a baseline solution where GNSS and VLBI have separate minimal constraints implemented (no-net-rotation and no-net-translation, NNR+NNT), applying additional GTs and LTs improves the VLBI TRF and EOP estimates. As LTs are supposed to transfer the datum information between GNSS and VLBI, we further investigate the scenario where the VLBI datum is linked to GNSS via LT, without NNR+NNT applied to the VLBI network. We demonstrate that in this scenario the VLBI solution is deteriorated, especially the east-west component of station coordinates and UT1-UTC estimates, mainly due to the insufficient accuracy of the currently used LTs. We thus emphasize the importance of improving the accuracy of LT measurements and applying additional ties, for example, space ties and atmospheric ties.

How to cite: Wang, J., Glaser, S., Ge, M., Balidakis, K., Heinkelmann, R., and Schuh, H.: Impact of Local Ties in GNSS and VLBI Integrated Solution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12556, https://doi.org/10.5194/egusphere-egu23-12556, 2023.

The influence of ocean tides plays a major role for geodetic space methods in the modeling of satellite orbits, Earth rotation, and short-period station motions.

Current ocean tide models are published with a large number of individual constituents that are representative for the entire tidal spectrum. The analysis requires interpolation of the constituents onto the spectrum using admittance theory. The application of admittance is non-trivial, as it explicitly and implicitly refers to historical conventions that are hard to retrace for users. Further linear admittance theory is non-unique and requires some insight into the principles of ocean tidal dynamics.

Nonetheless, the error-prone implementation of admittance is mostly left to the user, which can easily induce confusion and errors. For example, the IERS2010 conventions describe only one method for the outdated FES2004 model that does not apply directly to current models. While there is a conventional routine for calculating the ocean loading displacement, it needs to consider recent developments and therefore does not exploit the full potential of current ocean tide models.

In this presentation, a unified approach is presented for discussion to exploit the full potential of current ocean tide models in satellite orbit calculation and for station displacements. This approach aims to set up a framework for tidal correction that is userfriendly, model-independent, and applies to many geophysical observables.

How to cite: Mayer-Guerr, T., Oehlinger, F., Sulzbach, R., and Dobslaw, H.: Exploiting the full potential of ocean tide models for space geodetic techniques, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13235, https://doi.org/10.5194/egusphere-egu23-13235, 2023.

The realization of a terrestrial and celestial reference frame is a fundamental requirement for all ground- and space-based observations, making the interpretation of key global processes on Earth possible and therefore contributing to a better understanding of the Earth system. In this matter, the space-geodetic technique called Very Long Baseline Interferometry (VLBI) provides the perfect link between stations on the Earth's surface and extragalactic sources with a quasi-fixed position. In the process of an intra-technique combination, it is possible to estimate parameters that are common to all VLBI sessions in a common least squares adjustment, resulting in, e.g., catalogs of station and source positions (and station velocities) at a certain reference epoch. 

We present the current status of our new state-of-the-art and stand-alone Python software for the combination of VLBI sessions developed at the VLBI Analysis Center in Vienna. The combination process is based on homogenized, datum-free normal equations from SINEX (solution independent exchange format) files. In the future, we are planning on implementing filter solutions to ensure an optimal state estimation of the dynamical system Earth and further expanding the capabilities of our software by, e.g., allowing a combined analysis of different space-geodetic techniques (inter-technique combination) to further improve the consistency and accuracy of the resulting reference frames and Earth Rotation Parameters (ERPs). 

How to cite: Kern, L., Krasna, H., Böhm, J., and Madzak, M.: Current status and future perspectives of VLBI global solutions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13970, https://doi.org/10.5194/egusphere-egu23-13970, 2023.

The German Research Centre for Geosciences (GFZ) is one of the Associate Analysis Centers (AAC) of the International Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) Service (IDS).

In the framework of a future contribution to the DORIS part of the International Terrestrial Reference Frame (ITRF) a repertoire of well-known satellite altimetry missions equipped with DORIS receiver, in particular Topex, Envisat, Jason-1/2, Cryosat-2, Saral, Jason-3, Sentinel-3A/B and Sentinel-6A Michael Freilich, have been processed.

Therefore, Precise Orbit Determination (POD) is performed for these missions, and orbits are generated based on DORIS-only and on the combination of DORIS and Satellite Laser Raging (SLR) observations.

The quality of the orbits is subsequentely analyzed internally and in comparison with external orbit solutions.

For external comparisons, the combined orbit solutions of the Copernicus POD quality working group (CPOD-QWG), which is assumed to have superior absolute accuracy and minimal residual systematic errors, are used for the Sentinel missions, while for the remaining missions orbit products by Centre National D’Etudes Spatiales (CNES) are used.

Eventually, starting from the DORIS only solutions, weekly local terrestrial reference frames (TRFs), are computed for each single satellites, as well as a combined solution for the entire analysis interval with all satellite missions is generated.

The TRF solutions thus generated are evaluated with respect to the reference frame defining parameters, i.e. origin, scale, and orientation, in comparison to the a piori TRF.

How to cite: Anton, R., Patrick, S., Karl Hans, N., and Rolf, K.: DORIS based precise orbit and reference frame determination using multiple altimetry satellite missions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14501, https://doi.org/10.5194/egusphere-egu23-14501, 2023.

The ILRS contributed to the development of ITRF2020 via the combined products submitted to ITRS. The combined products were the result of the combination of individual AC contributions where a new approach in handling systematic errors at the stations was implemented. A set of a priori estimated mean biases was considered for the main period 1993-2020 that includes data from LAGEOS, LAGEOS-2 and the Etalons, whereas an adjusted 15-day average bias at each station for the 1983-1993 period was considered to accommodate systematic and target signature errors, if a priori mean biases were missing. The implementation of ITRF2020/SLRF2020 in SLR operational products required an extended version of the SSEM model, SSEM-X, which led to the finalization of a new DH file. Considering this updated set of long-term mean biases, all ACs produced a solution set based on models used for REPRO2020 and SLRF2020 as input to a combined product intended for the IERS RS/PC at USNO. These EOP series will be used for the calibration of EOP biases prior to the release the final version of the new Bulletin A. The new bias model SSEM-X will be publicly available and maintained current over the coming years.

How to cite: Luceri, V., Basoni, A., Sarrocco, D., Pavlis, E. C., Kuzmicz-Cieslak, M., Evans, K., Bloßfeld, M., and Bianco, G.: Implementation of ITRF2020 in the ILRS Operational Products, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15354, https://doi.org/10.5194/egusphere-egu23-15354, 2023.

The Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG) is a collaborative contribution of the global geodesy community to the observation and monitoring of the Earth System. Geodetic observation techniques and analysis infrastructures, as well as the high-quality geodetic products, provide the foundation upon which advances in Earth and planetary system sciences and applications are built.

One main objective of GGOS is to support actions and initiatives to communicate the value of Geodesy to society, as well as help to understand and solve complex issues facing the global geodetic community. Towards this objective, GGOS has completely redesigned its website, www.ggos.org, which serves as a “point of entry to geodesy” to facilitate discoverability and usability of geodetic data and products. This includes explanations about: IAG services, geodetic observations and geodetic products. With this, GGOS engages with diverse user communities to increase awareness of geodesy and the ever-expanding benefits of geodesy in every-day applications.

In addition, GGOS recently produced short videos to explain the applications and importance of geodesy to non-geodesists. The new “Discover GGOS and Geodesy” video is available on YouTube in multiple languages.

How to cite: Sehnal, M., Sánchez, L., Angermann, D., Craddock, A., and Miyahara, B.: GGOS’s Geodetic Information Portal: Linking Geodesy and Society, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1281, https://doi.org/10.5194/egusphere-egu23-1281, 2023.

Water levels from hydrodynamic models typically lack an absolute vertical reference, and can thus not be linked directly to digital elevation models to assess coastal floodrisks. Instead, most workarounds rely on tide gauges that are connected to the land-based vertical reference to establish this link. The lack of an absolute vertical reference also makes it impossible to directly assimilate observed total water levels into models as this requires both observed and modeled water levels to refer to the same vertical datum.

The first consequence underlines the urgency of realizing an international height reference system that is easily accessible to users and which is adopted as the vertical reference in global tide gauge datasets and digital terrain models. Indeed, the lack of such an international height reference frame makes it impossible to accurately determine the impact and risks of sea level rise and changes in extreme water levels due to climate change. Let alone that an agenda for adaptation measures can be drawn up. The second consequence limits the accuracy of modeled water levels as existing workarounds do not exploit the observed long-term mean water level variations. At the same time, the assimilation of total water levels imposes strong requirements to the accuracy of an international height reference frame. Hydrodynamic models are extremely sensitive to slopes in observed water levels. Even small erroneous slopes between tide gauges introduced by errors in the vertical referencing, impose false currents that in turn result in model instabilities.

In turn, hydrodynamic models offer great and unique opportunities to assist in the realization of an international height reference system. The difference between the observation-derived mean water level (MWL) at location B and the sum of the observation-derived MWL at location A and the model-derived mean water level difference between the two locations is a proxy for the datum shift between the height datums used at locations A and B. The asset and uniqueness of the technique referred to as ‘model-based hydrodynamic leveling’ lies in the fact that it allows to transfer a height datum over large water bodies without the need to acquire new measurements. In the Dutch Versatile Hydrodynamics project, we implemented the technique and combined the data with geopotential differences from spirit leveling/gravimetry to compute a new realization of the European Vertical Reference System (EVRS).

This presentation will i) explain and demonstrate the need for an international height reference system from the perspective of hydrodynamic modelers; ii) demonstrate the potential contribution of hydrodynamic models to the realization of such a height system using the results obtained in the Versatile Hydrodynamics project, and iii) outlines ideas for future work.

How to cite: Slobbe, C., Verlaan, M., Klees, R., and Afrasteh, Y.: Hydrodynamic modeling and the realization of an international height reference system - urgent need and potential contribution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1539, https://doi.org/10.5194/egusphere-egu23-1539, 2023.

The frequency accuracy of optical atomic clocks has dramatically increased over the past 15 years, improving by more than two orders of magnitude from 16 digits of precision to 18 or even 19 digits of precision. Since around 2015 researchers from around the world began to consider a redefinition of the second that uses optical atomic clocks. Since then, the development of optical atomic clocks has progressed and the recent results demonstrated to detect the frequency change with 18 digits of precision.

The National Institute of Information and Communications Technology (NICT) has developed the Sr optical lattice clock and optical ion clocks employing In+ and Ca+, as well as a Sr optical lattice clock that provides calibration data to BIPM. On the other hand, the centimeter-level uncertainty of site elevation has caused 10^-18-level frequency uncertainties of optical frequency standards. Therefore, it is significantly important to understand frequency changes caused by solid-earth tides that often range from 10 to 20 cm in amplitude, by oceanic tidal loading, crustal deformations due to earthquakes, and ground movements with groundwater changes for the stable operation of optical atomic clocks.

NICT, in collaboration with partners including the Geospatial Information Authority of Japan (GSI), has begun observations and data analysis to evaluate how these effects interact with optical atomic clocks. Since early 2021, NICT and GSI have been jointly conducting leveling surveys and relative gravimeter observations at NICT’s headquarters in Koganei. These observations reduce the contribution of gravitational redshift to the total uncertainty of the NICT-Sr1 optical lattice clock has been reduced to the 10^-19 level.

With the support of National Institute of Polar Research (NIPR), absolute gravity measurements were performed in the August 2019 and May 2022 to evaluate the effects of  the 2011 March 11 Tohoku megaquake on coseismic vertical crustal movement. The obtained absolute gravity change between the two periods was -43.8 μGal. This matches the trend of GNSS result obtained by GSI, which show a vertical movement of up to 31.5 mm from August 2019 to May 2022, equivalent to about -10 μGal gravity change, even though the values do not agree precisely.

We have introduced a Micro-g LaCoste's gPhoneX gravimeter for continuous gravity measurements near by the optical clocks in the end of 2021. The preliminary results over seven months detects stable gravity change due to solid-earth tide with about 22 μGal precision. In addition, we have started to investigate the temporal variation of the ground water level at Koganei. We are also monitoring vertical crustal movements by geodetic GNSS measurements. We will investigate uncertainties of optical clocks due to vertical movements caused by geodetic phenomena using continuous gravity and GNSS measurements.

How to cite: Ichikawa, R., Hachisu, H., Sekido, M., Ido, T., Hiraoka, Y., Harima, E., Fukaya, S., Nakashima, M., Matsuo, K., Aoyama, Y., Hattori, A., and Fukuda, Y.: Geodetic measurements and quantitative evaluation for reduced gravitational redshift uncertainty of NICT optical frequency standards, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2983, https://doi.org/10.5194/egusphere-egu23-2983, 2023.

Time-variations in the orientation of the solid Earth are largely governed by the exchange of angular momentum with the surface geophysical fluids of atmosphere, oceans, and the land surface. Modelled fields of atmospheric winds, atmospheric surface pressure, ocean currents, ocean bottom pressure, and terrestrial water storage allow to calculate effective angular momentum (EAM) functions that provide highly reliable information about the orientation changes of the Earth. EAM forecasts derived from model forecast runs support substantially short-term Earth Orientation Parameters (EOP) Predictions. So far, routinely available EAM forecasts do not include any error information needed for rigorous combination of EAM forecasts with EOP predictions from various geodetic techniques. Based on hindcast experiments, we analysed the EAM forecast error and trained a neural network to predict EAM forecast errors. As expected, EAM forecast errors increase with the prediction horizon but we found also irregular large variation in the EAM forecast error that seem to be well predictable with machine learning methods. 

How to cite: Dill, R. and Dobslaw, H.: Predicting Effective Angular Momentum Function Forecast Errors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3090, https://doi.org/10.5194/egusphere-egu23-3090, 2023.

Earth orientation parameters (EOPs) are currently determined from measurements taken by the space-geodetic techniques of SLR, VLBI, GNSS, and DORIS. But each technique has its own unique strengths and weaknesses in this regard. Not only is each technique sensitive to a different subset and/or linear combination of the EOPs, but the averaging time for their determination is different, as is the interval between observations, the precision with which they can be determined, and the duration of the resulting EOP series. By combining the individual series determined by each technique, a series of the Earth's orientation can be obtained that is based upon independent measurements and that spans the greatest possible time interval. Such a combined Earth orientation series is useful for a number of purposes, including a variety of scientific studies and as an a priori series for use in data reduction procedures. However, care must be taken in generating such a combined series in order to account for differences in the underlying reference frames within which each individual series is determined (which can lead to differences in the bias and rate of the Earth orientation series). Traditionally, differences in the underlying reference frames are accounted for by applying a correction to the bias and rate of each individual series being combined with the goal of placing the series within a common reference frame. But there is an uncertainty associated with estimating the bias and rate correction that needs to be applied to each series. In fact, this uncertainty is a major (if not the major) source of error in combined EOP series. However, this source of error can be mitigated by jointly combining the EOP series with the terrestrial reference frame. Recent ITRF and JTRF solutions such as ITRF2020 and JTRF2020 have included EOP series in their determination. In this presentation, the ITRF2020 and JTRF2020 combined polar motion series will be compared to the more traditionally determined IERS Bulletin A and JPL KEOF (Kalman Earth Orientation Filter) combined polar motion series in order to study the improvement attained by jointly determining the combined EOP series with the terrestrial reference frame.

How to cite: Gross, R., Abbondanza, C., Chin, M., Heflin, M., and Parker, J.: Improving Combined EOP Series by Jointly Determining Them with the Terrestrial Reference Frame, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3469, https://doi.org/10.5194/egusphere-egu23-3469, 2023.

Determination of Earth Orientation Parameters (EOP) with utmost accuracy requires the combination of various data sources from different space geodetic techniques, some of which requiring long processing time. This results in a latency of up to several weeks by which the so-called final EOP are released. Since some of the important applications, including satellite navigation and orientation of deep space telescopes, require instantaneous EOP information, the so-called rapid determination and also prediction of EOP are needed. International Earth Rotation and Reference Systems Service (IERS) provides rapid EOP by using the most recent Global Positioning System (GPS) and Very Long Baseline Interferometry (VLBI) 24-hour and intensive sessions data. However, there are some discrepancies between these rapid data and the final, most accurate EOP. In order to reduce these discrepancies and achieve more accurate rapid EOP, we focus on applying machine learning algorithms for polar motion components (xp, yp) and dUT1=UT1-UTC. We focus on a window of 63 days with 31 day predictions to the past and 31 day predictions to the future.

We devise a new algorithm called ResLearner, which is a machine learning method based on multilayer perceptrons trying to learn the differences between rapid and final EOP data. We use informative features such as Effective Angular Momentum (EAM) data (both the observations provided by GFZ and the 14-day forecasts provided by ETH Zurich), tides, Liouville equation for (xp, yp), and a linear relation between dUT1 and the axial components of EAM.
We use ResLearner in the context of Deep Ensembles in order to derive the uncertainty in the estimations. We also address the so-called unmixing and self-calibration problems. The former enables us to unravel the causes behind the discrepancies between rapid and final EOP as provided by IERS, while the latter could help us reduce these erroneous effects. 

We train the algorithms on both the IERS and Jet Propulsion Laboratory (JPL) final EOP data. Our ResLearner method can consistently reduce the discrepancies between rapid and final EOP across all days. The improvement in accuracy is up to 55%. We observe some unexpected behaviour related to day 0 of prediction, in which the accuracy of the IERS is significantly better than the immediately preceding or following values. Our unmixing algorithm shows that this behaviour is probably related to erroneous, non-linear effects of EAM at day 0, and also semi-diurnal, diurnal, long-period retrograde and prograde, and zonal tides. Using our self-calibration algorithm for EAM, we can slightly improve the prediction performance by up to 14%.

Finally, we provide the improved rapid EOP data publicly, operationally, and on a daily basis, on the ETH Zurich prediction center website at https://gpc.ethz.ch/EOP/Rapid/

How to cite: Kiani Shahvandi, M., Dill, R., Dobslaw, H., Mishra, S., and Soja, B.: Improving the accuracy of rapid Earth Orientation Parameters with the "ResLearner" machine learning method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4162, https://doi.org/10.5194/egusphere-egu23-4162, 2023.

The use of digital object identifiers (DOI) for scientific data and scientific software is increasingly common practice for more than a decade. As a result of the Coalition on Publishing Data in the Earth and Space Sciences (COPDESS) and other initiatives, DOI-referenced datasets are fully citable in scholarly literature and more and more journals require the availability of data underlying scientific results and their citation. Technical implementations, like Scholix (a framework for Scholarly Link Exchange) enable direct links and between literature and data and support the visibility of research data. Key elements for enabling these links are persistent identifier (PID). These PIDs allow, e.g., to uniquely identify data, scholarly literature and code (via DOIs), persons (via ORCID), institutions and funding agencies (via ROR – the registry of research organizations), via machine-actionable links and should be included in the DOI metadata.

Similar to other scientific disciplines, the use of DOI for geodetic data is increasing in the last years. While this is easy for static data, like for global of regional gravitational models or GNSS campaign data, most geodetic data are large (mainly due to the large number of files and high temporal resolution) and highly dynamic (real time data acquisition) and highly granular. Geodetic services of the International Association for Geodesy (IAG) are international key player for geodetic data provision and distribution and their operating institutions and funding agencies increasingly require the provision of tangible data use and access statistics. Credit through citation was a major reason for the Global Geodetic Observing System (GGOS) to establish a Working Group on using DOI for geodetic data sets (GGOS DOI WG) and for the working group members.

The GGOS DOI WG was established in 2019 and includes international representatives of IAG Services and geodetic data centres and associated members that aims at developing best practices and recommendations for the consistent implementation of DOIs across all IAG Services and in the greater geodetic community. This presentation will give an update on recent group activities and on the status of DOI minting for geodetic datasets across IAG Services.

How to cite: Elger, K. and the GGOS DOI Working Group: The world of DOIs for geodetic data – metadata recommendations and status report of the GGOS DOI Working Group, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6384, https://doi.org/10.5194/egusphere-egu23-6384, 2023.

Polar Motion is the movement of the Earth's rotational axis relative to its crust, reflecting the influence of the material exchange and mess redistribution of each layer of the Earth on the Earth's rotation axis.
The real-time estimation of Polar Motion (PM) is needed for the navigation of Earth satellites and interplanetary spacecraft. However, it is impossible to have real-time information due to the complexity of the measurement model and data processing.

Various prediction methods have been developed. However, the accuracy of PM prediction is still not satisfactory even for a few days in the future. Therefore, a new technique or a combination of the existing methods needs to be investigated for improving the accuracy of the prediction PM.
In this study, we combine the 1D  Convolutional Neural Network with the Singular Spectrum Analysis (SSA).
 The computational strategy follows multiple steps, first, we model the predominant trend of the PM time series using SSA. Then, the difference between the PM time series and its SSA estimation is modeled using the 1D Convolution Neural Network. However, we developed a Multivariate Multi step 1D-CNN Model with a Multi-output strategy to predict at the same time both components (Xp, Yp)  of the PM.  . We introduce to the  Model: the Ocean Angular Momentum, Atmospheric Angular Momentum, and Hydrological Angular Momentum (OAM+AAM+HAM) to improve the results. Multiple sets of PM predictions which range between 1 and 10 days have been performed based on an IERS 14 C04 time series to assess the capability of our hybrid Model. Our results illustrate that the proposed method can efficiently predict both (Xp, Yp) of PM.

How to cite: Guessoum, S., Belda, S., Ferrándiz, J. M., Modiri, S., Heinkelmann, R., Schuh, H., and Dhar, S.: The short-term prediction of Polar Motion using the combination of SSA and the Multivariate Multi-step 1D- Convolutional Neural Networks with Multioutput strategy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6737, https://doi.org/10.5194/egusphere-egu23-6737, 2023.

From the investigation of GRACE and GRACE-FO instrument data, we are aware of quite a number of unmodeled effects and deficiencies in the calibration of instruments. We want to use these deficiencies as an example to discuss how for a core GGOS observation technique, such as GRACE / GRACE-FO, all opportunities to assess and improve sensor calibration and to identify and characterize unmodeled effects affecting the measurements should be explored. This may seem obvious, but we will show that a major effort on this field would be very desirable. We deliberately choose the GGOS session for a broader discussion of the topic, and we want to highlight the importance of an overarching approach that combines insight from different satellite missions and space techniques.

How to cite: Flury, J., Koch, I., and Duwe, M.: Well calibrated space sensor systems for GGOS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8078, https://doi.org/10.5194/egusphere-egu23-8078, 2023.

The derivation and subsequent use of suitable corrections to the current IAU2006/IAU2000 precession/nutation models is a main objective of the IAU/IAG Joint Working Group on Improving theories and models of the Earth rotation (JWG ITMER). It has been recognized in the latter IERS/GGOS Unified Analysis Workshops as the fastest way of improving the accuracy of those models at the short-term and thus contributing to the development of the last Resolutions of the IAG and IAU on Earth rotation.

In the last few years, some research groups have proposed different sets of corrections or updates to precession and either the forced or free nutations – including alternative approaches to free core nutation (FCN) models. The derivations of the various sets are related to VLBI solutions or observational data to quite different extents. The purpose of this study is providing a wider view into the performance of such corrections, focusing on features and capabilities more directly related to VLBI data analysis

How to cite: Ferrándiz, J. M., Karbon, M., Belda, S., and Escapa, A.: On the performance of the corrections to the current precession-nutation models in VLBI data analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8821, https://doi.org/10.5194/egusphere-egu23-8821, 2023.

Consideration of the Free Core Nutation (FCN) is required to improve the modelling of the Celestial Pole Offsets (CPO) since it is the major source of inaccuracy or unexplained time variability with respect to the current IAU2000 nutation theory. The FCN is a free mode related to the non-alignment of the rotation axis of the core and of the mantle. It can only be measured/detected by Very Long Baseline Interferometry (VLBI). IERS Conventions (2010) recommends an empirical FCN model of Lambert (2007). However, other alternative models are available today (e.g. Krásná et al. 2013; Malkin 2013; Belda 2016). All these models are based on the sliding window least-squares fit method, assuming a constant period of about -430 solar days.

In our previous studies, we evidenced that the period of the FCN could vary with time. Due to this FCN period variability, the conventional empirical FCN models would not be completely correct. Therefore, should we find out new mathematical approaches/strategies to model the FCN?

In this study, a new mathematical strategy is examined. We utilized the Whittaker smoother to extract the desired signal from the CPO series obtained from VLBI. This technique tends to behave as highly adaptive and versatile fitting algorithms and can thus replace conventional FCN models. Apart from that, it is extremely fast, gives continuous control over smoothness with only one parameter (lambda), interpolates automatically, and allows fast leave-one-out cross-validation. The preliminary assessment using the observed nutations derived from VLBI analysis demonstrated the potential of Whitaker smoother as an optimum algorithm to successfully reconstruct the FCN signal with more efficient performance to retrieve reliable patterns. This analysis could bring us significantly closer to meeting the accuracy goals pursued by the Global Geodetic Observing System (GGOS).

How to cite: Belda, S., Karbon, M., Escapa, A., Puente, V., Modiri, S., and Ferrándiz, J. M.: Should we find out new mathematical strategies to model the Free Core Nutation?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10034, https://doi.org/10.5194/egusphere-egu23-10034, 2023.

How to cite: Nagae, K., Ishikawa, T., Watanabe, S., Nakamura, Y., and Yokota, Y.: Various error factors in GNSS-A seafloor geodetic observation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11203, https://doi.org/10.5194/egusphere-egu23-11203, 2023.

The Global Geodetic Observing System (GGOS) is a collaborative contribution of the global Geodesy community to the observation and monitoring of the Earth System. Geodesy is the science of determining the shape of the Earth, its gravity field, and its rotation as functions of time. Essential to reach this goal are stable and consistent geodetic reference frames, which provide the fundamental layer for the determination of time-dependent coordinates of points or objects, and for describing the motion of the Earth in space. With modern instrumentation and analytical techniques, Geodesy is capable of detecting time variations ranging from large and secular scales to very small and transient deformations – all with increasing spatial and temporal resolution, high accuracy, and decreasing latency. The geodetic observational and analysis infrastructures as well as the high-quality geodetic products provide the foundation upon which advances in Earth and planetary system sciences and applications are built. In this way, GGOS endeavors to facilitate and enable production and sharing of the Earth observations needed to monitor, map, and understand changes in the Earth’s shape, rotation, and mass distribution. GGOS also advocates the global geodetic frame of reference as the fundamental backbone for measuring and consistently interpreting global change processes as well as the essential geospatial infrastructure to ensure a homogeneous and sustainable development worldwide.

GGOS closely works with its parent organization, the International Association of Geodesy (IAG), to keep these fundamental geodetic contributions sustainable. The IAG Services provide the infrastructure and products on which all contributions of GGOS are based, and the IAG Commissions and IAG Inter-Commission Committees provide expertise and support to address key scientific issues within GGOS. Additionally, GGOS supports the IAG by strengthening external and interdisciplinary relations and contributions to the broader geospatial information community, including relevant United Nations groups, in particular, the UN Committee of Experts on Global Geospatial Information Management (GGIM), its Subcommittee on Geodesy, and the new UN Global Geodetic Centre of Excellence (scheduled to commence operations in 2023). The main contribution of GGOS in this regard is to support actions and initiatives to communicate the value of Geodesy to society as well as to help to understand and solve complex issues facing the global geodesy community. Towards this objective, GGOS have developed a comprehensive Geodesy portal (https://ggos.org/) including detailed descriptions of geodetic observations (https://ggos.org/obs/) and products (https://ggos.org/products/), and various outreach tools such as short videos to explain the roles and importance of Geodesy to non-geodesists.

How to cite: Miyahara, B., Sánchez, L., Sehnal, M., and Craddock, A.: The Global Geodetic Observing System (GGOS) - infrastructure underpinning Science and Society -, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11302, https://doi.org/10.5194/egusphere-egu23-11302, 2023.

The GNSS-Acoustic ranging combination technique (GNSS-A) is a method to precisely measure the absolute position of the seafloor benchmark in the centimeter level by combining GNSS and acoustic ranging. The Hydrographic and Oceanographic Department of the Japan Coast Guard (JCG) has been conducting GNSS-A observation at 27 seafloor sites along the Japan Trench and the Nankai Trough named the Seafloor Geodetic Observation Array (SGO-A), to reveal the geophysical processes related to megathrusts that occur at the subduction zones along the Japanese archipelago. From the observations at the SGO-A sites along the Japan Trench, we have discovered the co- and postseismic processes of the 2011 Tohoku-oki Earthquake (Sato et al. 2011; Watanabe et al. 2021). Heterogeneous interplate coupling (Yokota et al. 2016) and shallow slow slip events (Yokota and Ishikawa 2020) have been revealed by observation along the Nankai Trough.

Currently, JCG conducts routine analysis using the open-source GNSS-A analysis software GARPOS (Watanabe et al. 2020). We are aiming an “open” GNSS-A, and the SGO-A coordinate time series obtained from the routine analysis are published online. In this presentation, we review our observation and analysis methods, and discuss on the latest observation results obtained at the SGO-A sites. Additionally, we also introduce our GNSS-A data format, which we have been discussing in the seafloor geodesy data standardization task force of the Inter-Commission Committee on Marine Geodesy (ICCM) in the International Association of Geodesy.

How to cite: Nakamura, Y., Watanabe, S., Ishikawa, T., Nagae, K., and Yokota, Y.: Japan Coast Guard's GNSS-A seafloor geodetic observation: analysis scheme and development of data format, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11358, https://doi.org/10.5194/egusphere-egu23-11358, 2023.

Measuring, studying, and understanding global change effects demand unified geodetic reference frames with (i) an order of accuracy higher than the magnitude of the effects to be observed, (ii) consistency and reliability worldwide, and (iii) long-term stability. The development of the International Terrestrial Reference System (ITRS) and its realisation, the International Terrestrial Reference Frame (ITRF), enable the precise description of the Earth’s geometry by means of geocentric Cartesian coordinates with an accuracy at the cm-level and with global consistency. An equivalent high-precise global height reference system that provides the basis for the consistent determination of gravity field-related coordinates worldwide, in particular geopotential differences or physical heights, is missing. Without a conventional global height system, most countries rely on local height systems, which have been implemented individually, applying in general non-standardised and non-uniform procedures. It is proven that their combination in a global frame presents discrepancies at the metre level. Therefore, a core objective of the international geodetic community is to establish an international standard for the precise determination of physical heights. This standard is known as the International Height Reference System (IHRS). Its realisation has been a main topic of research during the last years. Recent achievements concentrate on (1) compiling detailed standards, conventions, and guidelines for the IHRS realisation, (2) evaluating computational approaches for the consistent determination of potential differences, and (3) designing an operational infrastructure that ensures the maintenance and long-term stability of the IHRS and its realization. This contribution summarises advances and current challenges in the establishment, realization and sustainability of the IHRS.

How to cite: Sanchez, L., Huang, J., Barzaghi, R., and Vergos, G. S.: Advances in the determination of a global unified reference frame for physical heights, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12049, https://doi.org/10.5194/egusphere-egu23-12049, 2023.

As the unique approach to obtain centimeter-level seafloor positioning information, Global Navigation Satellite System-Acoustic ranging combination technique (GNSS-A) (Spiess, 1985) has drawn increasing attention and plays an important role in ocean engineering and marine geoscience research (Gagnon et al. 2005; Tadokoro et al. 2006; Watanabe et al.2014; Yokota et al. 2016; Yang et al. 2018).

GNSS-A positioning accuracy is significantly restricted by temporal and spatial variation errors related to propagation velocity of acoustic signals, the bridge medium to connect sea-surface platform and seafloor stations. Valuable investigations focusing on sound speed structure (SSS) modelling and inversion have been released and contribute to the GNSS-A performance improvements (Fujita et al. 2006; Ikuta et al. 2008; Honsho et al. 2017; Yokota et al. 2019; Watanabe et al. 2020; Yang et al. 2020; Yokota et al, 2022; Xue et al. 2023, in prep). It’s promising to progressively suppress SSS errors effect on seafloor positioning capability based on the increasingly refined SSS model policy.

Besides concentration on SSS errors modeling and corrections, additional consideration of positional uncertainty of sea-surface platform, one of vital parts of entire GNSS-A observation system, is reasonable for refined seafloor positioning policy. Currently, joint/total adjustment model and parameter estimation of the transducer and seafloor transponder for underwater precise point positioning have been published (Zhao et al. 2021). Furthermore, for seafloor geodetic network scene, numerical tests considering the positional uncertainty of sea-surface transducer were conducted. Further research may be hopeful to evaluate and control error propagation effect on seafloor positioning from sea-surface segment and helpful for usage of more flexible platform.

How to cite: Zhao, S. and Yokota, Y.: Consideration of positional uncertainty of sea-surface platform for GNSS-A seafloor positioning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12103, https://doi.org/10.5194/egusphere-egu23-12103, 2023.

The motion of the Earth's pole is excited by processes internal to the Earth's system – continually changing mass distribution in the geophysical fluids, i.e., atmosphere, ocean, and land hydrology. The mass redistribution and its movements within the Earth system excite the Earth's rotational changes mainly at seasonal or shorter timescales. The importance of atmospheric and oceanic angular momentum (AAM, and OAM, respectively) signals for polar motion excitation at seasonal and interannual timescales is well known. However, previous studies showed that the AAM, computed from different models of atmospheric pressure changes and winds, slightly differ from each other, especially in ­χ1 component. The discrepancies between various representations of ocean bottom pressure and currents from different OAM models are apparent too.

An essential technique for understanding Earth's rotational changes is comparing the sum of mass and motion terms of AAM and OAM based on different geophysical models.

Up to now, studies of geophysical excitations of polar motion containing AAM, OAM, and hydrological angular momentum (HAM) have not achieved entire agreement between geophysical (sum of AAM, OAM, and HAM obtained from the models) and geodetic (GAM, geodetic angular momentum; obtained from geodetic measurements of polar motion) excitation. There are many geophysical models of the atmosphere, oceans, and land hydrology that can be used to compute polar motion excitation. However, these models are very complex and still suffer from uncertainties in the process descriptions, parametrization, and forcing.

Until now, no studies have shown that selecting one particular combination of AAM+OAM models provides the best correlation with GAM. The choice of AAM and OAM time series is usually entirely arbitrary and the only criterion considered is that the AAM model should be combined with the OAM model in which the forcing data is taken from the  AAM model used. 

This analysis of the most recent AAM and OAM series highlights that hydrological signals in polar motion differ significantly. The main goal of this presentation is to demonstrate that using different combinations of mass and motion terms of both AAM and OAM may have a considerable influence on the geophysical excitation of polar motion and its consistency with GAM. In this study, we extend the present understanding of the problem of inconsistency of mass and especially motion terms of different AAM and OAM models at seasonal and non-seasonal time scales.

How to cite: Wińska, M., Śliwińska, J., and Nastula, J.: Comparison between polar motion excitation functions estimated from different models of geophysical fluids, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12366, https://doi.org/10.5194/egusphere-egu23-12366, 2023.

We present BKG´s current activities in the area of combined data processing of different space-geodetic techniques. The primary goal of the combined analyses is the improvement of the consistency between the techniques through common parameters, mainly Earth Rotation Parameters (ERP), and thereby to improve also the resulting ERP. In previous studies, we have investigated different combination approaches using VLBI and GNSS data and generated ERP time series with latencies of about 1-2 or 14 days, depending on the input data we used. In this way, we achieved a significant improvement in accuracy, especially for the dUT1 series, compared to the individual technique-specific solutions. The processing is based on homogenized datum-free normal equations (provided via SINEX files), which allow a rigorous combination on the normal equation level instead of the observation level.

Our main objective is to generate an ERP product that is characterized by a continuous, daily and regular resolution and the shortest possible latency, especially for the highly variable dUT1. The mandatory requirement for achieving these characteristics is the rapid availability of the input data on the daily basis, especially of the VLBI Intensive sessions. The time series of daily SINEX files of the legacy (S/X) VLBI Intensive sessions show some gaps in the past. The reasons for this are manifold and can be found throughout the entire VLBI processing chain, i.e., from the observation, i.e. station ability to participate, to the analysis, i.e. the data quality revision. However, in the last two years, an increasing number of VGOS Intensive campaigns has been conducted in addition to the legacy Intensives. As a result, the Intensive series is nowadays almost without gaps and there are even more than one Intensive sessions (up to 6) available per day. In our recent studies, we compare the VGOS and legacy Intensives data in terms of their latency and the quality of the resulting dUT1 estimates and integrate them into our combination process. We highlight also the challenges of extending the combination with the new VGOS data. Its incorporation will eventually pave the way for establishing an operational ERP product at BKG.

How to cite: Klemm, L., Thaller, D., Flohrer, C., Walenta, A., Ullrich, D., and Hellmers, H.: Improving the temporal regularity and continuity of consistently combined ERP: A closer look at today’s VLBI Intensives., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13073, https://doi.org/10.5194/egusphere-egu23-13073, 2023.

The Bureau of Products and Standards (BPS) is a key component of the Global Geodetic Observing System (GGOS) of the International Association of Geodesy (IAG). It supports GGOS in its goal to provide consistent geodetic products needed to monitor, map, and understand changes in the Earth’s shape, rotation, and gravity field. In its current structure, the Committees “Contributions to Earth System Modeling” and “Definition of Essential Geodetic Variables” as well as the Working Group “Towards a consistent set of parameters for the definition of a new Geodetic Reference System (GRS)” are associated to the BPS.

This poster contribution presents the role of the BPS and it highlights some of the recent activities, which are focused on the updating of the IERS Conventions, mainly related to Chapter 1 "General definitions and numerical standards", the updating of the BPS inventory of standards and conventions used for the generation of IAG products to incorporate the latest developments in the field, the compilation of user-friendly descriptions of geodetic products published at the GGOS website, and the contribution to GGOS films for specific products. The BPS activities also comprise the interaction with IAG and other entities in the field of standards and conventions, such as the IAG Services, the IERS Conventions Center, the Commission A3 “Fundamental Standards” of the International Astronomical Union (IAU), ISO/TC 211 and the Working Group ``Data Sharing and Development of Geodetic Standards” of the UN-GGIM Subcommittee on Geodesy (SCoG).

How to cite: Angermann, D., Gruber, T., Gerstl, M., Heinkelmann, R., Hugentobler, U., Sanchez, L., and Steigenberger, P.: Role and Activities of the GGOS Bureau of Products and Standards, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13114, https://doi.org/10.5194/egusphere-egu23-13114, 2023.

High-resolution regional applications require regional reference frames with dense networks of reference stations. These regional reference frames can be realised in the form of multi-year reference frames (that can be fixed to a specific tectonic plate like EUREF for Europe) or as epoch reference frames to represent non-linear phenomena such as earthquakes or loading effects (like SIRGAS for Latin America). Common to these realisations is that they are based on GNSS networks with a geodetic datum that is realised by alignment to the global reference frame (ITRF or IGS TRF).

In consequence, the origin of these networks reflects the Earth’s centre of figure rather than the Earth’s instantaneous centre of mass. Moreover, the quality of the realised datum decreases over time, as the linearly-parameterised coordinates of the global reference frame have to be extrapolated beyond the observation period. These effects mean a significantly reduced value of station-specific displacement time series for the study of, e.g., local geophysical effects.

This study presents an alternative approach for the realisation of a regional epoch reference frame for Latin America. The approach is based on the common weekly solution of global SLR, VLBI and GNSS networks combined at the normal equation level. Thereby, SLR determines the origin, SLR and VLBI jointly determine the scale, and a homogeneously distributed global GNSS network is used to realise the orientation. This GNSS network is densified by the stations of the regional sub-network, namely the stations of the Latin American SIRGAS network. The approach does not necessarily rely on fiducial points in the region of interest, which means that it is conceptually transferrable to other regional networks.

In order to cope with system-specific deficiencies of SLR and VLBI, namely data gaps, low station performances and frequently changing observational networks deteriorating the realised datum parameters, we propose a strategy to stabilise the realised datum via filtering the input data of these techniques at the normal equation level before combination with GNSS.

We evaluate the realised datum of the epoch-wise weekly solutions by comparison against the ITRF2014 as an independent multi-year realisation of the ITRS and against the JTRF2014 as an independent sub-secular realisation of the ITRS. Moreover, station-specific displacement time series are validated against non-tidal loading displacement time series derived from geophysical fluid models provided by ESMGFZ in order to demonstrate that the displacement time series reflect seasonal geophysical processes in a geocentric frame.

How to cite: Kehm, A., Sánchez, L., Bloßfeld, M., Seitz, M., Drewes, H., Angermann, D., and Seitz, F.: Combination strategy for regional geocentric epoch reference frames, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13216, https://doi.org/10.5194/egusphere-egu23-13216, 2023.

Earth Orientation Parameters (EOP) represent the rotational part of the transformation between the current releases of the International Celestial Reference Frame (ICRF) and the International Terrestrial Reference Frame (ITRF). The determination of EOPs requires post-processing of observational data collected from various space geodetic techniques, which causes some delays in the provision of EOP solutions.

In the light of the developments in the field of advanced geodetic data processing, modelling effective angular momentum functions and developing new prediction methods, a re-assessment of the various EOP predictions is currently pursued in the frame of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC). The campaign started in September 2021 and its main part finished on 28 December 2022. It was run by the Centrum Badań Kosmicznych Polskiej Akademii Nauk in cooperation with GeoForschungsZentrum and under the auspices of the International Earth Rotation and Reference Systems Service (IERS).

In this presentation, we provide initial analysis of the impact of the choice of reference series used on the assessment of predictions submitted to the 2nd EOP PCC. We will compare the single-technique EOP series provided by International Global Navigation Satellite Systems Service (IGS), International Laser Ranging Service (ILRS), International Very Long Baseline Interferometry Service (IVS) as well as selected combined series with reference to official IERS solutions (IERS 14C04) for respective EOPs. We also look closer to the input data exploited by campaign participants to process predictions by dividing them into subclasses. We conduct selected statistical analyses, including forecast horizons, to show variabilities caused by reference series. We also analyse the number of rejected predictions with use of beta parameter considering various references. Finally, we focus on Mean Absolute Error (MAE) computed for 10 days and 30 days of predictions to discuss potential effects triggered by the input data choice. This work concludes with potential impacts of the input EOP data on the accuracy of the received EOP predictions.

How to cite: Partyka, A., Śliwińska, J., Kur, T., Nastula, J., Dobslaw, H., and Wińska, M. and the 2nd EOP PCC Participants: Impact of the reference series choice in analysis of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC) results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13472, https://doi.org/10.5194/egusphere-egu23-13472, 2023.

The Coupled Model Intercomparison Project Phase 6 (CMIP6) provides, amongst others, the Earth climate response to several different scenarios that simulate possible future anthropogenic drivers of climate change. The scenarios are characterized by different forcings, which are defined from a combination of plausible future societal developments, the Shared Socioeconomic Pathways (SSPs), and the Representative Concentration Pathways (RCPs), identified by the approximate radiative forcing level anticipated for 2100.

In a previous work, we investigated length of day variations induced by multi-model projections of zonal wind fields, stemming from historical simulations and from the four scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5. In order to cover the same set of five scenarios that are treated in the sixth assessment report of the Intergovernmental Panel on Climate Change, we add another low emission scenario, SSP1-1.9, in this follow-up study. Furthermore, we do not only assess the wind term but complete the analysis with the calculation of the respective atmospheric surface pressure terms. We are especially interested in the long-term variations and trends of length of day predicted for the period from 2015-2100 and the connection with variations and trends of the global surface temperature patterns. Regarding the excitation by zonal winds, preliminary assessments show that higher emission scenarios, which are associated with more intense global warming, would lead to a moderate increase in atmospheric angular momentum and thus to a proportional decrease of the Earth rotation rate.

How to cite: Böhm, S. and Salstein, D.: Atmospheric excitation of length of day inferred from 21st century climate model projections, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14040, https://doi.org/10.5194/egusphere-egu23-14040, 2023.

The accurate determination of Earth Orientation Parameters (EOP) requires post-processing of observational data collected from various space geodetic techniques, which causes delays in providing EOP solutions. However, receiving instantaneous information about EOP in real time is crucial in precise positioning and navigation. Therefore, EOP prediction (particularly short-term) has become a subject of increased attention within the international geodetic community.

In the light of the developments of advanced geodetic data processing, modelling effective angular momentum functions, and developing new prediction methods, a re-assessment of the various EOP predictions was pursued in the frame of the Second Earth Orientation Parameters Prediction Comparison Campaign (2^nd EOP PCC). The campaign was run by Centrum Badań Kosmicznych Polskiej Akademii Nauk (CBK PAN), in cooperation with GeoForschungsZentrum (GFZ) and under the auspices of the International Earth Rotation and Reference Systems Service (IERS). The campaign started on 1st September 2021 and finished on 28^th December 2022, giving 7327 submitted predictions within 82 weeks. The campaign was a great success of the geodetic community thanks to international cooperation.

The presentation provides the summary of the 2^nd EOP PCC. We focus on the recap of the statistics on the involved participants, i.e., the number of prediction methods and input data. Then we will present the accuracy of EOP predictions based on the mean absolute error computed for IERS 14 C04 solution as a reference. Additionally, we present the quality of predictions in clusters created from the campaign participants (IDs) based on their modern prediction methods combined with input data (EOP observations and data on the Earth’s surficial fluids) We conclude the presentations with plans for the prediction assessment, also in terms of the possible continuation of the campaign involving new release of IERS C04 20.

How to cite: Śliwińska, J., Kur, T., Nastula, J., Wińska, M., Dobslaw, H., and Partyka, A. and the 2nd EOP PCC Participants: Achievements of the Second Earth Orientation Parameters Prediction Comparison Campaign (2nd EOP PCC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14052, https://doi.org/10.5194/egusphere-egu23-14052, 2023.

Variations in Earth orientation parameters (EOP) are related to mass redistribution, gravitational, and geodynamic processes in the Earth system and have gained a great deal of attention in Earth science, astronomy, and climate change studies. In addition, real-time EOP information is needed for many space geodetic applications, including satellite navigation from the ground and low-Earth orbit, like tracking interplanetary spacecraft and forecasting the weather. Currently, the EOP can be estimated at the best possible accuracy with modern high-precision space geodetic techniques like Very Long Baseline Interferometry (VLBI), Global Navigation Satellite Systems (GNSS), and Satellite Laser Ranging (SLR). However, the complex nature of data processing and the time it takes to process it always lead to delays. Consequently, predicting EOP is of great scientific and practical importance. Accordingly, several methods have been developed and applied to EOP prediction. In spite of this, the accuracy of EOP still needs to meet our expectations, even for forecasts of a few days into the future. We will therefore have to face two major challenges in order to provide the best prediction data: which input data to use and which prediction methods are superior to others. In order to answer these two questions, new methods or a combination of existing approaches are investigated to improve the accuracy of the predicted EOP time seires. Such in-depth investigations are currently conducted within the “Second EOP Prediction Comparison Campaign (EOP-PCC)” organized by IAG and IERS. In this study, we investigate a redesigned prediction package (input data and method) to improve the possibility of bridging the existing gap between the observation and the final estimated product.

We will briefly present our contribution to EOP-PCC and illustrate the result of EOP data obtained from single space geodetic techniques provided by the department of geodesy at BKG. Then, we run our prediction algorithm with the official IERS EOP series and our BKG’s single-technique analysis products for VLBI and SLR using the combination of a deterministic and a stochastic method and compare it with different prediction techniques. Finally, we will show the potential of using a combination of VLBI and GNSS techniques to obtain real-time EOP estimates.

How to cite: Modiri, S., Thaller, D., Klemm, L., König, D., Hellmers, H., Bachmann, S., Flohrer, C., and Walenta, A.: EOP Prediction with special focus on using EOP products by different space geodetic techniques as input, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14827, https://doi.org/10.5194/egusphere-egu23-14827, 2023.

On 1 July 2023, the International DORIS Service (IDS) will celebrate the 20th anniversary of its creation under the umbrella of the International Association of Geodesy (IAG). The IDS was established to foster scientific research related to the French DORIS tracking system and to deliver scientific products, mostly related to the International Earth rotation and Reference systems Service (IERS). Since its start, the organization has continuously evolved, leading to additional and improved operational products. IDS is now based on a reinforced structure with two Data Centers, six Analysis Centers, four Associated Analysis Center, a Combination Center, and several partner groups.

The DORIS system recorded its first measurement on February 3rd, 1990, from the SPOT-2 remote sensing satellite. 32 years after, the system is at its best. DORIS has proven greatly valuable for geodesy and geophysics applications: measuring tectonic plate motions, determination of the rotation and the gravity parameters of the Earth, contributing to the international reference system, ... Technological and methodological improvements have allowed the improvement in the estimates of the positions of the DORIS tracking ground stations, the Earth rotation parameters and other geodetic variables such as the geocenter and the scale of the ITRF. This year, a 9th satellite joins the current constellation of DORIS satellites. It is SWOT, launched on 16 December 2022. Never before have so many DORIS instruments been in operation simultaneously.

This presentation addresses the recent achievements made by IDS and its components, and the future plans of the service.

How to cite: Soudarin, L., Lemoine, F., and Sellé, A.: The International DORIS Service: almost 20 years old., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15885, https://doi.org/10.5194/egusphere-egu23-15885, 2023.

This study investigates the reasons for the decrease in the water level of Beysehir Lake and the shrinkage in the lake's surface area in recent years. For this purpose, the lake water level was determined from multi-mission satellite altimeter data, and the lake area was calculated using high-resolution optical satellite images. Data from Copernicus Global Land Service was used for multi-mission satellite altimeter data, and the lake level trend between 1993-2022 was calculated with the least squares method. European Space Agency's (ESA) Sentinel-2 high-resolution optical images were used to determine the change in the lake surface area between 2015 and 2020. These high-resolution optical images were processed with The Sentinel Application Platform (SNAP) software. The Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI) were calculated based on processed optical images, and these indexes reflect the changes in water surface area. From the satellite altimeter data, a decreasing trend of 2.5 ± 0.5 cm/yr in the lake water level in the last ten years and shrinkage of approximately 8 km² in the last 6 years from the satellite images were determined. The possibility of one of the most important reasons being drought was emphasized, and monthly average air temperature data and monthly average precipitation data were obtained from the Turkish General Directorate of Meteorology. With these data, 3- and 12-month Standardized Precipitation Evapotranspiration Index (SPEI) were calculated. Regarding these calculated drought indexes, moderate, extreme, and severe hydrological drought has been determined in the region. According to the analysis, drought is thought to be the most important reason for the decrease in the lake water level and shrinkage in the lake surface area.

Keywords : Geodesy for Climate, Lake Water Level, Satellite Altimetry, In-situ observation, Sentinel-2

How to cite: Erkoç, M. H.: Examination of Causes for Decrease in the Water Level of Beysehir Lake and Shrinkage in the Lake's Surface Area., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-258, https://doi.org/10.5194/egusphere-egu23-258, 2023.

Gravity Recovery and Climate Experiment (GRACE) and GRACE-FollowOn (GFO) satellites can monitor the global spatio-temporal changes in terrestrial water storage anomalies (TWSA) with monthly temporal and ~300 km spatial resolutions. Since these native resolutions may not be adequate for various studies requiring better localization of TWSA signal both in spatial and temporal domains, in recent years, considerable efforts have been devoted to downscaling TWSA to higher resolutions. However, the majority of these studies have focused on spatial downscaling; only a few studies attempted to improve the temporal resolution. Here, we utilized an in-house developed Deep Learning (DL) based model to downscale the monthly GRACE/GFO Mass Concentration (Mascon) TWSA to daily resolution across the Contiguous United States (CONUS). The simulative performance of the DL algorithm is tested by comparing the simulations to independent (non-GRACE) dataset and the land hydrology models. In addition, we assessed the potential of our daily simulations to detect long- and short-term variations in TWSA. The validation results show that our DL-aided simulations do not overestimate or underestimate GRACE/GFO TWSA and can monitor variations in the water cycle at a higher temporal resolution.

How to cite: Uz, M., Akyılmaz, O., and Shum, C.: Deep Learning-aided Temporal Downscaling of Satellite GravimetryTerrestrial Water Storage Anomalies Across the Contiguous United States (CONUS), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-632, https://doi.org/10.5194/egusphere-egu23-632, 2023.

The interpretation of hydrospheric changes in the context of climate change can be enhanced using Global Navigation Satellite System (GNSS) displacement time series (DTS) combined with the one of a hydrological model. Our methodology is based on a computationally filtering strategy called the Savitzky-Golay filter and applied to selected stations in Europe. We use the GNSS solutions provided by the International GNSS Service (IGS) and, for the first time, the Nevada Geodetic Laboratory (NGL). The new hybrid dataset shows a high correspondence with DTS derived from the Gravity Recovery and Climate Experiment (GRACE) gravity mission but allows the identification of local and station-specific effects. Prior to this analysis, we eliminate various effects such as non-tidal atmospheric and oceanic loadings, glacial isostatic adjustment, barystatic sea-level changes, or thermoelastic deformation from GNSS DTS.

How to cite: Kermarrec, G., Klos, A., Dobslaw, H., Bogusz, J., and Eicker, A.: Hydrospheric mass loading for Europe from GNSS vertical displacement and a hydrological model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1929, https://doi.org/10.5194/egusphere-egu23-1929, 2023.

With the intensification of global climate change, droughts have occurred frequently in the Yangtze River Basin (YRB), which has caused significant impacts on human production, life, and socio-economic development. To reduce the damage caused by drought in the YRB, the drought characteristics must be comprehensively detected and quantified. Here, the spatial and temporal variability of precipitation, runoff, soil moisture, terrestrial water storage, and groundwater in the YRB from the Gravity Recovery and Climate Experiment (GRACE), hydrological and in situ observations were comprehensively estimated by decomposing them into seasonal, subseasonal, trend, and interannual observations. The new weighted GRACE drought standardisation index (WGDSI) was reconstructed using the component contribution ratio and compared with the standardised soil moisture index (SSI), standardised precipitation index (SPI06), and standardisation runoff index (SRI). Additionally, the drought characteristics identified based on observations of the water storage deficit, severity, peak, duration, and recovery time were also quantified using the WGDSI over the YRB. The results indicated that changes in soil moisture, terrestrial water storage, and groundwater in the YRB increased from 2003 to 2019 and mainly based on seasonal and interannual signals. The correlation coefficients between the WGDSI and the SSI, SPI06, and SRI were 0.92, 0.62, and 0.79, respectively, which represented increases of 9%, 14%, and 21% compared to that with the unweighted GRACE drought standardisation index, respectively. The interannual variability of the hydrologic variables was more consistent with drought events in the YRB, which was beneficial for detecting drought. Two serious droughts occurred in the YRB from 2003 to 2019. In 2006, a continuous 7-month-long drought occurred, with a peak at -28.974 km³, severity of -174.767 km³∙month, average drought recovery rate of 0.83 km³/month, and recovery time of 30 months, while in 2011, a continuous 5-month-long drought occurred, with a peak at -18.384 km³, severity of -78.106 km³/month, average drought recovery rate of 0.40 km³/month and recovery time of 39 months. The above results indicate that the WGDSI can be used to monitor and quantify drought over the YRB. The index proposed in this study can be applied to generate new datasets and methods for detecting and quantifying global drought.

How to cite: Wan, X., Chao, N., Hu, Y., Wang, J., Liu, Z., and Zou, K.: Reconstructing a new terrestrial water storage deficit index to detect and quantify drought in the Yangtze River Basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2734, https://doi.org/10.5194/egusphere-egu23-2734, 2023.

One of the most dynamic components of Earth surface mass variability is the constant global redistribution of terrestrial water storage (TWS) across temporal scales of hours to decades. Mass loading and unloading from TWS changes induce instantaneous elastic deformation of the solid earth, producing predominantly vertical transient displacements that are observable by geodetic methods. The global expansion of Global Navigation Satellite Systems (GNSS) networks during the last decade have provided new opportunities of directly estimating changes in TWS at high spatial and temporal resolutions. While contemporary GNSS studies have demonstrated the ability to map regional-scale water storage variability, incorporating these geodetic TWS estimates with in-situ hydrologic measurements can provide further insights on the physical mechanisms underlying the terrestrial water cycle.

In this study, we investigate the potential of using GNSS-derived TWS estimates to infer individual watershed condition along California’s Sierra Nevada, a major water source for urban and agricultural use. Utilizing the dense GNSS network in the western United States, we invert vertical displacements for TWS change at subbasin scale spatial resolution (USGS HUC-8). Joint analysis of our TWS estimates and stream gauge data shows contrasting seasonal behaviours in the northern and southern Sierra Nevada. The snow-dominated southern section exhibits a significant time lag between maximum storage and maximum baseflow from March to May, indicating wet-season decoupling between surface storage and the subsurface reservoirs that drive baseflow. In contrast, the northern section exhibits little to no lag, indicative of persistent surface-to-subsurface coupling, consistent with the higher rain-to-snow ratio in the north. Furthermore, we demonstrate that GNSS-derived TWS estimates can be used to infer watershed antecedent storage conditions, in which interannual variability in summer storage (dry season) influences streamflow recession behaviours during early precipitation season. Continued development of GNSS-based water storage estimates and future assimilation with hydrologic models should provide additional understanding of the water budget and hillslope hydrology in the Sierra Nevada.

How to cite: Lau, N., Knappe, E., and Borsa, A.: Empirical GNSS-derived terrestrial water storage-streamflow relationship in the Sierra Nevada ranges, California, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4048, https://doi.org/10.5194/egusphere-egu23-4048, 2023.

For more than 30 years, the Global Navigation Satellite System (GNSS) has successfully detected local crust deformations. These changes in deformation are caused, among other things, by changes in Total Water Storage (TWS), which reflect regular changes in the water system, but are also coupled with changes resulting from unexpected climate change. Current water conflicts caused by climate variability, increased human activity, population growth and food demand are leading to an increased importance of monitoring the abundance of the terrestrial hydrosphere. Such monitoring is increasingly being carried out using GNSS observations, mainly due to the impressive number of permanent stations distributed on Earth. However, the distribution of GNSS stations is irregular, and the displacement time series is often incomplete. Moreover, because of systematic errors, consistency of several parameters estimated for nearby GNSS stations may be very low. To eliminate the impact of these errors, but still capture regular changes in the climate system, we estimated drought severity index (DSI) using GNSS displacement time series over Europe, and interpolated these station-based DSI values over European area in a 1 per 1 degree grid. The quality of interpolated GNSS-DSI values has been assessed using four external datasets: (1) the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) data, (2) combination of GRACE/-FO data with the Satellite Laser Ranging (SLR) data, provided by the University of Bonn, (3) combination of SLR data and high-low Satellite-To-Satellite Tracking (hlSST) data, provided by Leibniz University Hannover, and (4) the self-calibrating Palmer Drought Severity Index (scPDSI). The external datasets have low spatial resolution, when compared to station-dependent GNSS-DSI and the scPDSI index is unable to capture several real water changes. Using GNSS displacements for estimated of DSI reduces these limitations. Our results show that GNSS-based DSI is spatially coherent with indicators derived from other datasets and is able to map dry and wet periods occurring over Europe. GNSS-DSI are also able to capture extreme short events not observed by other datasets. We note that the GRACE-DSI values show the least consistency with GNSS-DSI values. We find also that the DSI values estimated from combined GRACE and SLR indices have largest root-mean-square values for Europe. Our results show that GNSS displacements can be applied to study human and/or climate impact on water changes in small spatial and temporal scales, which may be averaged out in the other datasets; this hold the true especially in regions where GNSS stations are densely distributed.

How to cite: Lenczuk, A., Klos, A., and Bogusz, J.: Quality assessment of the gridded climate indices estimated from GNSS displacements for the European area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4288, https://doi.org/10.5194/egusphere-egu23-4288, 2023.

Rapid melting of ice sheets and glaciers drives a unique geometry, or fingerprint, of sea-level change, including a sea-level fall in the vicinity of the ice sheet that is an order of magnitude greater than the associated global mean sea-level rise of the melt event. The detection of individual fingerprints has been challenging due to sparse sea surface height measurements at high latitudes and the difficulty of disentangling ocean dynamic variability from the signal. Efforts to date have analyzed sea level records outside the zone of major sea-level fall, where the gradients and amplitudes of the fingerprint signal are significantly lower. We predict the fingerprint of Greenland Ice Sheet (GrIS) melt using new ice mass loss estimates from radar altimetry data and model reconstructions of nearby glaciers, and compare this prediction to an independent, altimetry-derived sea surface height trend corrected for ocean dynamic variability in the region adjacent to the ice sheet. The two fields show consistent gradients across the region, with the expected strong drawdown of the sea surface toward GrIS. A statistically significant correlation between the two fields (p < 0.001) provides the first unambiguous observational detection of the near-field sea level fingerprint of recent GrIS melting in our warming world. This detection provides a robust map of the impact of ice mass flux on global oceans since the early 1990s, and validates theoretical and numerical developments in the sea level modelling community.

How to cite: Coulson, S., Dangendorf, S., Mitrovica, J. X., Tamisiea, M., Pan, L., and Sandwell, D.: A Detection of the Sea Level Fingerprint of Greenland Ice Sheet Melt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4554, https://doi.org/10.5194/egusphere-egu23-4554, 2023.

The satellite mission Gravity Recovery And Climate Experiment (GRACE) provided and its successor GRACE-FollowOn (GRACE-FO) provides a great opportunity to derive observations of the global water cycle from space. The missions have contributed and largely increased our knowledge about various hydrological processes on Earth, for example the melting of glaciers in Greenland or groundwater depletion in India. Nonetheless, the spatial resolution of about 300 km, missing months in the time series and the multi-month gap between GRACE and GRACE-FO complicate or even impede the usage in some applications. Further, separating single storage information, e.g. groundwater, from the GRACE/-FO derived total water storage anomalies (TWSA) is still difficult.

In recent decades, data assimilation techniques were used to downscale and disaggregate the GRACE/-FO TWSA, however, to our knowledge they focus on hydrological instead of geodetic applications, only a few assimilate GRACE/-FO TWSA on a global scale and open access is rare. Therefore, we provide the new Global Land Water Storage (GLWS2.0) data set that offers total water storage anomalies on a 0.5° monthly grid covering the global land except Greenland and Antarctica for the time period 2003 to 2019 without missing months and the GRACE/GRACE-FO gap and will soon be publicly available. GLWS2.0 is derived by assimilating GRACE and GRACE-FO TWSA into the WaterGAP model using the Ensemble Kalman Filter considering uncertainties.

We contrast the GLWS2.0 data with the GRACE/-FO observations and the model simulations in the spatial domain via linear trends, annual amplitudes and non-seasonal TWSA and in the spectral domain via degree variances, c20 coefficients and other representation of spherical harmonics. Worldwide, 1030 GNSS stations are used to validate GLWS2.0 by analyzing the vertical loading at short-term, seasonal and long-term temporal bands and we find that GLWS2.0 agrees better with GNSS than GRACE/-FO. In addition, a good agreement to another global data assimilation product is found, which assimilates GRACE/-FO TWSA into the Catchment Land Surface Model by NASA’s Goddard Space Flight Center.

How to cite: Gerdener, H., Kusche, J., Schulze, K., Döll, P., and Klos, A.: The global land water storage data set GLWS 2.0: assimilating GRACE and GRACE-FO into a global hydrological model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5086, https://doi.org/10.5194/egusphere-egu23-5086, 2023.

The Gravity Recovery and Climate Experiment (GRACE) mission has monitored total water storage anomalies (TWSA) globally with unprecedented resolution and accuracy since 2002. However, many applications require a data-based, multi-decadal extended record of TWSA prior to the GRACE period as well as bridging the eleven-months gap between GRACE and its successor GRACE-FO. Statistical and machine-learning 'reconstruction' approaches have been developed to this end, mostly via identifying relations of GRACE-derived TWSA to climate variables, and some regional or global land data sets are now publicly available.

In this contribution, we  compare the two global reconstructions by HUMPHREY AND GUDMUNDSSON (2019) and LI ET AL. (2021) mutually and against output from the the WaterGAP hydrological model from 1979 onwards, against large-scale mass-change derived from geodetic satellite laser ranging from 1992 onwards, and finally against differing GRACE/-FO solutions from 2002 onwards. 

We find that the reconstructions agree surprisingly well in many regions at seasonal and sub-seasonal timescales, even in the pre-GRACE era. We find larger differences at inter-annual timescales which we speculate are in part due to the way reconstructions are trained and in part on which specific GRACE solution they are trained as well as the climatological characteristic of the region. Our comparisons against independent SLR data reveal that reconstructions (only) partially succeed in representing anomalous TWSA for regions that are influenced by large climate modes such as ENSO.

How to cite: Hacker, C.: How realistic are multi-decadal reconstructions of GRACE-like total water storage anomalies?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5486, https://doi.org/10.5194/egusphere-egu23-5486, 2023.

Global coupled climate models are important for predicting future climate conditions. Due to sometimes large and often systematic model uncertainties, it is crucial to evaluate the outcome of model experiments against independent observations. Changes in the distribution and availability of terrestrial water storage (TWS), which can be measured by the satellite gravimetry missions GRACE and GRACE-FO, represent an important part of the climate system. However, the use of satellite gravity data for the evaluation of coupled climate models has only very recently become feasible. Challenges arise, e.g., from the still rather short time series of satellite data and from signal separation issues related to GRACE/-FO observing all mass change including non-water related variations such as glacial isostatic adjustment. Apart from climate model uncertainties, these challenges might be the reason for a disagreement between the direction of linear water storage trends of models and observations in several regions of the world, one of them located in Eastern Canada.

This presentation will highlight the latest results achieved from our ongoing research on climate model evaluation based on the analysis of an ensemble of models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). We will focus on long-term wetting and drying conditions in TWS. Using an ensemble of 52 GIA models that differ in the applied ice history, solid Earth rheology, and numerical code, this presentation will discuss how GIA modeling uncertainty does influence (i) the determination of water storage trends from GRACE/FO data, and (ii) the (dis-)agreement between drying/wetting trends in satellite gravimetry and CMIP6 climate models. We will show that the apparent disagreement between observations and models in highly GIA-affected regions in North America crucially depend on the particular model chosen for reducing the GIA effect from the GRACE satellite data.

How to cite: Schawohl, L., Eicker, A., Bagge, M., and Dobslaw, H.: Influence of GIA uncertainty on climate applications from satellite gravimetry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5889, https://doi.org/10.5194/egusphere-egu23-5889, 2023.

We developed a methodology for deriving automated and continuous specific surface mass balance time series for fast moving parts of ice sheets and shelves (>10m/a) by an accurate and simultaneous estimation of continuous in-situ snow density, snow water equivalent (SWE), and snow deposition and erosion, averaged over an area of several square meters and independent on weather conditions. Reliable in-situ surface mass balance estimates are scarce due to limited spatial and temporal data availability. While surface accumulation can be obtained in various ways, conversion to mass requires knowledge of the snow density, which is more difficult to obtain.

A combined Global Navigation Satellite Systems reflectometry and refractometry (GNSS-RR) approach based on in-situ refracted and reflected GNSS signals is developed. The individual GNSS-RR methods have already been successfully applied on stationary grounds and seasonal snowpacks and are now combined and transferred to moving surfaces like ice sheets. We installed a combined GNSS-RR system in November 2021 on the fast moving (~150m/d), high latitude Ekström ice shelf in the vicinity of the Neumayer III station in Antarctica. Continuous snow accumulation reference data is provided by a laser distance sensor at the same test site and manual density observations. Refracted and reflected GNSS observations from site are post-processed for SWE, snow accumulation, and snow density estimation with a sub-daily temporal resolution. Preliminary results of the first year of data show a high level of agreement with reference observations, calculated from snow accumulation data collected by the laser distance sensor and linearly interpolated monthly snow density observations of the uppermost layer equivalent to the height of snow above the buried antenna.

The deployed devices are geared towards prototype applications for reliable low-cost applications, which will allow large-scale retrieval of surface mass balance for general cryospheric applications, not only on ice sheets or shelves, but also sea ice. Regional climate models, snow modelling, and extensive remote sensing data products will profit from calibration and validation based on the derived field measurements, once such sensors can be deployed on larger scales.

How to cite: Steiner, L., Schmitthüsen, H., Wickert, J., and Eisen, O.: Combined GNSS Reflectometry/Refractometry for Continuous In Situ Surface Mass Balance Estimation on an Antarctic Ice Shelf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6919, https://doi.org/10.5194/egusphere-egu23-6919, 2023.

Global Navigation Satellite System (GNSS) is now an established observing system for atmospheric water vapour with high spatiotemporal resolution. Water vapour is under-sampled in the current climate-observing systems and obtaining and exploiting more high-quality humidity observations is essential for climate monitoring.

The Global Climate Observing System (GCOS), supported by the World Meteorological Organization (WMO), is establishing a reference climate observation network, the GCOS Reference Upper Air Network (GRUAN). Currently, this network comprises 30 reference sites worldwide, designed to detect long-term trends of key climate variables such as temperature and humidity in the upper atmosphere. GRUAN observations are required to be of reference quality, with known biases removed and with an associated uncertainty value, based on thorough characterization of all sources of measurement. In support of these goals, GNSS precipitable water (GNSS-PW) measurement has been included as a priority one measurement of the essential climate variable water vapor. The GNSS-PW program produces a nearly continuous reference measurement of PW and is therefore a substantial part of GRUAN.

GFZ contributes to GRUAN with its expertise in processing of ground-based GNSS network data to generate precise PW products. GFZ hosts a central processing facility for the GNSS data and is responsible for the installation of GNSS hardware, data transfer, processing and archiving, as well as derivation of GNSS-PW products according to GRUAN requirements including PW uncertainty estimation. Currently half of the GRUAN sites are equipped with GNSS receivers. GNSS-PW products for GRUAN and the results of validation studies will be presented.

How to cite: Dick, G., Zus, F., Wickert, J., Männel, B., and Bradke, M.: GNSS-derived Precipitable Water Vapor for Climate Monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7836, https://doi.org/10.5194/egusphere-egu23-7836, 2023.

We investigate the performances of GRACE and GRACE Follow-On satellite gravimetry missions in assessing the ocean mass budget at global scale over 2005-2020. For that purpose, we focus on the last years of the record (2015-2020) when GRACE and GRACE Follow-On faced instrumental problems. We compare the global mean ocean mass estimates from GRACE and GRACE Follow-On to the sum of its contributions from Greenland, Antarctica, land glaciers, terrestrial water storage and atmospheric water content estimated with independent observations. Significant residuals are observed in the global mean ocean mass budget at interannual time scales. Our analyses suggest that the terrestrial water storage variations based on global hydrological model likely contributes to a large part to the misclosure of the global mean ocean mass budget at interannual time scales. We also compare the GRACE-based global mean ocean mass with the altimetry-based global mean sea level corrected for the Argo-based thermosteric contribution (an equivalent of global mean ocean mass). After correcting for the wet troposphere drift of the radiometer on-board the Jason-3 altimeter satellite, we find that mass budget misclosure is reduced but still significant. However, replacing the Argo-based thermosteric component by the ORAS5 ocean reanlaysis or from CERES top of the atmosphere observations leads to closure of the mass budget over the 2015-2020 time span. We conclude that the two most likely sources of error in the global mean ocean mass budget are the thermosteric component based on Argo and the terrestrial water storage contribution based on global hydrological models. The GRACE and GRACE Follow-On data are unlikely to be responsible on their own for the non-closure of the global mean ocean mass budget.

How to cite: Barnoud, A., Pfeffer, J., Cazenave, A., Fraudeau, R., Rousseau, V., and Ablain, M.: Revisiting the global mean ocean mass budget over 2005-2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8001, https://doi.org/10.5194/egusphere-egu23-8001, 2023.

Satellite gravity missions have been almost continuously observing global mass transports for more than two decades. The resulting data record already improved our understanding of large-scale processes of the water cycle and is reaching a timespan, which has significance concerning climate related mass transport signals such as changes in the essential climate variables terrestrial water storage (TWS) and sea level. The observations of the currently flown GRACE-FO mission will be continued by NASA’s Mass Change (MC) Mission and extended to the Mass change And Geosciences International Constellation (MAGIC) by ESA’s Next Generation Gravity Mission (NGGM), setting anticipation for higher spatial and temporal resolution of satellite gravity observations in the near future.

This contribution presents initial results of multi-decadal closed loop simulations of current and future satellite gravity observations, comparing their capabilities to allow a direct estimation of long-term trends in changes of TWS and ocean mass. The observed climate signal is based on components of the TWS, as well as mass change signals of oceans, ice sheets, and glaciers extracted from CMIP6 climate projection following the shared socio-economic pathway scenario. A special focus here is on the long-term trend over the oceans. By subtracting the observed ocean mass change from the overall sea level change, the global ocean heat content can be computed from the steric component of the sea-level rise. The resulting long-term trends are then compared to initial inputs to the simulation to illustrate the difference in performance between current and future satellite gravity constellations.

How to cite: Schlaak, M., Roland, P., Blazquez, A., Meyssignac, B., and Lemoine, J.-M.: Multi-decadal Satellite Gravity Mission Simulations Comparing Resolving Capabilities of a Long-term Trend in the Global Ocean Heat Content, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8590, https://doi.org/10.5194/egusphere-egu23-8590, 2023.

Terrestrial Water Storage (TWS) is a measure of the total amount of net-accumulated water in all continental storage compartments. The Global Climate Observing System programme (GCOS) has recently approved TWS Anomalies as an Essential Climate Variable (ECV). With GRACE and GRACE-FO we have the ability to look back on an observable that can be interpreted as monthly TWS change since the year 2002. In the continental water mass budget equation, this change balances the water fluxes from precipitation, evapotranspiration and runoff. 

Within the framework of the new Collaborative Research Cluster 1502 'DETECT', we analyse terrestrial/atmospheric and surface water fluxes and associated budget contributions from model simulations, reanalyses and remote sensing observations for all larger river basins in Europe and combine them with catchment-integrating TWS variability. While, as a first step, we are updating previous budget analyses with latest available data sets, the project's central objective is to quantify to what extent regional changes of land and water use contribute to observed budget changes.

In this presentation, we introduce our central objectives and show first results of the latest continuation of catchment-wide water mass flux time-series analysis over Europe. We discuss our budgeting strategies as well as opportunities and hurdles concerning data availability and uncertainties --- also in view of the recently launched SWOT mission and future GRACE successors.

How to cite: Gutknecht, B. D., Springer, A., and Kusche, J.: Water Mass Fluxes and Budgets at Catchment-Scale over Europe in the Collaborative Research Cluster 'DETECT', EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9933, https://doi.org/10.5194/egusphere-egu23-9933, 2023.

For 25 years, geodesists have inferred that the displacement of the "geocenter" estimated from (SLR) satellite laser ranging represents fluctuation of Earth's fluid envelope relative to solid Earth.  However, SLR determines the displacement of the (CN) center of network of geodetic sites relative to the (CM) center of mass of Earth, consisting of solid Earth, the oceans, the atmosphere, and continental water, snow, and ice. Because solid Earth's surface is deforming in elastic response to the changing load of continental water, atmosphere and oceans, CN only roughly approximates the (CE) center of mass of solid Earth.  In this study, estimate the velocity of CM relative to the (CE) center of mass of Earth by first correcting SLR site displacements (estimated by the International Laser Ranging Service 2020) for their elastic response relative to CE produced by fluctuations of continental water, atmosphere and oceans.  We maintain that by correcting for loading displacements relative to CE, we arrive at an estimate of the displacement of CE.  We find that transforming the SLR series from CN to CE reduces the discrepancy between the seasonal oscillation of Earth's fluid envelope estimated by SLR and that assumed by GRACE (using the technique of Sun et al. 2017) by 40 per cent.  In both SLR and GRACE, a total of 0.5 x 10¹⁶ kg of mass moves between hemispheres from southern oceans in August to snow-covered areas in North America and Europe (in particular in Canada and Siberia).  The primary remaining difference between the two techniques is that mass in the northern hemisphere is maximum on February 5 in SLR, 20 days before it is maximum on Feb 25 in GRACE.  Knowing the total transfer of the mass of between hemispheres places a boundary constraint on global models of circulation of water on land and in the oceans and atmospheres (that may be applied to forecasting extreme events such as flooding and drought).

How to cite: Argus, D., Landerer, F., Wiese, D., and Blewitt, G.: Resolving the discrepancy betweenthe seasonal oscillation of Earth's fluid envelope estimated with SLR and that assumed in GRACE, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10758, https://doi.org/10.5194/egusphere-egu23-10758, 2023.

An important application of the NASA/GFZ GRACE and GRACE-FO satellites is the derivation of ice mass changes in the arctic regions from the gravity field changes. Looking at climate change, it is important to know how fast the ice caps are melting for global sea level rise estimation and validation of climate models. We use recently released L2 GRACE/GRACE-FO models, including the latest CSR release 6.1, which show major improvement over earlier models, especially for Antarctica, as well as the latest TU Graz models.  We also compare the GRACE results to a new surface mass balance model, and joint high-resolution inversion with ESA’s Earth Explorer CryoSat altimetry data, highlighting areas of dynamic changes and giving a higher resolution on the main mass change areas. The study is a precursor to a project for demonstrating use of Level-1 laser data for glacial change detection.

How to cite: Jenny, B., Hansen, N., Jensen, T., and Forsberg, R.: Mass change of Antarctica from new GRACE/GRACE-FO releases, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12155, https://doi.org/10.5194/egusphere-egu23-12155, 2023.

Geophysical interpretation of polar motion (PM) and finding the sources of its excitation is an important but challenging task that takes place on the boundary between geodesy and geophysics. Especially the role of hydrological signals in PM excitation is not yet fully understood, mainly because of the lack of agreement between estimates of hydrological angular momentum (HAM) computed from different data sources (e.g., land surface models, global hydrological models, satellite gravity measurements).

The recently observed climate changes affect the global distribution and transport of continental water mass, which may also influence the HAM. Projections of past and future changes in the physical and chemical properties of the atmosphere, ocean, and hydrosphere caused by climate change are delivered by climate models, which are collected and made available to the public in the frame of the sixth phase of the Coupled Model Intercomparison Project (CMIP6). Such models provide many of variables, including variations in soil moisture and snow water storage, which are necessary for HAM computation. However, CMIP6 models differ in terms of initial conditions, physical properties of atmosphere, oceans, hydrosphere, and climate forcing. Such divergences obviously contribute to the differences between various CMIP6-based HAM series.

In this study, we investigate various groups of models according to providing institute, mean of selected models and more sophisticated combinations determined using different methods like e.g., variance components estimation, three cornered hat method. The obtained series are analyzed and evaluated in several spectral bands. The goal of such study is to check whether grouping or combining the models could improve the consistency between CMIP6-based HAM and hydrological signal in geodetically observed PM excitation. To evaluate the combined CMIP6-based HAM series, we compare them with geodetic residuals (GAO) obtained from geodetic angular momentum reduced by atmospheric and oceanic signals, as well as with HAM computed from data from Gravity Recovery and Climate Experiment (GRACE) mission. Generally, the analyses confirm the results obtained from previous studies (Nastula et al. 2022). It is possible to find grouped CMIP6 models that provide HAM series as or more compliant with GAO than HAM determined from GRACE.

How to cite: Nastula, J., Kur, T., Śliwińska, J., Wińska, M., and Partyka, A.: Study on combination approaches for hydrological angular momentum determined from climate data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12215, https://doi.org/10.5194/egusphere-egu23-12215, 2023.

We use the land-ice surface height data product (ATL06 release 5) from NASA’s latest satellite laser altimetry, the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) to compute surface elevation changes (SEC) from October 2018 to September 2021 over both Antarctica and Greenland. To convert the SEC to mass change we need to remove the non-ice related SEC processes. To remove the signal from the firn compaction, we use an offline surface energy and firn model. The model is driven by outputs from the atmospheric regional climate model HIRHAM5, forced with reanalysis dataset ERA5, and it simulates the physics of the firn pack. The vertical bedrock movement also creates non-ice related signals, the glacial isostatic adjustment has been computed using the ICE-7G model and SELEN4, and the elastic rebound has been computed using a modified version of the REAR code. 

When the SEC are corrected for signals that are not associated with a change in snow or ice mass, we convert to mass change by multiplying the height change with an appropriate density.  The corrected SEC can result from a change in either melt, snow accumulation, or dynamical behavior, this means that the appropriate density depends on which physical processes are driving the observed SEC. In this study, we have made a new density parametrization to convert the volume change into mass change. The density parametrization determines if one should multiply with snow densities (250-350 kg/m³) or ice density (917 kg/m³) based on a number of criteria; the sign of SEC, ice flow velocity, and the altitude of the area.
With our new density parametrization, we get that the Greenland Ice Sheet has lost 237.5±10.3 Gt/year and the grounded Antarctic Ice Sheet has lost -137.6±27.2 Gt/year in the period. These results are in agreement with other mass balance estimates derived with different methods.

How to cite: Hansen, N., Sørensen, L. S., Spada, G., Melini, D., Forsberg, R., Mottram, R., and Simonsen, S. B.: ICESat-2 Ice Sheet Mass balance: Going below the surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12349, https://doi.org/10.5194/egusphere-egu23-12349, 2023.

Time variable satellite gravimetry, realized with the missions GRACE and GRACE-FO, allows for the only global observation of total water storage (TWS) changes. These observations are inherently smoothed due to the upward continuation of the gravity field at the satellite orbits. Additionally, the correlated errors seen as north-south stripes in global maps require further filtering to separate signal from noise. This causes the signal at any region to be biased by signal at neighboring regions, better known as leakage effect. Various methods have been proposed to mitigate leakage and to spatially assign TWS changes at smaller spatial scales than the satellite data is available by using auxiliary information. Unfortunately, there is a large spatio-temporally variable degree of discrepancy in the agreement or the disagreement within these methods, leaving the non-geodetic users of GRACE TWS changes with the complex question of choosing an appropriate method. The scaling factor approach and the Data-Driven Correction (DDC) approach are the most widely used methods. The scaling factor approach uses a numerical model output of TWS changes, whereas the DDC approach uses only GRACE observations to account for leakage.
Tripathi et al., 2022 (10.5194/hess-26-4515-2022) found for the Indus basin, that a newly proposed variant of the scaling factor method, called Frequency-Dependent scaling, using the WaterGAP (Water Global Assessment and Prognosis) hydrology model (WGHM v2.2d), produced results with a striking agreement against the results from the DDC approach. Therefore, this contribution extends the comparison of Frequency-Dependent scaling using WGHM v2.2d against the DDC method for 189 global hydrological basins. We achieved an agreement between the results from both methods well within the uncertainties of GRACE TWS observations for almost 85-90% of the global hydrological basins. Such an agreement can bring a much-needed consolidation in the treatment of leakage effect across the user community. The disagreement in the rest of the basins varies across time scales, such as long-term trends and periodic signals, and is being further analysed.

How to cite: Tripathi, V., Vishwakarma, B. D., and Horwath, M.: Data-Driven and Scaling Factor methods of GRACE leakage correction: Can they be reconciled?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12485, https://doi.org/10.5194/egusphere-egu23-12485, 2023.

Accurate representation of the time-variable atmospheric state is achieved by assimilating numerous and disparse observations into numerical weather models (NWM). The four-dimensional atmospheric density distribution, a derivative of essential meteorological variables, affect among else how electromagnetic signals propagate through Earth’s atmosphere and how satellites orbit through Earth’s gravity field. Atmospheric refraction to which microwave signals are subjected as they traverse the electrically neutral atmosphere is quantified e.g., during the GNSS data analysis, and holds valuable information about the water vapor distribution in the vicinity of the ground stations. Satellite gravimetry as realized by the GRACE and GRACE-FO missions is sensitive to mass redistribution within Earth’s fluid envelope, including but not limited to the atmosphere and the terrestrail water storage, and also to high-frequency variations stemming from the time-integrated effect of precipitation and evapotranspiration. In this contribution we employ two state-of-the-art meso-beta scale NWM (ECMWF’s latest reanalysis ERA5 and DWD’s operational model ICON-global) as well as ERA5‘s ensemble members to demonstrate that tropospheric mosture distribution and net atmospheric freshwater fluxes are quite uncertain in modern NWM in comparison to other quantities such as hydrostatic atmospheric mass and that certain space geodetic observing systems such as GNSS and GRACE-FO are appropriate tools to monitor them, thus enhancing the accuracy of weather prediction.

How to cite: Balidakis, K., Dobslaw, H., Zus, F., Eicker, A., Dill, R., and Wickert, J.: Prospects of Space Geodesy to Monitor Atmospheric Moisture and Atmospheric Net-Water Fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13048, https://doi.org/10.5194/egusphere-egu23-13048, 2023.

In a warming climate, atmospheric water vapour will increase, intensifying the global water cycle. However, this ”wet-get-wetter” and ”dry-get-drier” paradigm does not hold on regional scales and models seem to contradict observations. Furthermore, it is unknown whether modelled atmospheric moisture fluxes, entering and leaving the watersheds, are mass consistent with river discharge and sinks and sources such as aquifers, soil layers and surface waters. Consequently, observational evidence of the changing water cycle components is crucial for scrutinizing models. It is also essential to assess climatic water cycle trends which have far reaching ecological and socio-economic consequences, through the occurrence of heat waves, flooding, forest fires and water availability.

In this contribution, we introduce a 5 year research project, which was recently funded through the Vidi talent scheme programme of the Dutch Research Council. We will explain how we plan to use satellite gravimetry, radar altimetry, in a joint inversion scheme, to estimate water fluxes in and out of the watersheds of the North Sea region, and those of the Greater Horn of Africa. Furthermore, we’ll show how regional sea level change and vertical land motion will be consistently accounted for in the proposed estimation scheme.

How to cite: Rietbroek, R., Karimi, S., and Shakya, A.: Unravelling watershed fluxes to detect emerging changes of the water balance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13524, https://doi.org/10.5194/egusphere-egu23-13524, 2023.

Hydro-climatic variables such as precipitation (P), evapotranspiration (ET), terrestrial water storage (TWS) or river discharge define the terrestrial water cycle at local and global scales. The robust detection and quantification of steady trends in these variables require analysing sufficiently long time series of observations. Yet, historical discharge records may suffer from long data gaps or simply be too short; different reanalyses or data-driven models of P and ET often show large discrepancies and the associated uncertainty is not systematically provided. Finally, TWS has been observed only since the launch of GRACE in 2002 and also suffers from dozens of missing epochs.

Here, we present a 3-step approach to consistently reconstruct the historical time series of TWS and discharge at the catchment scale. In the first step, we use in-situ discharge observations and TWS anomaly derived from GRACE(-FO) observations to identify a reduced-order and mass-conserving rainfall-discharge model of the catchment. In the second step, the model is run with different precipitation and evapotranspiration data sets to select the pair P and ET reproducing most accurately the observed discharge and TWS. If necessary, the resulting net water flux (P-ET) is adjusted with a bias to improve the simulation accuracy. lastly, we apply a Bayesian smoother such as the Rauch–Tung–Striebel smoother to estimate TWS and discharge along with their respective uncertainty over the period covered by the P-ET time series. Critical to the proposed approach is the rainfall-discharge model identification. Here, we assume that the observed monthly-averaged discharge at the outlet is primarily driven by the TWS in the upstream catchment. As a consequence, we first estimate a storage-discharge model in the form of a continuous-time differential equation. This equation is subsequently coupled with the water mass balance equation to form the rainfall-discharge model. Remarkably, this final model is estimated independently of any P and ET models.

Finally, we apply the proposed approach to Amazonian and Siberian catchments for a period spanning from 1980 to 2020. In the first case, linear and time-invariant models capture with reasonable accuracy the observed drainage dynamics. In contrast, non-linear or linear and time-variable models are necessary to take correctly into account the temperature-dependent snow and ice accumulation and thaw in the case of Siberian catchments.

How to cite: Douch, K., Saemian, P., and Sneeuw, N.: Reduced order rainfall-discharge model for hydro-climatic data assimilation: a data-driven approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15762, https://doi.org/10.5194/egusphere-egu23-15762, 2023.

In comparison with the number of tide gauges measuring in-situ sea-level change along the Northern Hermisphere coastlines, the Southern Hemisphere has a poor spatial distribution of stations. For example, along the South American Atlantic coastline, only 12 tide gauges are registered at the Permanent Service for Mean Sea-level (PSMSL), of which only two have been updated in the last three years. While satellite altimetry can be used to provide data in locations where there is no in-situ data, estimating coastal sea-level change using altimetry data is challenging due to the distortion of the satellite signal close to the land. Consequently, sea-level change along the South American Atlantic coastline is still poorly understood. Here, we fill this gap by using coastal altimetry products together with a new network of tide gauges deployed along the coast of Brazil (by the SIMCosta project). Via a sea-level budget analysis, we look at the regional drivers of sea-level change along the coast.

Recently, a large effort has been put towards developing algorithms that improve the accuracy of standard radar altimetry in coastal regions. Here, we compare both a coastal altimetry product (XTRACT/ALES) and a standard altimetry product (from CMEMS) to the local tide gauges. Previous studies have shown that, for some regions, coastal sea level is driven by open ocean sea-level change ( e.g., Dangendorf et al, 2021). Following this approach, we use clusters of coherent sea-level variability (Camargo et al., 2022), extracted with a network detection algorithm (delta-Maps), that extend to the open ocean, as proxies of the drivers of sea-level change along the coast.  The northern part of the study region, covering the Amazon Plateau, has a good match between the coastal altimetry-observed sea-level change and the sum of the drivers. The sum of the drivers and coastal altimetry trends also match, considering the uncertainty bars, for the most southern part, covering the Patagonian Shelf. For the other regions, we find a large difference between the coastal altimetry-observed sea-level change and the sum of the drivers. Thus, it is possible that these regions cover large-scale features, which are not strongly correlated with coastal sea level.

References

Camargo, C. M. L., Riva, R. E. M., Hermans, T. H. J., Schütt, E. M., Marcos, M., Hernandez-Carrasco, I., and Slangen, A. B. A.: Regionalizing the Sea-level Budget With Machine Learning Techniques, EGUsphere [preprint, accepted], https://doi.org/10.5194/egusphere-2022-876, 2022.

How to cite: M.L. Camargo, C., Gerkema, T., Okta Andrawina, Y., and B.A. Slangen, A.: Sea-level change along the South American Atlantic coastline, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16296, https://doi.org/10.5194/egusphere-egu23-16296, 2023.

The Earth Surface undergoes continuous deformation due to surface mass variations. These mass variations are primarily caused by the hydrological cycle, snowfall, ice melt and glacial isostatic adjustment (GIA). Modern geodetic sensing techniques like the Global Navigational Satellite System (GNSS) can sense these mass variations with unprecedented accuracy.  Therefore, the GNSS positioning time series provides a unique opportunity to study these mass variations and their causes.

In this study, we have used the GNSS time series from the region of Africa and Antarctica to analyse the mass variations. Conditions like draught and ice melting characterise these two regions. Therefore this current study will look at the signals of these two physical conditions. The results obtained are discussed and analysed.

How to cite: Ray, J. D., Patar, S., and Mahata, R.: Geodetic sensing of mass variations due to climatic conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16692, https://doi.org/10.5194/egusphere-egu23-16692, 2023.

Models of glacial isostatic adjustment (GIA) simulate the time-delayed viscoelastic response of the solid Earth to surface loading induced mainly by mass redistribution between ice and ocean during the last glacial cycle considering for rotational feedback, floating ice and moving coastlines. These models predict relative sea level change and surface deformation. The GIA component of present-day uplift is responsible for crustal uplift rates of more than 10 mm/year in areas such as Churchill (Canada) and Angermanland (Sweden). As GIA models have several uncertainties, the model output needs to be validated against observational data. Here, we validate displacements predicted by a GIA model code, VILMA-3D, by using space geodetically observed vertical land motion. We have created a GIA model ensemble using geodynamically constrained 3D Earth structures derived from seismic tomography to consider more realistic lateral variations in the GIA response. To validate the modelled uplift rates, we employ a multi-analysis-centre ensemble of GNSS station and geocentre motion coordinate solutions that have been assimilated into the latest international terrestrial reference frame (ITRF2020). Tectonic and weather signatures were reduced in estimating GNSS-derived velocities, and the trend signal is extracted from these GNSS time series with the STL method (seasonal-trend decomposition based on Loess).  Additionally, uplift rates observed within the ITRF2020 of VLBI, DORIS, and SLR are employed in this study. Because the geodetic stations are unevenly distributed, we employ a weighting scheme that involves the network density and the cross-correlation of the stations’ displacement time series. As measures of agreement for global and regional cases, we employ weighted root mean square error (RMSE) and weighted mean absolute error (MAE). With this validation, we determine the GIA model parameters that are most suitable for modelling present-day uplift rates and identify regions with the best and worst agreement.

The results show an agreement between RMSE and MAE for the global case (all stations are considered) and the majority of regional cases, except for the farfield (away from formerly glaciated regions) and for North America. For the global case and for separate regions covered by the major ice sheets during glaciation (North America, Fennoscandia, Antarctica, Greenland), the best fit is performed by the GIA models with 3D Earth structures which show largest lateral variability in viscosity. For the GIA model with the best global fit, the MAE ranges between 0.03 and 0.98 for the respective regions British Isles, Antarctica, farfield, Fennoscandia and North America. In contrast, for the three regions with the lowest amount of observational data, Patagonia, Alaska and Greenland, the MAE is increased to values between 2.07 and 8.63. In general, the MAE ranges between 0.83 and 0.78 for the different GIA models when all stations are considered. Both the RMSE and the MAE show a larger spread between the regions than between the considered GIA models indicating the relevance of also evaluating regional differences in the model performance.

How to cite: Bagge, M., Boergens, E., Balidakis, K., Klemann, V., and Dobslaw, H.: Validation of Modelled Uplift Rates with Space Geodetic Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3351, https://doi.org/10.5194/egusphere-egu23-3351, 2023.

Vertical land motion (VLM) is an important component in relative sea-level (RSL) projections, especially at regional to local scales and over the short to medium term. However, VLM is difficult to derive because of a lack of long-term instrumental records (e.g., GPS, tide gauge). Geological data offer an alternative, revealing RSL histories over thousands of years that can be compared with glacial isostatic adjustment (GIA) models to isolate VLM.

Here, we present a case study from the Oka estuary, northern Spain. We apply two GIA models for the Atlantic coast of Europe with different ice model inputs (ICE-6G_C and ANU-ICE) but the same 3D Earth model. Both models fit well with the late Holocene RSL data along the Atlantic coast of Europe, with misfit statistics < 1.5, except the Oka estuary region, where both models show notable misfits with misfit statistics > 4.5. The significant misfits of both models in the Oka estuary region are indicative of local subsidence. The nearby GPS (station SOPU) with 15 years records shows a VLM rate of -0.96 ± 0.57 mm/yr (subsiding) compared to -0.15 ± 0.40 mm/yr to -2.48 ± 0.37 mm/yr elsewhere along the Atlantic coast of Europe. The VLM rate of SOPU accounts for the misfit between the GIA models and late Holocene RSL data, which decreases by ~90% from > 4.5 to ~0.5 after the subsidence correction of the late Holocene RSL data. The VLM rate incorporated in IPCC AR6 projections in Oka estuary is ~0.18 mm/yr (uplifting), which is contradictory in direction. Therefore, the projected sea-level rise rate is underestimated by 19 - 25% by 2030, 14 - 20% by 2050 and 9 - 26% by 2100 under the five Shared Socioeconomic Pathway (SSP) scenarios (SSP1-1.9, SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). Our study indicates the importance of considering local/regional VLM component in sea-level projections.

How to cite: Li, T., García-Artola, A., Walker, J., Cearreta, A., and Horton, B.: The importance of underestimated local vertical land motion component in sea-level projections: A case study from the Oka estuary, northern Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4604, https://doi.org/10.5194/egusphere-egu23-4604, 2023.

The Antarctic Ice Sheet (AIS) is the largest ice sheet on Earth that has known important mass changes during the last 26 kyrs. These changes deform the Earth and modify its gravity field, a process known as Glacial Isostatic Adjustment (GIA). GIA is directly influenced by the mechanical properties and internal structure of the Earth and is monitored using Global Navigation Satellite System positioning or gravity measurements. However, GIA in Antarctica remains poorly constrained due to the cumulative effect of past and present ice-mass changes, the unknown history of the past ice-mass change, and the uncertainties of the mechanical properties of the Earth. The viscous deformation due to GIA is usually modeled using a Maxwell rheology. However, other geophysical processes employ the Andrade rheology for tidal deformation or Burgers for post-seismic deformation which could result in a more rapid response of the Earth. We investigate the effect of using these different rheologies to model GIA-induced deformation in Antarctica.
We use the Love number and Green functions formalism to compute the radial surface displacements and the gravity changes induced by the past and present day ice-mass changes. We use the elastic properties and the radial structure of the Preliminary Reference Earth Model (PREM) and the viscosity profile VM5a given by Peltier et al., 2015 and a modified version of it to account for the recent results published regarding the present-day ice-mass changes. Deformations are computed for each rheological laws mentioned above using ICE6g deglaciation model and altimetry data from various satellite missions over the period 2002 to 2017 to represent the past and present changes of the AIS, respectively.
We find that the three rheological laws lead to significant discrepancies in the Earth response. The differences are the largest between Maxwell and Burgers rheologies during the 100 -1000 years following the beginning of the surface-mass change. First using a simple deglaciation model, we find that the deformations rates can be 3 times and 1.5 times greater using the Burgers and Andrade rheologies. However, the ratio between the gravity change rate and the displacement rate are similar for all rheologies (less than 5% difference). Results show that using the Andrade and Burgers rheologies can lead to a 5 and 10m difference in the radial displacement with regards to the Maxwell rheology, on a 200 year period after deglaciation using the ICE6g model. Regarding the response to present changes in Antarctica, the largest discrepancies are obtained in regions with the greatest current melting rates, namely Thwaites and Pine Island Glacier in West Antarctica. Using the Burgers and Andrade rheologies lead to deformations rates respectively 6 times and 2 times greater with respect to Maxwell rheology.

How to cite: boughanemi, A. and mémin, A.: Study of the impact of rheologies on GIA modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6911, https://doi.org/10.5194/egusphere-egu23-6911, 2023.

At present, exploring the space of rheological parameters in models of glacial isostatic adjustment (GIA) and relative sea level (RSL) which incorporate laterally variable Earth structure is computationally expensive. A single simulation using the Seakon model (Latychev et al., 2005), using contemporary high-performance computing hardware, requires several wall-days & ≈ 1 core-year for one RSL simulation from late Marine Isotope Stage 3 to present day. However, it is well established that the impact from laterally variable mantle viscosity and lithospheric thickness on RSL and GIA is significant (Whitehouse, 2018). We present initial results from using the Tensorflow (Abadi et al.) framework to construct artificial neural networks that emulate the difference in the rate of change of relative sea level and relative radial displacement between model configurations using spherically symmetric (SS) and laterally variable (LV) Earth structures. Using this emulator we can accurately sample the parameter space (≈ 360 realisations of the background (SS) structure) for a given realization of lateral Earth structure (e.g. viscosity variations derived from shear-wave tomographic models) using ≈ 1/10th the amount of parameter vectors as a training set. Average misfits are O(0.1-1%) of the total RSL signal when using the emulator to adjust SS GIA model output to incorporate the impact from LV. We shall report on two case studies which allow us to examine the influence of lateral Earth structure on inferences of background (i.e. global-mean) viscosity. For these case studies, the emulator, in conjunction with a fast SS GIA/RSL model, is used to determine optimal Earth model parameters (elastic lithosphere thickness, upper and lower mantle viscosities) by calculating the model misfits across the parameter space. The first case study uses the regional RSL database of Vacchi et al. (2018) which spans the Canadian Arctic and East Coast with several hundred sea level index points and limiting points for the early to late Holocene. The second case study uses a global database of several thousand contemporary uplift rates derived from GPS data (Schumacher et al., 2018). For the first case study we find two main features from incorporating LV structures compared to the SS configuration: a decrease in the best scoring misfit and a shift of the misfit distribution in the parameter space to favour a reduced upper mantle viscosity and reduced sensitivity to the lower mantle viscosity.

References
Abadi, M., Agarwal, A., Barham, P., et al.: TensorFlow: Large-Scale Machine Learning on Heterogeneous Systems, https://www.tensorflow. org/.
Latychev, K., Mitrovica, J. X., Tromp, J., et al.: Glacial isostatic adjustment on 3-D Earth models: a finite-volume formulation, GJI, 161, 421–444, https://doi.org/10.1111/j.1365-246x.2005.02536.x, 2005.
Schumacher, M., King, M. A., Rougier, J., et al.: A new global GPS data set for testing and improving modelled GIA uplift rates, GJI, 214, 2164–2176, https://doi.org/10.1093/gji/ggy235, 2018.
Vacchi, M., Engelhart, S. E., Nikitina, D., et al.: Postglacial relative sea-level histories along the eastern Canadian coastline, QSR, 201, 124–146, https://doi.org/10.1016/j.quascirev.2018.09.043, 2018.
Whitehouse, P. L.: Glacial isostatic adjustment modelling: historical perspectives, recent advances, and future directions, Earth Surface Dynamics, 6, 401–429, https://doi.org/10.5194/esurf-6-401-2018, 2018.

How to cite: Love, R., Ajourlou, P., Parang, S., Milne, G. A., Tarasov, L., and Latychev, K.: Emulating the influence of laterally variable Earth structure in a model of glacial isostatic adjustment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7921, https://doi.org/10.5194/egusphere-egu23-7921, 2023.

Ice mass loss from the Greenland Ice Sheet and Arctic glaciers has accelerated over the last three decades due to rapid changes in Arctic climate. This loss of ice from glaciated areas and redistribution of water across the global oceans creates a complex spatio-temporal pattern of crustal deformation due to the load changes on Earth’s surface. We test whether the resulting strain perturbations from this deformation are large enough to influence seismic activity in the Arctic on decade to century timescales.

Using new ice-mass-loss estimates from radar altimetry for the Greenland Ice Sheet and model reconstructions of glaciers across the European Arctic, we predict gravitationally self-consistent sea level changes across the Arctic over the last three decades. These surface loads are then used as input for our deformation model, developed to calculate strain at depth within the crust, using a Love number formulation for a spherically symmetric Earth. Our global model captures both the near-field effects directly beneath ice centers and deformation across the sea floor, allowing us to fully quantify the spatio-temporal perturbations to the regional strain field created by glacial isostatic adjustment (GIA) processes. Using declustered earthquake catalogs of Arctic earthquake activity over the last three decades, we search for correlation between the earthquake record and our modelled strain perturbations. In particular, we focus our search along the Mid Atlantic Ridge and beneath Greenland. In the former, small magnitude GIA-related strains enhance or counteract rapid tectonic background loading, while in the latter intra-plate setting, GIA processes likely dominate the crustal strain field.

While correlations over the last three decades may not be statistically definitive, this framework also allows for prediction of crustal strain patterns for future ice sheet scenarios, as ice mass loss from Greenland accelerates, and therefore predictions of the likelihood and potential geographic variability of climate-change-induced seismicity in the future.

How to cite: Coulson, S., Hoffman, M., Dascher-Cousineau, K., Delbridge, B., Bürgmann, R., and Carmichael, J.: Quantifying the Impact of Modern Ice Mass Loss on Crustal Strain and Seismicity across Greenland and the European Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9405, https://doi.org/10.5194/egusphere-egu23-9405, 2023.

In this study, we examine the relationships among mantle viscosity, ice models and RSL data. We analyzed two widely used ice models, the ANU and ICE-6G ice models, and found significant difference between these two models, suggesting that significant uncertainties exist in ice models. For six RSL datasets covered both the near- and far-field from published works [Peltier et al., 2015; Lambeck et al., 2014, 2017; Vacchi et al., 2018; Engelhart et al., 2012, 2015], we performed forward GIA modelling using a 1-D compressible Earth model to seek the preferred upper and lower mantle viscosities that fit each of the six RSL datasets, for each of these two ice models. Our calculations show that viscosity in the lower mantle is significantly larger than the upper mantle for almost all the pairs of RSL datasets and ice models, but the RSL datasets for North America and Fennoscandia by Peltier et al., [2015] can be matched similarly well with a large parameter space of upper and lower mantle viscosities, both relatively uniform mantle viscosity and with large increase with depth. The preferred mantle viscosity using the ANU ice model and Lambeck et al. [2017] RSL data for North America is in a good agreement with that by Lambeck et al. [2017].    By using the GIA model with the preferred viscosity structures, we constructed the spatial and temporal distributions of misfit to different RSL datasets, for both the ICE-6G and ANU ice models. The misfit patterns for the ANU and ICE-6G ice models do not differ significantly in North America, although these two ice models differ greatly in North America. However, due to relatively small ice volume in ICE-6G, it fails to explain the far-field RSL data, reflecting the so-called “missing ice” problem. Guided by the spatial and temporal misfit patterns, we made initial attempts to modify ICE-6G by adding more ice to the ice model to improve the fit to far-field RSL data. The three modified ICE-6G ice models we consider all significantly improve far-field RSL data, while maintaining or even improving misfit for near field RSL data. This shows the promise with our method in improving ice models and fit to RSL data.

How to cite: Kang, K. and Zhong, S.: Constraints of Relative Sea Level Change on the Late Pleistocene Deglaciation History, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9697, https://doi.org/10.5194/egusphere-egu23-9697, 2023.

Twelve continuous GNSS systems are deployed on bedrock across the Amundsen Embayment region, spanning the Pine Island, Thwaites and Pope-Smith-Kohler (PSK) glacial drainage network of the West Antarctic Ice Sheet.  Continuous daily position time series for these sites range from 4 to 12 years, yielding reliable crustal motion velocity solutions at these fast-moving bedrock sites. Remarkably, multiple stations record sustained uplift of 40-50 mm/yr.  Maximum uplift defined by the current distribution of sites is centered on the Pope-Smith-Kohler glaciers, where rapid thinning and grounding line retreat is well documented. Horizontal bedrock displacements, which are particularly sensitive to the location of changing surface mass loads, show a clear radial pattern with motion outward away from upstream portions of the Pope/Smith glaciers. Several modeling studies suggest there is a viscous deformation response to this decadal mass loss. Our modeling, however, shows that elastic deformation response explains nearly the entire measured signal at the PSK region sites. We will present new modeling results and discuss implications for ongoing cryosphere-solid Earth interactions.

How to cite: Wilson, T., Gómez, D., Matheny, P., Bevis, M., Durkin, W. J., Kendrick, E., Konfal, S., and Saddler, D.: New GNSS Observations of Crustal Deformation due to Ice Mass Loss in the Amundsen Sea Region, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10493, https://doi.org/10.5194/egusphere-egu23-10493, 2023.

We present the Antarctic and Greenland components of an extensive
history matching for last glacial cycle evolution and regional earth
rheology from glaciological modelling with fully coupled regional
visco-elastic glacio-isostatic adjustment.  Of further distinction is
the accounting for model structural uncertainty. The product is a high
variance set of joint chronologies and earth model parameter vectors
that are not inconsistent with available constraints given
observational and model uncertainties.

Ensemble parameters are from Markov Chain Monte Carlo sampling with
Bayesian artificial neural network emulators.  The glaciological model
is the Glacial Systems Model with hybrid shallow shelf and shallow ice
physics and a coupled energy balance climate model. It includes a much
larger set of ensemble parameters (34 and 38 respectively for
Greenland and Antarctica) than other paleo ice sheet models to
facilitate more complete assessment of past ice sheet evolution
uncertainty. The history matching is against a large curated set of
relative sealevel, vertical velocity, cosmogenic age, and marine
constraints as well as the present-day physical and thermal
configuration of the ice sheet.

The careful assessment of uncertainties, breadth of modelled
processes, and sampling approach has resulted in NROY (not ruled out
yet) chronologies and rheological inferences that contradict previous
more limited model-based reconstructions.  For instance, in contrast
to most previous inferences for the Antarctic contribution to the last
glacial maximum (LGM) low-stand (with inferred values of about 10 m ice
equivalent sea-level (mESL), our NROY set includes chronologies with
LGM contributions of up to 23 mESL.  This result represents a
potentially significant contribution towards addressing the challenge
of LGM missing ice.

How to cite: Tarasov, L., Lecavalier, B., Balco, G., Hillenbrand, C.-D., Milne, G., Roberts, D., and Woodroffe, S.: GLAC3: Joint glaciological model and visco-elastic earth model history matching of the last glacial cycle: Greenland and Antarctica components, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10574, https://doi.org/10.5194/egusphere-egu23-10574, 2023.

ANET-POLENET (Antarctic Network of the Polar Earth Observing Network) bedrock GNSS sites in the Ross Sea region of Antarctica surround an LGM load center in the Siple region of the Ross Embayment and record crustal motion due to GIA.  Rather than a radial pattern of horizontal motion away from the former load, we instead observe three primary patterns of deformation; 1) motions are reversed towards the load in the southern region of the Transantarctic Mountains (TAM), 2) motions are radially away from the load in the Marie Byrd Land (MBL) region, and 3) an overall gradient in motion is present, with magnitudes progressively increasing from East to West Antarctica.  We investigate the effects of alternative Earth model and ice loading scenarios, with the goal of understanding these distinct patterns of horizontal bedrock motion and their drivers. Using GIA models with a range of 1D Earth models, alternative ice loading scenarios for the Wilkes Subglacial Basin (LGM time scale) and the Siple Coast (centennial and millennial time scales) are explored.  We find that no 1D model, regardless of the Earth model and ice loading scenario used, reproduces all three distinct patterns of observed motion at the same time.  For select ice loading scenarios we also examine the influence of more complex rheology by invoking a boundary in Earth properties beneath the Transantarctic Mountains.  This approach accounts for the strong lateral gradient in Earth properties across the continent by effectively separating East and West Antarctica into two different Earth model profiles.  Some of our GIA models utilizing 3D Earth structure reproduce predicted motions that match all three observed patterns of deformation, and we find that a multiple order magnitude of change in upper mantle viscosity between East and West Antarctica is required to fit the observations. 

How to cite: Konfal, S., Wilson, T., Whitehouse, P., Nield, G., Hermans, T., van der Wal, W., Bevis, M., Gómez, D., and Kendrick, E.: Observations and modelling of GIA in the Ross Sea region, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10729, https://doi.org/10.5194/egusphere-egu23-10729, 2023.

Glacial isostatic adjustment (GIA) represents an important negative feedback on ice-sheet dynamics. The magnitude and time scale of GIA primarily depend on the upper mantle viscosity and the lithosphere thickness. These parameters have been found to vary strongly over the Antarctic continent, showing ranges of 10¹⁸ - 10²³ Pa s for the viscosity and 30 - 250 km for the lithospheric thickness. Recent studies show that coupling ice-sheet models to 3D GIA models capturing these spatial dependencies results in substantial differences in the evolution of the Antarctic Ice Sheet compared to the use of 1D GIA models, where the solid-Earth parameters are assumed to depend on the latitude but not on the longitude and the depth. However, 3D GIA models are computationally expensive and sometimes require an iterative coupling for the ice sheet and the solid-Earth solutions to converge. As a consequence, their use remains limited, potentially leading to errors in the simulated ice-sheet response and associated sea-level rise projections. Here, we propose to tackle this problem by generalising the Fourier collocation method for solving GIA proposed by Lingle and Clark (1985) and implemented by Bueler et al. (2007). The method allows for an explicit accounting of the effects of spatially heterogeneous viscosity and lithospheric thicknesses and is computationally very efficient. Thus, for a continental domain at relatively high spatial resolution (256 x 256 grid points) and a 1-year time step, the model runs with speeds of ca. 200 simulation years per second on a single CPU, while keeping the error low compared to 3D GIA models. As the time step is small enough, the need of an iterative coupling method is avoided, thus making the model easy to couple with ice-sheet models.

How to cite: Swierczek-Jereczek, J., Montoya, M., Blasco, J., Alvarez-Solas, J., and Robinson, A.: A generalised Fourier collocation for fast computation of glacial isostatic adjustment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13583, https://doi.org/10.5194/egusphere-egu23-13583, 2023.

Recent studies have shown that in the area of the Kangerlussuaq glacier, a large GPS velocities residual after removing predicted purely elastic deformations caused by present-day ice loss suggests the possibility of a fast rebound to little ice age (LIA) deglaciation. We previously investigated this area with a Maxwell viscoelastic rheology Earth model and compared the model predictions with GPS residual. We found a match for a rather thick lithospheric thickness and a rather low mantle viscosity structure beneath SE-Greenland. In this study we are going to examine the effect of a Burger model: 1) we compare the results with those from the Maxwell model and 2) we estimate if and where the differences can be discriminated with observational data.
Maxwell models describe a steady state mantle deformation and they are the most commonly model used in post glacial rebound problems. Burgers models, instead, describe a time-varying mantle deformation, which include an initial fast transient components followed by a steady-state phase of mantle deformation. This kind of transient deformation would allow to reconcile the Earth rebound caused by the Pleistocene deglaciation and the faster rebound caused by the recent LIA deglaciation.
We then analyze several scenarios of ice retreat in the last 2000 years in the fiord in front of Kangerlussuaq glacier, in view of the difference between the two rheologies.

How to cite: Barletta, V. R., Bordoni, A., and Khan, S. A.: Effect of transient deformation in southeast Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14958, https://doi.org/10.5194/egusphere-egu23-14958, 2023.

Fennoscandia is continuously uplifting in response to past deglaciation, a process known as glacial isostatic adjustment or GIA. One of the factors that controls the uplift rates is the viscosity of the upper mantle, which is difficult to constrain. Here, we reconstruct the upper mantle viscosity structure of Fennoscandia by inferring temperature and water content from seismic and magnetotelluric (MT) data. Using a 1-D MT model for Fennoscandian cratons together with a global seismic model, we infer an upper mantle viscosity range of ~10¹⁹ - 10²⁴ Pa·s for 1 – 10 mm grain size, which encompasses the GIA-constrained viscosities of 10²⁰ - 10²¹ Pa·s. The associated viscosity uncertainties of our calculation are attributed to the uncertainties associated with the geophysical data and unknown grain size. We can obtain tighter constraints if we assume that the Fennoscandian upper mantle is either a wet harzburgite (10^19.2 - 10^23.5 Pa·s) or a dry pyrolite (10^20.0 - 10^23.6 Pa·s) below 250 km, where pyrolite is ~10 times more viscous than harzburgite. Furthermore, assuming a constant grain size of either 1 mm or 10 mm reduces the viscosity range by approximately 2 orders of magnitude. In northwestern Fennoscandia, where a high-resolution 2-D resistivity model is available, the calculated viscosities are ~10 - 100  times lower than those for the Fennoscandian craton because the mantle has a higher water content, and both pyrolite and harzburgite must be wet. Overall, our calculated viscosities for Fennoscandia that are constrained from seismic and MT observations agree with the mantle viscosities constrained from GIA. This suggests that geophysical observations can usefully constrain upper mantle viscosity, and its lateral variations, for other parts of the world without GIA constraints.

How to cite: Ramirez, F., Selway, K., Conrad, C., Smirnov, M., and Maupin, V.: Lateral and radial viscosity variations beneath Fennoscandia inferred from seismic and MT observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15597, https://doi.org/10.5194/egusphere-egu23-15597, 2023.

The existence and nature of Quaternary glaciations of the eastern part of the Arctic basin is very far from being solved, and many think glaciations there may been absent or very local, even at the Last Glacial Maximum.  It is unlikely under the conditions of permafrost and low precipitation during MIS 2, that the glaciers would have produced significant topographic relief.  However, significant ice loads will produce a significant isostatic response.  In the area of the Novosibirsk Islands, Holocene changes in sea level and transitions from continental to marine sedimentation indicate differences in emergence over the course of the transgression  that suggest the melting of significant grounded ice masses (e.g. Anisimov et al., 2009). Shorelines deviate from those expected from the hydroisostatic component. The best-fit isostatic model suggests significant LGM ice accumulation close to the ocean in the area of the Henrietta and Jeannette islands of the De Long archipelago in the East Siberian Sea. The uplift deviations in the Zhokhov island district are best matched for an effective elastic lithosphere thickness Te ~40 km. The ice accumulations close to the shelf-ocean margin in the last glaciation seem to also have occurred in earlier glaciations of the region.

Anisimov, M.A., Ivanova, V.V., Pushina, Z.V., Pitulko, V.V. 2009. Lagoon deposits of Zhokhov Island: age, conditions of formation and significance for paleogeographic reconstructions of the Novosibirsk Islands region // Izvestiya RAS, Geographical Series. No. 5. pp. 107-119.

How to cite: Amantov, A., Amantova, M., Cathles, L., and Fjeldskaar, W.: Glaciations of the East Siberian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17095, https://doi.org/10.5194/egusphere-egu23-17095, 2023.

Changes in Antarctic ice mass have been observed as gravity changes by the Gravity Recovery and Climate Experiment (GRACE) satellites. The gravity signal includes both the component of the ice mass change and the component of the solid Earth response to surface mass change (Glacial Isostatic Adjustment, GIA). Therefore, estimates of the ice mass change from GRACE data require subtraction of the gravity rates predicted by the GIA model (GIA correction).

Antarctica is characterized by lateral heterogeneity in seismic velocity structure. West Antarctica shows relatively low seismic velocities, suggesting low viscosity regions in the upper mantle. On the other hand, East Antarctica shows relatively high seismic velocities, suggesting a thick lithosphere. Here we investigate the dependence of the GIA correction on lithospheric thickness and upper mantle viscosity.

The GIA correction for the average viscoelastic structure of West Antarctica is nearly identical to that for the average viscoelastic structure of East Antarctica. There is a trade-off between the lithospheric thickness and the upper mantle viscosity. This trade-off may reduce the effect of the lateral variations in the Earth’s viscoelastic structure beneath Antarctica on estimates of Antarctic ice mass change.

How to cite: Irie, Y. and Okuno, J.: Sensitivity of Antarctic GIA correction for GRACE data to viscoelastic Earth structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17255, https://doi.org/10.5194/egusphere-egu23-17255, 2023.

The GRACE (Gravity Recovery and Climate Experiment) satellites measure the Earth’s geopotential, and we can use this data to monitor spatiotemporal mass load changes in Earth's ice sheets. The geopotential measurements are both resolution-limited by the orbital configurations and subject to the complexities of present-day sea level change; for example, when an ice sheet melts, the accompanying migration of water should lead to a systematic bias in GRACE estimates of ice mass loss (Sterenborg et al., 2013). Indeed, using mascons and an iterative approach, Sutterley et al. (2020) found that variations in regional sea level affect ice sheet mass balance estimates in Greenland and in Antarctica by approximately 5%. Here, we use the sea level equation in our inferences of ice-mass loss both to increase the resolution of those inferences and to include the sea-level response in the analysis of GRACE data. We will test the resolution, implementation, accuracy, and impacts of a constrained least squares inversion of GRACE data. We will then investigate how deformation associated with our estimates of ongoing global surface mass change affects Earth-model inferences from geodetic data and Glacial Isostatic Adjustment modeling, with a focus region of Fennoscandia.

How to cite: Powell, E. and Davis, J.: Using the sea level equation to increase the resolution of GRACE inferences: Implications for studies of Fennoscandian GIA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17418, https://doi.org/10.5194/egusphere-egu23-17418, 2023.

Since the times of Doodson it has been established that a record of length T is required to resolve tidal harmonics with a frequency separation 1/T. This rule, known as Rayleigh criterion, does not consider the actual resolution provided by the signal-to-noise ratio of the data. Available tidal analysis software, like Eterna, seek gravimetric parameters for a priori defined groups (sums) of harmonics that are assumed otherwise indistinguishable. The residual between the predicted tidal signal for groups and the recording is minimized with simple least squares (LS) fit.

We developed the new software, RATA, that abandons the concept of groups, so each tidal harmonic present in the catalogue receives its set of tidal parameters that are free to vary. The resulting ill-conditioned matrix is stabilized by Tikhonov regularization (ridge regression) in the LS objective function. To validate the results, we used the moving window analysis (MWA) technique for a priori groups, with the resulting local response model as the a priori model. Compared to the standard approach, which used the Wahr-Dehant-Zschau elastic analysis model, we clearly see that bias and beating patterns are significantly smaller or almost vanish. Hence, the local response model can capture the apparent temporal variations by appropriate tidal parameters within the MWA groups.

While the most information in each group is carried by the tidal wave with the largest amplitude, influence of other harmonics must be properly considered in estimated amplitudes and phases. Therefore, if amplification factor or phase from any other large amplitude harmonic in the group is significantly different from the expectation, the grouping parametrization might lead to an inaccurate (biased) estimate of tidal parameters. The trade-off parameter between data residuals and the model difference to the reference model is chosen at the corner of the misfit curve, indicating expected level of noise in the data. The resulting model parameters indicate “data-driven” groups to be inferred from significant harmonics in the inversion. To demonstrate the method and how it may be used to reveal system properties hidden by wave grouping, we analyzed 11.5 years gravity recordings from the superconducting gravimeter SG056 at the BFO (Black Forest Observatory, Schiltach). As a result, we distinguished 61 significant groups of harmonics for the local tidal response model, with no clear evidence that more groups are resolvable. Some of them highly violate Rayleigh criterion.

How to cite: Ciesielski, A., Forbriger, T., Zürn, W., and Rietbrock, A.: Regularization Approach to Tidal Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-825, https://doi.org/10.5194/egusphere-egu23-825, 2023.

Ocean tide models are created for a variety of applications ranging from serving as an altimetry correction to being applied as numerical model boundary forcings. DGFI-TUM’s Empirical Ocean Tide (EOT) and NASA's Goddard Ocean Tide (GOT) models are derived based on sea-level anomalies (SLA) from multi-mission satellite altimetry. All SLA measurements are corrected for geophysical effects, which means that the estimations of tides are reliant on the accuracy of these respective correction models. Within these corrections, tidal signals or frequencies that align closely with those of tides may be present which have clear downstream implications on the derivation of ocean tides from along-track satellite altimetry. 

In this study, the two different ocean tide models have been used as they utilise different techniques for tidal estimations but both are dependent on the chosen altimetric corrections. In the global EOT20 model, altimetric corrections played an important role in improving the accuracy of the model in the coastal region. However, these coastal optimised corrections may be influencing the open ocean performance of the model. This has meant that further investigations should take place to describe the best set of altimetry corrections to optimise the accuracy of tide estimations made by the EOT model in all regions. Additionally, several versions of the GOT model have been developed to contrast the influences of the different corrections both for the open ocean and coastal regions. 

In this presentation, the impact of different geophysical corrections (e.g. ionospheric, internal tide and mesoscale) are presented with the aim to conclude on the optimal set-up of these corrections for empirical tide models. Results here are shown in different experiments that include assessing the impacts of ocean tide estimations on both along-track as well as modelled estimations.

How to cite: Hart-Davis, M., Ray, R., Bordas Diaz, L., Schwatke, C., Dettmering, D., and Seitz, F.: Towards the optimisation of altimetry corrections for improved ocean tide modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1260, https://doi.org/10.5194/egusphere-egu23-1260, 2023.

With the continued rise in global mean sea level, accurate operational predictions of tidal height and total water levels have become crucial for early warning of potential extreme events in the coastal region. Ocean tides play an important role in extreme sea level events, with high oceanic tides increasing the likelihood of coastal flooding. The Dutch Continental Shelf Model in Flexible Mesh (DCSM-FM) is developed at Deltares to operationally estimate the total water levels to help trigger early warning systems to combat these extreme events along the Dutch coastline. At the boundaries of this model, a tidal forcing is applied from global ocean tide models to better incorporate the ocean tidal height estimations within the model.

In this study, a regional Empirical Ocean Tide model for the Northwest European Continental Sea (EOT-NECS) is developed with the aim to apply better tidal forcing along the boundary of the regional DCSM-FM. EOT-NECS is developed at DGFI-TUM by using thirty years of multi-mission along-track satellite altimetry to derive tidal constituents which are estimated both empirically and semi-empirically. Compared to the previous global iteration, EOT20, EOT-NECS showed a reduction in the root-square-sum error for the eight major tidal constituents of 0.525 cm compared to in-situ tide gauges.

Water levels of DCSM-FM are forced from a number of sources. At the open model boundaries, a combination of water levels from multiple global tide models, an estimation of the surge levels through an Inverse Barometer Correction based on the local atmospheric pressure, and the forcing of the density driven mean sea surface height from a global ocean recirculation model is used. A part of the water level signal is generated within the model domain. This is based on tidal potential within the model domain, meteorological forcing and baroclinic processes. In the 2D depth-averaged version of the model, the contribution of the latter is forced through a static water level field from the 3D version of the model, representing the Mean Dynamic Topography.

When applying constituents from EOT-NECS at the boundaries of DCSM-FM, an overall improvement of 0.42 cm was seen in the root-mean-square error of tidal height estimations made by DCSM-FM, with some regions exceeding a 1 cm improvement. The results demonstrate that there is a large importance in using the appropriate tide model(s) as boundary forcings and in this manuscript, the use of EOT-NECS has a clear positive impact on the total water level estimations made in the northwest European continental seas.

How to cite: Laan, S., Hart-Davis, M., Schwatke, C., Backeberg, B., Dettmering, D., Zijl, F., Verlaan, M., and Seitz, F.: European altimetry-derived tide model for improved tide and water level forecasting along the Dutch Continental Shelf, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1786, https://doi.org/10.5194/egusphere-egu23-1786, 2023.

The German Federal Maritime and Hydrographic Agency (BSH) operates the Tidal Information Service that is responsible for producing and publishing tidal predictions for German waters. Traditionally, the predictions are produced for tide gauge locations, which are situated almost exclusively at or close to the coastline. Water level observations from the tide gauges are used as input data for the respective tidal analyses. BSH strives to extend these point-wise predictions to an area-wide data set for the German Bight based on simulated water levels. This shall serve the increasing demands in the context of research, shipping and offshore activities. High quality area-wide tidal data might also be usable for the reduction of measurements from satellite altimetry in this region.

We present tidal analyses based on simulated water levels using the hydrodynamic-numerical model HBM. This model runs operationally at BSH. Many grid points that cover the Wadden Sea run dry around low water and require special attention in the analyses. Tidal parameters, such has the mean lunitidal intervals and tidal ranges, are compared with data from tide gauges. One challenge is the harmonisation of tidal predictions based on model data with those based on tide gauge observations, in order to produce consistent products. The results from this work could also help to improve the implementation of tides in HBM in the future.

How to cite: Boesch, A.: Towards area-wide operational tide predictions for the German Bight, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1886, https://doi.org/10.5194/egusphere-egu23-1886, 2023.

Recent numerical tidal modelling efforts strongly suggest that present day tides are anomalously large in comparison to the tides over the past 1.5 Gyr. Whilst these results can be qualitatively explained from dynamical principles, there are only a few quantitative validations of deep-time tidal simulations done using tidal proxies. One reason for this is a lack of easily accessible proxies for tides and something we are proposing to rectify here. Through extensive literature searches, we have identified over 600 publications containing potential tidal proxies and processed around 300 of them to date.

From the literature, we have identified proxies for three tidal properties. Under favourable circumstances, the geological record can provide direct estimates of the tidal range. These situations are rare (~10 papers have this information to date), but it is the best proxy for validation purposes. Tidal currents can be constrained by indirect methods. The presence of black shales indicates a poorly ventilated water column, which in turn is a sign of weak tides. By plotting the location of tidal mixing fronts and ensuring that they are located so black shales end on the stratified side of the front, we have a potential proxy for large-scale tidal current speeds. Tidal currents can also be constrained locally by investigating the dimensions of current ripples in the sediments. Finally, day-length, which is directly linked to global tidal dissipation rates, can often be inferred from the variation and cyclicity in layer composition and thickness in tidalites. These are vertically accreted laminated facies of a succession of couplets composed of sand and clay or silt and clay, with thicknesses of millimeters to centimeters, and they are at the heart of our inventory. Further potential proxies involve using paleobiology to track ranges of intertidal species (to obtain tidal ranges) and use microfossil assemblages as another mean of tracking tidal mixing from (and hence constrain current speed). As a proof-of-concept application, we revisit tidal model simulations from five deep-time slices showing that the methods we propose are viable as tidal proxies. The model simulations and proxies usually agree within the uncertainties of both methods.

The database will be made available to the community once the information currently in it has been quality controlled and used in our initial publications. Furthermore, any information that may be of use is welcome and we would love to hear about any potential tidal proxies you may have.

How to cite: Perez, I., Green, J. A. M., Bulawa, J., Ewing, A., Fitzgerald, L. A. M., Hewitt, J. M., and Pampaloni, O.: The tidal proxy database: development, application, and a call for help, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3227, https://doi.org/10.5194/egusphere-egu23-3227, 2023.

The ocean tides are a key driver of a range of Earth system processes. Tidal energy drives vertical mixing with consequences for ocean circulation, climate, and biological production, and the tidal stream transport sediments, pollutants, and other matter through the ocean. On long time-scales tidal drag acts to slow down Earth’s spin, which means the Moon must move away from Earth to conserve angular momentum. The problem here is that the age of the moon doesn’t fit today’s recessions rate and it has been suggested that the tides must have been much weaker for prolonged periods of Earth’s history. Numerical modelling efforts over the past decade have shown that the tides today are very large and a poor representation of past tides, and that for the past 1.5 Gyr, tidal dissipation rates have been around 45% of present-day values. Here, we present a new series of high-resolution simulations of Phanerozoic tides and discuss sensitivity to topography, forcing, and ocean stratification. The results confirm previous results about dissipation rates obtained at lower resolution. Furthermore, we apply proxies for tides collated from the geological literature for three selected periods (the Devonian, Jurassic, and Cretaceous) and show that our simulations mostly conform well with the proposed tidal characteristics from the proxies. The simulations also show that the most important controller of tides on long scales is tectonics: the locations of the continents set the size of ocean basins, and basins of the right size can host very large tides due to tidal resonance. Consequently, the supercontinent cycle generates a corresponding supertidal cycle with weak tides during supercontinent stages and a series of tidal maxima during the dispersion and assembly of the supercontinent.

How to cite: Green, M., Guo, B., Perez, I., Byrne, H., and Hadley-Pryce, D.: 1.5 Gyr of tides: how inaccurate are deep-time tidal model simulations?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4535, https://doi.org/10.5194/egusphere-egu23-4535, 2023.

Tide gauges remain the fundamental instrument for the determination of the absolute sea level and its variation over time. Following the establishment of the PYTHEAS national tide gauge network, which consists of five tide gauge stations located in strategic positions along the coastline of the government-controlled areas of the Republic of Cyprus, sea level observations were collected and analyzed. The main objective of this research is the determination, for the first time, of the most important tidal datums to support hydrographic surveying activities and promote critical environmental studies, such coastal erosion. Through the analysis of the data the following tidal datums were determined: Mean Sea Level (MSL), Mean Tide Level (MTL), Mean High Water (MHW), Mean Higher High Water (MHHW), Mean Low Water (MLW), Higher High Water (HHW) and Lower Low Water (LLW). These datums were estimated from sea level observations collected over the time span between January 2018 to April 2022. The dataset underwent through a complete quality control procedure, which was designed according to the latest international standards and included, among others, the influence of the tide gauge stability and the barometric pressure on the time series, and the detection and elimination of outliers. Furthermore, a thorough harmonic analysis was carried out, by means of the Harmonic Analysis Method of Least Squares (HAMELS), on the sea level observation dataset to highlight the effect periodic motions of the Earth, Sun and Moon have on local tide. In the context of this research, a total number of 68 tidal constituents were identified. Moreover, by using the Doodson X0 filter, the astronomical impact on the sea level was estimated by separating the astronomical influence component from the meteorological residuals. Data processing and analysis were carried out using custom in-house developed software. Finally, the estimated mathematical values of the tidal constituents, each of which describe a specific cosine curve, were utilized to calculate a tidal prediction up to December 2026.

How to cite: Nikolaidis, M. and Danezis, C.: Determination of Tidal Datums and Tide Characterization and Prediction in Cyprus via the PYTHEAS National Tide Gauge Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5480, https://doi.org/10.5194/egusphere-egu23-5480, 2023.

Sessile intertidal organisms are exposed to extreme variations in conditions during exposure (e.g., solar heating and desiccation) that can affect their health and development – and cause mass mortality events. Exposure is strongly dependent on the tides, which locally and regionally vary in magnitude, character, and phasing. Using the blue mussel Mytilus edulis as an example species, we hypothesise that organisms at locations that experience the lowest low tides during the middle of the day experience stronger heating than organisms at locations where the lowest tides occur during the early morning and early evening. In order to test this hypothesis, biomimetic loggers were calibrated to estimate mussel thermal characteristics and placed at two macro-tidal shores (North and South Wales, UK) dominated by semi-diurnal tides, which have a tidal phase difference of ~4 hours. At both locations, the highest temperatures were recorded when low tides occurred in the middle of the day; however, significantly higher temperatures were found for South Wales where spring low tides occur in the middle of the day and exposure durations are longer, whereas midday low tides in North Wales coincide with neap tides and shorter exposure durations. Our results suggest that heat stress for intertidal organisms may be more severe in intertidal areas where spring low tides occur in the middle of the day when solar radiation and air temperature are greatest. A global outlook will also be presented depicting potential high-risk zones for mussels and other sessile organisms. These results may be of importance for shoreline management and shellfish cultivation, especially with regards to future changing climate.

How to cite: Robins, P., Wilmes, S., Perks, E., Gimenez, L., and Malham, S.: The impact of tidal phasing on intertidal heat stresses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5875, https://doi.org/10.5194/egusphere-egu23-5875, 2023.

For a long time, characterization of aquifers has been mainly based on the monitoring of groundwater heads variations. This approach allowed to demonstrate that pressure changes induced by earth tides have a significant and measurable impact on groundwater heads monitored in confined aquifers. Nowadays efficient methods provide a direct estimation of groundwater fluxes. This is the case of the Finite Volume Point Dilution Method (FVPDM), a single-well tracer experiment that allows continuously monitoring and quantifying groundwater flux variations over time. Yet, the potential effect of earth tides on local groundwater flow has never been investigated. In this context, FVPDM tests have been performed in a confined aquifer in order to monitor groundwater fluxes over several tidal cycles. Results show significant groundwater flux variations over time (around 20% of the flux value), clearly correlated with pressure changes induced by earth tides. Subsurface heterogeneities could explain the fact that earth tides induce groundwater flow variations. Indeed, groundwater heads variations induced by earth tides depend on the local specific storage (in confined conditions) of aquifer. Any spatial variation of this parameter could induce variations of the hydraulic gradient and thus of groundwater fluxes. Therefore, these preliminary observations seem to open new perspectives for subsurface characterization by showing how groundwater flow variations measured in confined aquifer and induced by earth tides can be used as a marker of subsurface heterogeneities.

How to cite: Simon, N., Jamin, P., Dassargues, A., Nguyen, F., Caterina, D., and Brouyère, S.: Observations of the effect of earth tides on groundwater fluxes variations at the scale of a borehole, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6410, https://doi.org/10.5194/egusphere-egu23-6410, 2023.

    Thanks to its current accuracy and maturity, altimetry is considered as a fully operational observing system dedicated to various applications such as climate studies. Altimeter measurements are corrected from several geophysical parameters in order to isolate the oceanic variability and tide correction is one of the most critical. The accuracy of tidal models has been much improved for the last 25 years leading to centimetric accuracy in the open ocean. The last release of the global tidal model, referenced as FES2014b was distributed in mid-2016.

The underlying unstructured mesh resolution of FES2014b was increased in areas of interest like shallow waters and on the slope of the continental shelves, and the error of the pure hydrodynamic ocean solution has been divided by a factor of 2 compared to the previous version (FES2004). Still, some significant errors remain in some regions, due to the omission of compound tides and bathymetric errors (in shelf/coastal seas), seasonal sea ice effects, and lack of available data for assimilation (in the high latitudes).

To address the reduction of these errors and face the new challenges of the tide correction for HR altimetry, in particular, the forthcoming SWOT mission, a new global tide model FES2022 has been developed, focusing particularly on shallow waters and high latitudes.
This new tidal solution uses higher spatial resolution in coastal areas, extending systematically the model mesh to the narrowest coastal systems (fjords, estuaries, …), and the model bathymetry has been upgraded in many places thanks to an international collaboration effort. The hydrodynamic modeling benefits also from further improvements which allow producing very accurate hydrodynamic simulations. The use of the most recent altimeter standards and high inclination altimeters like Cryosat-2, Saral/AltiKa, and even Sentinel-3, also allowed retrieving some tide observations in the highest latitudes to help improving the polar tides modeling.

    Results show a great improvement in the FES2022 hydrodynamic solution compared to FES2014’s one. The assimilation procedure was conducted, and a specific loading tide solution was produced. The final FES2022 tidal solution was validated in comparison to the FES2014b, EOT20, GOT, and TPXO9v5 models, for the missions Jason 3, Sentinel-3A, and Cryosat-2.  Some validations of the new FES2022 tidal current are also presented here.

How to cite: Michel Lionel, T., Florent, L., Loren, C., Mathilde, C., Damien, A., Ergane, F., Mei-ling, D., Ramiro, F., Yannice, F., Gerald, D., and Nicolas, P.: The new FES2022 tidal atlas., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9008, https://doi.org/10.5194/egusphere-egu23-9008, 2023.

Simulations of the tides from the Last Glacial Maximum (26.5 – 19 kyr BP) to the present show large amplitude and dissipation changes, especially in the semi-diurnal band during the deglacial period. New reconstructions of global ice sheet history and sea levels covering the last glacial cycle allow us to extend the tidal simulations from the last interglacial (~125 kyr BP) to the present. Climate during this period was far from stable with periods of ice sheet advance and lower sea levels interspaced with ice sheet melting and sea level increases. Here, using the sea level and ice history from Gowan et al. (2021; 80 kyr BP to present) and sea level simulations based on the ICE6G_C ice history (Peltier et al., 2015; 122 kyr BP to present), we present simulations of tidal amplitudes and dissipation over the last glacial cycle using the tide model OTIS for the tidal constituents M₂, S₂, K₁ and O₁. Our results show large variations in amplitudes and dissipation over this period for the M₂ tidal constituent with several tidal maxima, whereas for the other constituents, changes are mainly regional. Due to the lower sea levels and altered bathymetry, open ocean dissipation was enhanced with respect to present day levels for most of the glacial cycle for all constituents. This result is important in the context of historical ocean mixing rates. We further highlight the impacts of the differences in bathymetry and ice sheet reconstructions on global tidal dissipation.

Gowan, E.J., Zhang, X., Khosravi, S., Rovere, A., Stocchi, P., Hughes, A.L., Gyllencreutz, R., Mangerud, J., Svendsen, J.I. and Lohmann, G., (2021), A new global ice sheet reconstruction for the past 80 000 years, Nature Communications, 12(1), 1-9.

Peltier, W. R., Argus, D. F., and Drummond, R. (2015), Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model, J. Geophys. Res. Solid Earth, 120, 450– 487, doi:10.1002/2014JB011176.

How to cite: Wilmes, S.-B., Pedersen, V. K., Schindelegger, M., and Green, M.: Evolution of tides and tidal dissipation over the last glacial cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9698, https://doi.org/10.5194/egusphere-egu23-9698, 2023.

Low-frequency non-astronomical changes of ocean tides of (1 cm) have been documented in water level measurements around the globe, but their causative mechanisms remain poorly understood in many cases. While anthropogenic developments (e.g., harbor dredging) are certainly a leading factor at individual sites, the spatially coherent tidal variability seen in areas with distributed tide gauge information is revealing of natural processes. Here we use a general circulation model, configured on a 1/12° horizontal grid, to spatially map the influence of ocean stratification changes on the global M₂ tide from 1993 to 2019. We partition the problem into separate yearly simulations of short duration (40 days) and relax each forward integration to the year’s “true” stratification, as provided by an eddying ocean reanalysis. The simulations reveal typical stratification-driven M₂ amplitude changes of 0.5 cm on interannual time scales, as calculated at positions of 40 coastal tide gauges in three particular regions (New Zealand & Australia, Florida & Gulf of Mexico, Northeast Pacific). Most of the identified fluctuations at the coast are present in the barotropic tidal component, suggesting an origin in changing tidal conversion at remote topography or turbulent energy dissipation in shallow water. In addition, we fit linear rates to the yearly M₂ solutions over the 1993–2019 time span and compare the resulting in-phase and quadrature trends to a novel (but still tentative) estimate of M₂ trends in the open ocean from TOPEX-Jason satellite altimetry. The two solutions bear gross resemblance to each other and indicate large spatial-scale trends of ~1 cm cy^-1 in the barotropic M₂ tide in the Indian Ocean, the western and northern Pacific (e.g., in the Gulf of Alaska), and Baffin Bay. Our results highlight that efforts seeking to explain interannual to secular changes of tides at the coast and in the open ocean must consider both sea level rise and contemporary changes in ocean stratification.

How to cite: Opel, L., Schindelegger, M., and Ray, R. D.: Impact of contemporary ocean stratification on the global tides: A preliminary modeling study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11720, https://doi.org/10.5194/egusphere-egu23-11720, 2023.

Internal tides, internal waves of tidal frequency, are generated by the flow of barotropic tidal currents over topography. Arabian Sea is a region of the northwestern Indian Ocean bounded to the east by the Indian peninsula. Though Arabian Sea and Bay of Bengal reside almost at the same latitudinal belt yet there is difference in the tide’s properties at the two basins. Internal tides in the Arabian Sea are complex and recent modeling studies have suggested that the semidiurnal internal tides show the largest seasonal variability among other regions in the world. However, the generation and propagation mechanism of internal tides, as well as their temporal variability, are unknown in this region. Therefore, we used in-situ observations collected at AD09 (8°N, 73°E) from November 2018 to December 2019 in this study. Salinity has a major role in governing the near-surface stratification, whereas temperature fluctuations govern the subsurface stratification at this location. The rectilinear zonal flow dominates the ellipticity of both semidiurnal and diurnal motions, indicating the generation of internal tides at the slopes. The maximum isopycnal displacement is observed during April at 100 m depth. Furthermore, the semidiurnal barotropic tides rotates in the clockwise direction, while the diurnal rotates in a counter-clockwise direction. Moreover, baroclinic semidiurnal tidal currents rotate anticlockwise at all depths, whereas diurnal tidal currents rotate both clockwise and anticlockwise at various depths. The strongest baroclinic currents, based on the magnitude of the semi-major axis for K₁ are found near 100 m, dominated by rectilinear flow, whereas for M₂, they are found at depths below 125 m. The maximum kinetic energy of the internal wave is observed at 90 m depth, and the analysis shows both diurnal and semidiurnal frequency dominates in the Arabian Sea, as the constituents M₂, S₂, K₁, and O₁ forms the most energetic part of the spectrum. In contrast, on the eastern part of the Indian peninsula in the Andaman Sea and Bay of Bengal, semidiurnal frequency dominates. Arabian Sea exhibits remarkable seasonal variability driven by the Indian monsoon system and seasonal variations in stratification influence the properties of internal tides in this basin. Hence, the study provides a major insight into the characteristics of internal tides over eastern Arabian Sea region.

How to cite: Makar, P., Rao, A. D., Badarvada, Y., and Pant, V.: Study of Internal Tides characteristics in the Eastern Arabian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13066, https://doi.org/10.5194/egusphere-egu23-13066, 2023.

Energetically consistent parameterizations of small-scale turbulent mixing rely on internal gravity wave energetics. A crucial ingredient is the generation of internal waves by the interaction of the barotropic tide with rough seafloor topography. Owing to the orientation of topographic obstacles and the directionality of barotropic tidal currents, this process is inherently anisotropic, but so far, this dependence on horizontal direction was not taken into account in global estimates of internal tide generation. We present the global application of a new method based on linear theory that resolves the horizontal direction of the internal tide generation, showing the substantial anisotropy of this process. How this in turn affects vertical mixing and the ocean state is evaluated with the aid of the internal gravity wave model IDEMIX, a backbone of energetically consistent parameterizations of wave-induced mixing.

How to cite: Pollmann, F., Nycander, J., Eden, C., and Olbers, D.: The anisotropy of internal tide generation: Global estimates for the M2 tide and implications for tidally driven mixing parameterizations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13302, https://doi.org/10.5194/egusphere-egu23-13302, 2023.

Ever since the Moon formed close to the Earth, it has been forced by tidal interactions to drift away through orbital angular momentum pumping. Available geological data provide snapshots of the lunar orbital history, the earliest registered to date at ~3.2 Ga. However, a complete theoretical reconstruction of the lunar orbit, which traces its evolution from the present state to a post-impact nosy neighbor at ~4.5 Ga was missing. Namely, previous tidal models attempting this reconstruction are either empirical, or numerically costly, and are always incompatible with the well-constrained lunar age. We undertake a systematic exploration of the time-varying tidal dissipation in the Earth’s oceans and solid interior to provide, for the first time, a history of the lunar orbit that fits the present measurement of its recession and the estimated lunar age. Our work extends a lineage of earlier works on the semi-analytical treatment of fluid tides on varying bounded surfaces, allowing us to mimic the time-varying effect of continentality on Earth. We further couple the oceanic response with solid bodily tidal deformations using an Andrade rheology. The modeled oceanic tidal response is effectively barotropic and is parametrized by only two parameters describing the oceanic thickness and the timescale of dissipation. Our resulting tidal response reconstructs a history of the lunar orbit that is predominantly shepherded by robust resonant excitations in the Earth’s paleo-oceans. This lunar orbital reconstruction is in good agreement with the available geological proxies, which predicates the dominance of long-wavelength flows in controlling the tidal history, instead of the continentality-driven basin modes. The generated tidal resonances caused significant and, relatively, rapid variations in the lunar semi-major axis, the Earth’s length of the day, and the Earth’s obliquity. Consequently, these astronomical features should have driven significant paleo-climatic variations through tidal heating and the changing insolation.

How to cite: Farhat, M., Auclair-Desrotour, P., Boué, G., and Laskar, J.: The resonant tidal evolution of the Earth-Moon distance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14664, https://doi.org/10.5194/egusphere-egu23-14664, 2023.

The lunar semidiurnal (M₂) tide of the Gulf of Maine and Bay of Fundy is remarkable not only for its large amplitude but also for its spatially coherent temporal changes of ∼1–3 cm on secular to seasonal time scales. Previous work suggests a role for ocean stratification in causing the tide's seasonal modulation, while the forcing factors for lower-frequency M₂ variability are yet unknown. Here I show, using a regional baroclinic modeling framework, that changes in ocean stratification also matter on interannual time scales and account for ∼40% of the observed M₂ changes at tide gauges from 1994 to 2019. Masking experiments and energy diagnoses reveal that the modeled variability is primarily driven by fluctuations in barotropic-to-baroclinic energy conversion on the continental slope south of the gulf's mouth, with a ∼7% (0.30 GW) drop in the area-integrated conversion rate inducing a 1-cm amplitude increase along the Massachusetts coast. Evidence is given for the same process to have caused the near-monotonic M₂ amplitude decrease throughout the 1980s, as slope waters warmed due to a northerly shift of the Gulf Stream. I present results from model-based M₂ projections for the end of the 21^st century and highlight possibly competing roles of stratification changes and sea level rise in driving the tide's response to future climate change.

How to cite: Schindelegger, M.: On seasonal to secular M2 variability in the Gulf of Maine, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17440, https://doi.org/10.5194/egusphere-egu23-17440, 2023.

Natural processes and anthropogenic activities often generate changes in the stress state of the crust, and, consequently, measurable surface deformation. Volcanic activity produces surface displacements as a result of phenomena including magma recharge/deployment and migration, and fluid flow. The accurate measurement of surface deformation is one of the most relevant parameters to measure tectonic stress accumulation and for studying the seismic cycle. Improved monitoring capabilities also capture surface deformations related to coastal erosion and its connection to climate change, landslides and deep seated gravitational slopes, and other hydrogeological hazards. In addition, anthropogenic activity such as mining and water pumping cause measurable soil displacement.

Ground deformations are measured by space and terrestrial techniques, reaching sub-millimetric accuracy. Synthetic Aperture Radar (SAR) satellites have been quickly developing in the last decades. GNSS data allows to map nearly 3D deformation patterns, but often the network consists of few benchmarks. The joint use of SAR and GNSS data compensate the intrinsic limitations of each technique. Levelling measures the geodetic height of a benchmark. Borehole dilatometers and clinometers provide derivative measurements of the surface displacements.

Theoretical models of deformation sources are commonly employed to investigate the surface displacements observed, for example, in volcanic areas or related to a seismic event. A volcanic source can be represented by a confined part of crust with a certain shape inflating/deflating because of a change in the internal magma/gas pressure. The static seismic source is ideally represented by a tabular discontinuity in the crust undergoing relative movement of both sides. Furthermore, gas reservoir exploitation, water pumping and soil consolidation, can be represented using the same models.

Volcanic and Seismic source Modelling (VSM) is an open-source Python tool to model ground deformation detected by satellite and terrestrial geodetic techniques. It allows the user to choose one or more geometrical sources as forward model among sphere, spheroid, ellipsoid, fault, and sill. It supports geodetic from several techniques: interferometric SAR, GNSS, levelling, Electro-optical Distance Measuring, tiltmeters and strainmeters. Two sampling algorithms are available, one is a global optimization algorithm based on the Voronoi cells and the second follows a probabilistic approach to parameters estimation based on the Bayes theorem. VSM can be executed as Python script, in Jupyter Notebook environments or by its Graphical User Interface. Its broad applications range from high level research to teaching, from single studies to near real-time hazard estimates. Potential users range from early career scientists to experts. It is freely available on GitHub (https://github.com/EliTras/VSM). In this contribution I show the functionalities of VSM and test cases.

How to cite: Trasatti, E.: Volcanic and Seismic source Modelling (VSM) - An open tool for geodetic data modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2589, https://doi.org/10.5194/egusphere-egu23-2589, 2023.

Volcanic eruptions are often preceded by episodes of inflation and emplacement of magma along tensile fractures. Here we study the 2021 Cumbre Vieja eruption on La Palma, Canary Islands, and present evidence for tensile fractures dissecting the new cone during the terminal stage of the eruption. We use synthetic aperture radar (SAR) observations, together with drone images and time-lapse camera data, to determine the timing, scale and complexities associated with the fracturing event, which is diverging at a topographic ridge. By comparing the field dataset with analogue models, we further explore the details of lens-shaped fractures that are characteristic for faults diverging at topographic highs and converging at topographic lows. The observations made at Cumbre Vieja and in our models are transferrable to other volcanoes and add further evidence that topography is substantially affecting the geometry and complexity of fractures and magma pathways, and the locations of eruptions.

How to cite: Walter, T. R., Zorn, E., Gonzalez, P., Sansosti, E., Munoz, V., Shevchenko, A., Plank, S., Reale, D., and Richter, N.: Late complex tensile fracturing interacts with topography at Cumbre Vieja, La Palma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3344, https://doi.org/10.5194/egusphere-egu23-3344, 2023.

Geophysical and geological data acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago in the North Mozambique Channel. More than 2200 submarine volcanic edifices, comparable to the Fani Maoré volcano, have been identified. Most of them are distributed according to two large submarine tectonic-volcanic fields: the N’Drounde province oriented N160°E north of Grande-Comore Island, and the Mwezi province oriented N130°E north of Anjouan and Mayotte Islands. The presence of popping basaltic rocks sampled in the Mwezi suggests post-Pleistocene volcanic activity. The geometry and distribution of recent structures observed on the seafloor are consistent with a current regional dextral transtensional context. Their orientations change progressively from west to east (∼N160°E, ∼N130°E, ∼EW). In the western part, the volcanism could be influenced by the pre-existing structural fabric of the Mesozoic crust. The wide tectono-volcanic corridor underlines the incipient Somalia–Lwandle dextral lithospheric plate boundary between the East-African Rift System and Madagascar. For details see Thinon et al. (2022;  doi 10.5802/crgeos.159).

How to cite: Thinon, I., Lemoine, A., Leroy, S., Paquet, F., Berthod, C., Zaragosi, S., Famin, V., Feuillet, N., Boymond, P., Masquelet, C., Rusquet, A., and Mercury, N. and the SISMAORE and COYOTES teams: Volcanism and tectonics unveiled in the Comoros Archipelago between Africa and Madagascar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5046, https://doi.org/10.5194/egusphere-egu23-5046, 2023.

The Krafla Volcanic System (KVS) in the Northern Volcanic Zone (NVZ) in Iceland last erupted between 1975 and 1984, during an eruptive period called “the Krafla Fires”. The KVS is composed of a restless caldera, an array of scoria cones along a fissure swarm and is among the best-studied volcanic systems due to the exploitation of its geothermal potential. In 2009, the Icelandic Deep Drilling Project (IDDP) encountered a shallow rhyolitic magma body at 2.1 km depth beneath the caldera. To date, no geophysical method has been able to image this magma body at Krafla within the top 4 km of the crust.

  Here we present new micro-gravity data collected in June and July 2022 across a 14-station network of benchmarks in the KVS. Micro-gravimetry is a relative method that records changes in gravity between a reference and a series of benchmarks over both space and time to investigate subsurface mass or density changes via time-series analysis and modelling.

  Our 2022 survey highlights negative gravity differences of benchmarks located in the centre of the caldera with respect to a reference located to the south and outside the caldera. The most negative values are found in its eastern part. Positive gravity differences can be found south of the southern caldera wall along a set of past eruptive fissures.

  The next steps in data processing include data reduction for deformation effects to link the new data to previous joint deformation and micro-gravity surveys conducted at the KVS since 1965. This should enable us to quantify the long-term evolution of the KVS over more than 50 years providing unprecedented insights into its inner workings.

How to cite: Martinez Garcia, A., Gottsmann, J., and Rust, A.: The long-term evolution at Krafla Volcanic System, Iceland, by time-lapse microgravity., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5163, https://doi.org/10.5194/egusphere-egu23-5163, 2023.

Forecasting eruption is the ultimate challenge for volcanology. While there has been some success in forecasting eruptions hours to days beforehand¹, reliable forecasting on a longer timescale remains elusive. Here we show that magma inflow rate, derived from surface deformation, is an indicator of the probability of magma transfer towards the surface, and thus eruption, for basaltic calderas. Inflow rates ≥0.1 km³/year promote magma propagation and eruption within 1 year in all assessed case studies, whereas rates less than 0.01 km³/year do not lead to magma propagation in 89% of cases. We explain these behaviours with a viscoelastic model where the relaxation timescale controls whether the critical overpressure for dike propagation is reached or not. Therefore, while surface deformation alone is a weak precursor of eruption, estimating magma inflow rates at basaltic calderas provides improved forecasting, substantially enhancing our capacity of forecasting weeks to months ahead of a possible eruption.

How to cite: Acocella, V., Galetto, F., Hooper, A., and Bagnardi, M.: Forecasting the fate of unrest at basaltic calderas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5317, https://doi.org/10.5194/egusphere-egu23-5317, 2023.

Countries with low to lower-middle income have limited resources to deploy and maintain ground monitoring networks. In this context, satellite-based techniques such as Radar interferometry (InSAR) is a great solution for detecting volcanic ground deformation at regional-scale. With the launch in 2014 of Sentinel-1 mission, regional monitoring of volcanic unrest becomes easier as SAR data are freely available with a revisit time of 6-12 days. Here, we develop a tuned processing workflow to produce Sentinel-1 InSAR time series and to automatically detect volcanic unrest over 80 volcanic systems located along the East African Rift System (EARS). First, we show that the correction of atmospheric signals for the arid and low-elevation EARS volcanoes is less important than for other volcanic environments. For a 5-year times series (between Jan. 2015 and Dec. 2019), we show that statistically uncertainties in InSAR velocities are around 0.1 cm/yr, whereas uncertainties associated with the choice of reference pixel are typically 0.3–0.6 cm/yr. For the automatic detection, we found that volcanic unrest can be detected with high confidence in the case the cumulative displacements exceed three times the temporal noise (threshold of 3σ). Based on this criterion, our survey reveals ground unrest at 16 volcanic centres among the 38 volcanic centres showing historical evidence of eruptive or unrest activity. A large variety of processes causing deformation occurs in the EARS: (1) subsidence due to contraction of magma bodies at Alu-Dalafilla, Dallol, Paka and Silali; (2) subsidence due to lava flows compaction at Kone and Nabro; (3) subsidence due to fluid migration at Olkaria and Aluto or fault-fluids interactions at Haludebi and Gada Ale; (4) rapid inflation due to magma intrusions at Erta Ale and Fentale; (5) short-lived inflation of shallow reservoirs at Nabro and Suswa; (6) long-lived inflation of large magmatic systems at Corbetti, Tullu Moje and Dabbahu. Except Olkaria and Kone, all these volcanoes were identified as deforming by previous satellites missions (between late 90’s and early 2000), which is an indication of the persistence of activity over long-time scales (>10 years).  Finally, we fit the time series using simple functional forms and classify seven of the volcano time series as linear, six as sigmoidal and three as hybrid, enabling us to discriminate between steady deformation and short-term pulses of deformation. We found that the characteristics of the unrest signals are independent of the expected processes, which means that additional information (structural geology, seismicity, eruptive history and source modelling) will be necessary to characterize the processes causing the unrest. Our final objective will be to improve the transfer of this information to local scientists in Africa, which can be achieved by integrating our tools to an existing monitoring system and by developing web-platform where the InSAR products can be freely available.

How to cite: Albino, F., Biggs, J., Lazecký, M., Maghsoudi, Y., and McGowan, S.: Regional-scale ground monitoring of 80 East African Rift volcanoes using Sentinel-1 SAR interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5609, https://doi.org/10.5194/egusphere-egu23-5609, 2023.

Investigation of the dynamic magma movement beneath the volcanos could provide critical information about the mechanism of volcanic eruption and therefore enhance the accuracy of eruption forecast.  Axial Seamount is an active submarine volcano located at the intersection of the Juan de Fuca Ridge and the Cobb hotspot.  Through its submarine surveillance network of Ocean Observatories Initiative (OOI), we observed magmatic activities that occurred before and during its latest eruption on April 24, 2015, as well as the following unrest events from the temporal variations of shear-wave velocity beneath Axial Seamount.

In this study, we applied the Rayleigh-wave admittance method, which uses the frequency-domain transfer function between seismic displacement and water pressure, to invert for shear-wave velocity changes beneath the submarine seismic stations.  The results illustrated that a large magma upwelling event happened beneath the AXEC2 (southeastern caldera of Axial Seamount) several weeks prior to its 2015 eruption, implying the magma movement through a pathway near the southeastern caldera and possibly triggered the subsequent eruption.  However, another magma upwelling event beneath the AXID1 station (southern caldera) between December 2016 and June 2017 occurred without triggering any noticeable eruption event. These magmatic activities demonstrate that the eruption of Axial Seamount is controlled by a complicated magma plumbing system.  The eruption probably depends on not only the magma influx but also the status of the plumbing system and the overlying crustal layer.  With the Rayleigh-wave admittance method and the real-time data from the OOI network, we can continuously monitor the status of Axial Seamount and provide more information for the next eruption.

How to cite: Wang, L. and Ruan, Y.: Dynamic magma movements beneath the Axial Seamount revealed by Rayleigh-wave Admittance Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5843, https://doi.org/10.5194/egusphere-egu23-5843, 2023.

One of the best-known examples worldwide of monogenetic volcanism is the Parícutin volcano. The eruption began its formation in the middle of a cornfield in February 1943 and lasted until March 1952. Parícutin is the youngest edifice of the Michoacán-Guanajuato Volcanic Field, which was witness initially by local inhabitants, and later by scientists and other observers. Observations of the eruption documented the remobilization of primary ashfall by rainfall and wind. Despite these observations, the resulting reworked deposits have not yet been described in the stratigraphic sequence. The distinction between primary pyroclastic and reworked deposits is critical for the geological understanding of eruptive processes and related hazards because of their different origins, frequencies, and environmental impacts. This categorization is not always obvious and needs a detailed study to characterize the complex interbedding of both types of deposits that coexist in the volcanic sequence. Referenced to these, we conducted new field reconnaissance, coupled with laboratory analyses of the ejecta ash fraction. The detailed composite stratigraphy obtained consists of six widely dispersed fallout deposits interbedded with seven reworked units. These reworked deposits display sedimentary structures produced by tephra remobilization due to lahars and stream flows. In addition, some layers show dunes and ripples generated by duststorms. By using GIS tools, we integrated the existing data with our new composite stratigraphic column and the distribution map of the syn-eruptive reworked deposits. This analysis reveals that more than 70% of the total thicknesses correspond to syn-eruptive reworked deposits. Therefore, previous studies had overestimated the distribution of primary tephra from the Parícutin explosive phases. The lowest and flattest areas with wide rill networks, which are located 4 to 6 km north of the volcano, are composed of up to 90% reworked deposits. In contrast, proximal locations with gentler slopes located at medium altitudes better preserve pyroclastic deposits. To that end, we constructed a new isopach map of the pyroclastic deposits based on the distribution of the reworked deposits. This study brings new light to understanding the sedimentary processes that occur during volcanic eruptions and highlights the importance of recognizing pyroclastic and reworked deposits during monogenetic eruptions.

How to cite: Bolós, X., Macias, J. L., Ocampo-Díaz, Y. Z., and Tinoco, C.: Reworking processes during monogenetic eruptions. The case of the Parícutin volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5994, https://doi.org/10.5194/egusphere-egu23-5994, 2023.

The Hawaii-Emperor seamount chain stretches westward from the “Big Island” of Hawaii for over 6000 km until the oldest part of the Emperor chain is subducted at the Kuril and Aleutian trenches. Still regarded as the iconic hotspot-generated seamount chain it has been sampled, mapped, and studied to give insights into numerous oceanic phenomena, such as seamount and volcano formation and associated intraplate magma budgets, the past absolute motions of the Pacific plate and the drift of the Hawaiian plume, and the thermal and mechanical properties of oceanic lithosphere. Much early work on determining the flexural rigidity and equivalent elastic plate thickness that supports the large volcano loads that comprise the chain was focussed on the Hawaiian Ridge, with a major multichannel seismic expedition to the Hawaiian Islands in 1982 providing clear and direct evidence of plate flexure, as well as the indirect effect this deformation has on Earth’s gravity field. Numerous studies have since followed. However, the older part of the chain, beyond the ~50 Ma “bend”, has been much less well studied due to its remoteness, but recent expeditions have provided new marine seismic data to allow an estimation of elastic thickness along the Emperor chain and how they compare to the information we have along the Hawaiian Ridge. Here, we present preliminary work on determining the elastic thickness beneath the Emperor Seamounts. Unlike the Hawaiian Ridge, where the age of the lithosphere at the time of loading (i.e., the difference in age between the underlying seafloor and the formation age of a seamount or oceanic island) is remarkably constant, along the Emperor chain there are major variations in the age of loading, compounded by higher uncertainty due to limited seamount age sampling and the chain’s location within the Cretaceous Quiet Zone. Thus, models with variable elastic thickness as a function of location along the Emperor chain are required. In this presentation, we discuss several models that seek to account for the new seismic imaging of the top and base of flexed oceanic crust (i.e. Moho) at Jimmu guyot while at the same time honouring the characteristic gravimetric signature of the Emperor seamount edifices and their flanking moats. The Optimal Regional Separation (ORS) method is used to isolate the flexural loads, while seismic tomography and different velocity/density relations are explored for assigning suitable load and infill densities that vary spatially, and we search for optimal density and elastic parameters which minimize the misfit to both the residual gravity as well as the seismically observed flexure in the vicinity of Jimmu guyot. The first-order result is a clear thinning of the elastic thickness as we move from south to north: the implications of which we examine here for the tectonic evolution of the northwest Pacific Ocean and the long-term (>10⁶ a) mechanical properties of oceanic lithosphere.

How to cite: Wessel, P., Watts, T., Xu, C., Boston, B., Cilli, P., Dunn, R., and Shilington, D.: Variation in Elastic Thickness along the Emperor Seamount Chain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6118, https://doi.org/10.5194/egusphere-egu23-6118, 2023.

Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.

Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (P_o = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).

Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (P_o  ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.

How to cite: Drymoni, K., Tibaldi, A., Pasquaré Mariotto, F., and Bonali, F. L.: Dyke-sill propagation in glacial-volcanotectonic regimes: The case study of Stardalur laccolith, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6230, https://doi.org/10.5194/egusphere-egu23-6230, 2023.

Assessing the history, dynamics and magnitude of pre-historic explosive volcanic eruptions relies heavily on the completeness of the stratigraphic records, the spatial distribution, and the sedimentological features of the pyroclastic deposits. Near-vent volcanic successions provide fundamental but often patchy information, both in terms of record completeness (e.g., scarce accessibility to the older deposits) and of the spatial variability of the sedimentological features. Hence, medial to distal sections increasingly represent essential integrative records.

Campi Flegrei (CF) is among the most productive volcanoes of the Mediterranean area, with a volcanic history comprised of well-known caldera-forming eruptions (e.g., Campanian Ignimbrite, CI, ~40 ka; Neapolitan Yellow Tuff, NYT, ~14 ka). Furthermore, recent studies correlated a well-known widespread distal ash layer, the so-called Y-3, with a poorly exposed proximal CF pyroclastic unit (Masseria del Monte Tuff, 29ka), allowing a re-assessment of the magnitude of this eruption, now recognized as a third large-magnitude (VEI 6) eruption at CF. The discovery of this large eruption reduces drastically the recurrence intervals of large-magnitude events at CF and has major implications for volcanic hazard assessment.

While the most powerful Late Pleistocene (e.g., post-NYT and partially post-CI) eruptions at CF have been the subject of extensive investigations, less is known about its earliest activity. Motivated by this knowledge gap, we have reviewed the research on Middle-Late Pleistocene eruptions from the CF (~160-90 ka) in light of new compositional (EMPA + LA-ICP-MS), grain-size distribution (dry/wet sieving and laser) and morphoscopy (SEM) data of tephra layers from proximal and distal settings, including inland and offshore records. Our study provides a long-term overview and cornerstone that will help provide future eruptive scenarios, essential for the quantification of recurrence times of explosive activity and in volcanic hazard assessment in the Neapolitan area. This overview sets the basis for modelling dispersion as well as eruptive dynamics parameters of pre-CI large-magnitude eruptions, needed to better understand the behavior of the CF caldera with a long-term perspective.

How to cite: Fernandez, G., Giaccio, B., Costa, A., Monaco, L., Albert, P., Nomade, S., Pereira, A., Leicher, N., Lucchi, F., Petrosino, P., Milia, A., Insinga, D., Wulf, S., Kearney, R., Veres, D., Jordanova, D., and Sottili, G.: New constraints on Middle-Late Pleistocene large-magnitude eruptions from Campi Flegrei, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6552, https://doi.org/10.5194/egusphere-egu23-6552, 2023.

In this research, the Interferometric Synthetic Aperture Radar (InSAR) method is used to evaluate the connection between earthquakes and volcano dynamics in Azerbaijan. InSAR provides a robust technique for defining the complexity of earthquakes in spatial dimensions and provides more precise information about the effects of earthquakes than traditional methods. We assessed pre-, co-, and post-seismic scenarios to find the possible triggering relationships between moderate earthquakes and the Ayazakhtarma mud volcano. The Ayazakhtarma volcano is located 46 km from the 2021 Shamakhi and 67 km from the 2019 Basqal earthquakes, respectively. In this study, comprehensive deformation time series and velocities for the volcano using Sentinel 1A/B data between 2014 and 2022 were produced from LiCSAR products using LiCSBAS. At the same time, a radar line-of-sight (LOS) displacement map was generated based on results from the GMT5SAR for pre-, co-, and post-seismic deformation of earthquakes. Based on our observations of the following earthquakes, our results show that moderate earthquakes (Mw≤5) cannot trigger large mud volcano eruptions. In particular, the study of the Ayazakhtarma mud volcano revealed significant LOS changes that were positive and negative in the western half and eastern half of the site, respectively. Our research helps us comprehend how earthquakes impact eruptive processes. In two different situations, the interferograms enable the detection of ground displacement associated with mud volcano activity. At the Ayazakhtarma, faults also play a fairly important role in the deformation pattern. Interestingly, the observed fault system primarily exists in the region that divides sectors with various rates of subsidence. The interferometric data have been studied, providing new information on the deformation patterns of the Ayazakhtarma mud volcano.

How to cite: Gadirov (Kadirov), F. and Ahadov, B.: The Relationship Between Moderate Earthquakes and Ayazakhtarma Mud Volcano Using the InSAR Technique in Azerbaijan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6906, https://doi.org/10.5194/egusphere-egu23-6906, 2023.