The validation of compatibility and long-term stability of absolute gravimeters is a key component for the realization of the International Terrestrial Gravity Reference Frame (ITGRF) of IAG and is relevant for metrology, in particular for the realization of the kilogram. Because a natural reference for the absolute value of gravity acceleration is not accessible, international comparisons of absolute gravimeters are well established. The gravity reference is realized based on a set of accurate absolute measurements and the functional model for their processing. 
After the CCM.G-K2.2023 key comparison supplemented by additional comparison ICAG-2023 held in September 2023 at Table Mountain Geophysical Observatory (TMGO) Boulder, Colorado, USA, there was a need to distribute the gravity reference further to institutions in Europe. Therefore, the EURAMET key comparison of absolute gravimeters EURAMET.M.G-K2.2023 and additional comparison WETCAG-2024 was organized at the Geodetic Observatory Wettzell, Germany, in May and June 2024, where 15 institutions participated with 17 absolute gravimeters. The link to CCM.G-K2.2023 is provided by three gravimeters that took part in both comparisons. Additionally, deviations from the verticality and Eötvös/Coriolis accelerations during the free fall were determined for most of the gravimeters. 
We present first results for the equivalence of the participating gravimeters as well as for the verticality and Eötvös effects. Further, we evaluate and discuss the stability of the reference values over decades, based on a reference function deduced from the registration of the superconducting gravimeter GWR SG030, repeated absolute gravity observations since 2010 and several regional comparisons performed at this station, in particular with the comparison EURAMET.M.G-K3 held at Wettzell in 2018. 
Quantum gravimeters are represented in WETCAG-2024 with two instruments. This allows to compare the new technology with the reference established at the Wettzell station over 15 years, specifically in the context of stability of gravimeters and the upcoming realization of the ITGRF.  

How to cite: Wziontek, H., Pálinkáš, V., Antokoletz, E. D., Baumann, H., Bernard, J.-D., Bilker-Koivula, M., Brachmann, E., Ciesielski, A., Contrafatto, D., Dykowski, P., Engfeldt, A., Facello, A., Gebauer, A., Greco, F., Iacovone, D., Janák, J., Konrad, J., Kostelecký, J., Lothhammer, A., Merlet, S., Messina, A., Näränen, J., Papčo, J., Prato, A., Reich, M., Reudink, R., and Rothleitner, C.: First results from the comparison of absolute gravimeters WETCAG-2024 at the Geodetic Observatory Wettzell, Germany, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4113, https://doi.org/10.5194/egusphere-egu25-4113, 2025.

Ocean tide variability can be decomposed into a vast spectrum of individual partial tides with distinct tidal periodicities. Besides the ~10 dominant frequencies well constrained by satellite altimetry, there is a wide range of smaller oscillations that are much less well determined by observations. Besides other tidal subgroups (e.g., radiational tides and degree-3 ocean tides) these comprise hydrodynamically nonlinear ocean tides, which are generated due to the interactions of major tides. The frequencies of these tides are the sums and differences of the generating major tides and do not necessarily have a counterpart in the tide-generating potential. Nonlinear ocean tides possess significantly large amplitudes, especially in shallow waters as they can be found along the coast of the North Sea in Northern Germany.
We present in this contribution new hydrodynamical simulations of the global dynamics of non-linear ocean tides with the numerical shallow-water model TiME (Tidal Model forced by Ephemerides; Sulzbach et. al, 2021). The simulations benefit from an online implementation of self-attraction and loading, which can simultaneously represent this effect for ocean tides from long to sub-semidiurnal periods. Additionally, the model employs an updated implementation of bottom friction, which considers the shear within the vertical flow direction of the tidal transport. The model results are validated with a network of terrestrial superconducting gravimeters, which are sensitive to both local and global mass anomalies induced by ocean tides. Therefore, gravimeters are not only sensitive to the local sea surface anomaly but integrate this information over a larger area. As they additionally possess a very low noise level and their respective time series have considerable length, gravimeters are well suited to detect these spatially extended mass anomalies of low amplitude. Periods considered in this work range from 1 month down to 4 hours. Depending on the generation type of the different nonlinear tides it can be shown that the observed tidal variability can be well reduced by employing TiME predictions for selected frequencies.

How to cite: Dobslaw, H., Sulzbach, R., Voigt, C., and Wziontek, H.: Modeling a broad spectrum of hydrodynamically nonlinear ocean tides and their observation by continuously recording terrestrial gravimeters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20592, https://doi.org/10.5194/egusphere-egu25-20592, 2025.

Repeated and continuous gravity measurements have long been performed to monitor active volcanoes and study the processes that may lead to unrest and eruptions. Possible instrumental effects must be accurately accounted for, since they can be behind apparent gravity changes even stronger than the real (i.e., volcano-related) ones.

At tall volcanoes, where, due to the rough topography, the difference between the gravity field values at external and summit stations can be hundreds of mGal, strong time changes in gravity may arise from changes in the calibration factor of the device used to perform campaign measurements. For example, a difference in the value of the gravity field between reference station and summit active area of 300 mGal implies an apparent time change of 60 µGal, if a shift of 100 ppm occurs in the calibration factor of the gravimeter. To avoid this, the calibration factor of the instrument used to perform campaign measurements should be regularly checked.

The instrumental drift of relative gravimeters can make it difficult to detect long-term (months to years) gravity changes through continuous measurements. This shortcoming may also affect data from superconducting gravimeters (much more stable than spring gravimeters), especially if relatively small gravity changes are to be detected over time scales of several months, or longer. To address this issue, absolute gravity measurements must be performed at the same site where the continuously recording gravimeter is installed. Here we present some examples from Mt. Etna volcano, where instrumental effects, potentially leading to apparent time changes of some tens of µGal, were detected through suitable measurement strategies.

How to cite: Greco, F., Carbone, D., Contrafatto, D., Messina, A. A., and Mirabella, L. T.: On the importance of accounting for instrumental effects when applying gravimetry to volcano monitoring, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10971, https://doi.org/10.5194/egusphere-egu25-10971, 2025.

We present a project from the research unit (RU) "TIME" (Clock Metrology: A Novel Approach to TIME in Geodesy), which seeks to determine gravity potential or height differences between distant locations by comparing optical clocks. A strontium optical lattice clock at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig will be connected to the German Research Centre for Geosciences (GFZ) in Potsdam via a delay-compensated optical fiber link. Optical time transfer will then be applied between the geodetic observatories in Potsdam and Wettzell (hosting a second optical clock) through the Atomic Clock Ensemble in Space (ACES) using Satellite Laser Ranging (SLR) telescopes.

Additionally, a third optical clock located in Grasse, France, will be included for comparison. This clock, assumed to have similar characteristics to the one in Braunschweig, will connect to PTB via microwave terminals and to Wettzell using both laser and microwave links, forming a triangular measurement configuration.

The innovative aspect of this approach lies in utilizing time transfer, rather than frequency transfer, and employing free-space links over an extended period to measure physical height differences. Key challenges include managing clock and link variations, atmospheric disturbances, visibility limitations, and data gaps. The clock and link errors are modeled specifically for this constellation, involving the ACES system.

This approach demonstrates the accurate determination of physical height differences via time transfer, particularly for Global Geodetic Observing System (GGOS) core stations such as the Geodetic Observatory Wettzell (GOW).

We discuss the underlying principles, unique properties, and specific challenges of this measurement scenario. Additionally, we provide preliminary estimates of the expected accuracies for the various components and the resulting height differences, based on simulations with varying error budgets for comparison.

We acknowledge the support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 490990195 – FOR 5456.

How to cite: Lachmann, K. E., Müller, J., Schlicht, A., and Vollmair, P.: Determination of physical heights via time transfer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15763, https://doi.org/10.5194/egusphere-egu25-15763, 2025.

Absolute gravity measurements at the level of 1 µGal using cold atom quantum technology have been demonstrated in the laboratory in 1992 and have ever since received an increasing interest from the geophysics community [1]. In 2015, Exail launched on the marketplace the Absolute Quantum Gravimeter (AQG) [2]. Cutting-edge technology developments brought the necessary easy-of-use, autonomy, and robustness for field deployment.

In 10 years of production, more than 20 units have since been produced for various geophysical applications, including hydrology and volcanology. We present here an overview on the results obtained over this large panel of instruments. Comparison of the sensitivity of the instruments at our premises prior to shipping, shows reproducible performance in the range of 600-800 nm/s²/sqrt(Tau), reaching a stability better than 10 nm/s² after approximately one hour of integration.

Ongoing work focuses on two main axes: the completion and improvement of a budget of systematic effects, that is necessary to evaluate the trueness of the instruments, several instruments already delivered with such a budget; and the improvement of remote operability with the development of a self-leveling tripod.

[1] M. Kasevich, S. Chu. Measurement of the gravitational acceleration of an atom with a light-pulse atom interferometer. Applied Physics B, 1992, vol. 54, p. 321-332.
[2] V. Ménoret et al, Gravity measurements below 10-9 g with a transportable absolute quantum gravimeter. Scientific Reports, 2018, 8, pp.12300.

How to cite: Richard, J., Antoni-Micollier, L., Gautier, R., Bertier, P., Vermeulen, P., Janvier, C., Majek, C., Desruelle, B., and Menoret, V.: Absolute Quantum Gravimeter for Field Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11309, https://doi.org/10.5194/egusphere-egu25-11309, 2025.

Quantum gravimeters have been in use as laboratory instruments by various research groups for some time and have been available as user-friendly commercial devices since 2014. In contrast to traditional absolute gravimeters such as the FG5, which employ corner cubes as a falling test mass, these devices utilise laser-cooled cold-atom clouds. The Absolute Quantum Gravimeter (AQG) produced by the French company Exail is available in two model series: indoor observatory devices (A-series) and outdoor capable devices (B-series).

In this contribution, we present the results of the world's first AQG comparison, conducted in January 2024 at Leibniz University Hanover (Germany) in the gravimetric laboratory of the HiTec building.

Five AQG units (B-series) participated in the comparison, operated by teams from France, Poland and Germany. The measurement activities were conducted over a five-day period, comprising 12-hour tracking series conducted both during the day and night. In contrast with traditional gravity comparisons, the primary objective of these joint measurements was to enhance the understanding of the operational principles of AQGs. In addition to the long measurements each device carried out on 3 out of 5 available pillars, dedicated tests were conducted jointly on all instruments, including tiltmeter calibrations and accelerometer response. The data processing and evaluation focused on device characteristics, stability over time, individual noise levels, and statistical uncertainties of individual measurements.

The joint AQG measurements were independently supported by classical relative and absolute gravity measurements with CG6 and FG5 gravimeters.

How to cite: Merlet, S., Reich, M., Dykowski, P., Vermeulen, P., Arnal, M., Gebauer, A., Sobh, M., Addi, N., Le Moigne, N., Thoss, H., Sekowski, M., Bergmann, J., and Timmen, L.: Results and Findings from the Worldwide First Joint Measurements with 5 Absolute Quantum Gravimeters, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16499, https://doi.org/10.5194/egusphere-egu25-16499, 2025.

The Horizon Europe project “Qu-Test” [1] aims to establish a European infrastructure open to industry for the characterization and testing of components, subsystems, and instruments developed from quantum technologies. As part of this project, led by a consortium of Research Technology Institutes and National Metrology Institutes within the European Union, we are developing a platform for the functional and metrological characterization of quantum gravimeters.

In my poster, I will present our reference site, which comprises our laboratory, characterized instruments, and models derived from 20 years of measurements.

Our laboratory, located in the Paris region, features a 6 m × 5.5 m × 2 m concrete platform supported by 12 m long legs that reach the Fontainebleau sands layer. Initially constructed for the LNE Watt Balance [2], our activities have since expanded to include the use, study, characterization, and calibration of various types of instruments. Relative spring-based gravimeters, such as portable Scintrex CG5 and CG6 models, enable us to map and model gravity differences throughout the laboratory's 40 m³ volume. A superconducting relative gravimeter iGrav, allows continuous monitoring of temporal changes of g. The absolute reference value is provided by the atomic gravimeter CAG [3], which calibrates the iGrav’s scale factor [4] and evaluates its drift.

The laboratory's size facilitates the simultaneous accommodation of several gravimeters, enabling regular comparison campaigns. The first comparison in 2006 involved only absolute gravimeters of the FG5 type, while recent comparisons have also included atomic gravimeters like AQGs [5]. The site is routinely used to assess the performance and verify the functionality of the French national gravimeter park (PIN PGravi) [6], particularly before participating in international comparisons with FG5 (#206 and #228) [7] and AQG-B01 [8].

This open-access reference site allows users to verify their instruments before field missions, calibrate spring-based relative gravimeters such as the gPhoneX, and test new developments, including quantum gravimeter and dual gravi-gradio-meter systems.

[1] https://qu-test.eu

[2] M. Thomas et al (2017) metrologia 54

[3] R. Karcher et al (2018) New J. Phys 20

[4] S. Merlet et al (2021) J Geod 95

[5] V. Ménoret et al (2018) Sci Rep 8

[6] S. Merlet et al (2024) IEEE Instrum Meas Mag 27

[7] H. Wziontek et al (2025) G4.2 EGU

[8] S. Merlet et al (2025) G4.2 EGU

How to cite: Addi, N., Pereira Dos Santos, F., and Merlet, S.: Gravimetry platform for evaluation and characterization of quantum technologies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17252, https://doi.org/10.5194/egusphere-egu25-17252, 2025.

The CARIOQA (Cold Atom Rubidium Interferometer in Orbit for Quantum) project aims for the preparation of a pathfinder mission with an atom interferometric accelerometer for a deployment in future missions for earth observation. Atom interferometers offers drift-free, long-term stable measurements, complementing established technology, and consequently the expectation of improved data recovery at low frequencies.

To date, comer cialisation of atom interferometers is ongoing, they were deployed on mobile platforms, and atom optics payloads were adapted to and operated on a zero-g plane, a drop tower, sounding rockets, and a space station. The next step would be embarking such a system on a dedicated satellite to verify its functionality, the goal of CARIOQA.

The project is currently being worked on in two parts, the Pathfinder Mission Preparation (PMP) and the Phase A (PHA). The focus of PMP is on the development of an engineering model of the quantum accelerometer accompanied by the scientific background and considerations for the operation in orbit. PHA is investigating the feasibility of a quantum space gravimetry pathfinder mission within the next decade.

This contribution will outline the background and introduce the CARIOQA project.

CARIOQA is a joint European project, funded by the European Union, including experts in satellite instrument development (Airbus, Exail SAS, TELETEL, LEONARDO), quantum sensing (LUH, SYRTE, LP2N, LCAR, ONERA, FORTH), space geodesy, Earth sciences and users of gravity field data (LUH, TUM, POLIMI, DTU), mission analysis (GMV) as well as in impact maximisation and assessment (PRAXI Network/FORTH, G.A.C. Group), coordinated by the French and German space agencies CNES and DLR under CNES lead.

How to cite: Biskupek, L. and the CARIOQA Consortium: The CARIOQA Project - A Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19523, https://doi.org/10.5194/egusphere-egu25-19523, 2025.

For over two decades, satellite gravimetry missions have been measuring the Earth’s gravity field globally providing valuable observations for geosciences. Successor missions are already in development to extend this time series. Future objectives include achieving higher spatial and temporal resolutions of gravity field products as well as enhancing the measurement accuracy, currently constraint by, among other aspects, instrument performances. While some adaptations have already been made or are foreseen for the upcoming MAGIC constellation, a significant advancement could be made by replacing or combining the commonly used electrostatic accelerometer on board the satellites with quantum-based sensors to overcome currently existing limitations.

Before launching a dedicated quantum space gravimetry mission, however, the application of a cold atom interferometer as an accelerometer in space needs to be demonstrated to reach the necessary technology readiness level. This shall be achieved by a quantum pathfinder mission which is prepared in the framework of the Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometer (CARIOQA) project in the Horizon Europe funding programme. The ongoing Pathfinder Mission Preparation (CARIOQA-PMP) project involves developing an engineering model as well as a comprehensive study on the potential scientific outcome of both the quantum pathfinder mission and a future quantum space gravimetry mission. In parallel to PMP, a Phase A (CARIOQA-PHA) study defining requirements on the mission, instrument and satellite, and assessing the overall feasibility of a quantum space gravimetry pathfinder mission is nearing its completion.

This contribution will present simulated gravity field solutions considering the CARIOQA pathfinder mission, a single satellite in high-low satellite-to-satellite tracking mode, and possible future quantum space gravimetry missions consisting of a satellite constellation utilizing low-low satellite-to-satellite tracking. Closed-loop simulations were carried out to assess the benefits of a quantum-based accelerometer compared to the commonly used electrostatic one and to identify remaining challenges.

CARIOQA-PMP is a joint European project, including experts in satellite instrument development (Airbus, Exail SAS, TELETEL, LEONARDO), quantum sensing (LUH, SYRTE, LP2N, LCAR, ONERA, FORTH), space geodesy, Earth sciences and users of gravity field data (LUH, TUM, POLIMI, DTU), as well as in impact maximisation and assessment (PRAXI Network/FORTH, G.A.C. Group), coordinated by the French and German space agencies CNES and DLR under CNES lead. The CARIOQA-PHA project includes key partners (CNES, DLR, ADS-F, ADS-G, FORTH) from the CARIOQA-PMP consortium, plus a new industrial partner for the mission analysis (GMV).

We acknowledge the funding by the European Union for the projects CARIOQA-PMP (Project-ID 101081775) and CARIOQA-PHA (Project-ID 101135075).

How to cite: Fletling, N., Knabe, A., Müller, J., Schilling, M., Biskupek, L., and Weigelt, M.: CARIOQA Pathfinder Mission Development towards Future Quantum Space Gravimetry Missions , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17732, https://doi.org/10.5194/egusphere-egu25-17732, 2025.

The Cold Atom Rubidium Interferometer in Orbit for Quantum Accelerometry - Pathfinder Mission Preparation project (CARIOQA-PMP) is funded under the EU HORIZON program with the aim of developing quantum accelerometers for space applications. Such technology will be used for satellite-based Earth science to support monitoring climate change and the development of mitigation and adaption measures.

The aim of the current work is to assess the expected gravity field recovery performance of the CARIOQA pathfinder mission by running end-to-end simulations based on possible mission configurations. The satellite will be equipped with a single-arm quantum accelerometer and a GNSS receiver. Orbital parameters and instrumental error models are provided by the technological partners of the project. In particular, three orbital scenarios are considered (circular, elliptical and variable-altitude orbits) and a CAI accelerometer with 10^-10 m/s² accuracy level is assumed.

The simulations are performed by applying the space-wise approach developed at POLIMI. The results show that the CARIOQA pathfinder mission is promising for the estimation of the very low degrees of the time variable gravity field, thanks to the almost flat error power spectral density of the cold atom interferometer.

How to cite: Rossi, L., Reguzzoni, M., Eslami, A. M., Batsukh, K., and Migliaccio, F.: CARIOQA-PMP: preliminary results of gravity field recovery simulations for the pathfinder mission by the space-wise approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17773, https://doi.org/10.5194/egusphere-egu25-17773, 2025.