G4.1

G4

Recent developments in quantum physics has enabled novel applications and measurement concepts in geodesy and Earth‘s gravitational field observation. In this Session, we discuss new types of sensors and gravity mission concepts that require the application of the advanced techniques. We will address the measurement of the terrestrial gravity anomalies by means of observing free-falling atoms (quantum gravimetry) which is gradually replacing the falling corner cubes. Atom interferometry allows nearly continuous measurements and offers the access to gradients. It is also supposed for future gradiometric measurements in space.
According to Einstein’s theory of general relativity, frequency comparisons of highly precise optical clocks connected by optical links give a direct access to differences of the gravity potential (relativistic geodesy) which allows gravity field recovery and height determination on long baselines. In future, precise optical clocks can be applied for defining and realizing an international height system in a new way, and moreover, help to improve the accuracy of the International Atomic Time scale TAI. Optical clocks are important for all space geodetic techniques as well as for the realization of reference systems.
Additionally, laser interferometry between test masses in space with nanometer accuracy – which has been realized as a demonstrator in the GRACE-FO mission – also belongs to these novel concepts, and in the future even more refined concepts (tracking swarms of satellites, space gradiometry) will be realized.
Finally, changes in the gravity field can be derived from GNSS displacement values which play an increasingly important role due to the relatively cheap and easy deployment of GNSS receivers and the large number of stations.
All these above-mentioned techniques will open a door to a vast bundle of applications such as fast local gravimetric surveys, the gravimetric observation of the Earth-Moon system with high spatial-temporal resolution. Terrestrial mass variations can be monitored at various scales providing unique information on the climate change processes.
We invite presentations illustrating the principles and state of the art of those novel techniques and the application of the new methods for terrestrial and satellite geodesy, navigation and fundamental physics. We also welcome papers covering theoretical foundations and description of the new methods as well as revised modeling schemes.

Convener: Jürgen Müller | Co-conveners: Sergei Kopeikin, Sébastien MerletECSECS, Munawar ShahECSECS, Wenbin Shen
Presentations
| Thu, 26 May, 13:20–15:54 (CEST)
 
Room -2.16

Presentations: Thu, 26 May | Room -2.16

Chairpersons: Jürgen Müller, Sébastien Merlet, Wenbin Shen
Advanced Space Gravimetry
13:20–13:26
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EGU22-6448
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On-site presentation
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Vitali Müller, Laura Müller, Malte Misfeldt, Henry Wegener, Markus Hauk, Gerhard Heinzel, Kai Voss, and Kolja Nicklaus

The Laser Ranging Interferometer (LRI) onboard the GRACE Follow-On mission is operational for almost four years. It provides high-quality ranging data with a noise below 1 nm/√Hz at Fourier frequencies around 1 Hz, as well as attitude information with respect to the line-of-sight between the two spacecraft. Future missions are being developed by ESA under the name Next Generation Gravity Mission (NGGM) and on US-side as so-called Mass Change Mission (MCM), and in a joint frame as Mass Change and Geosciences International Constellation (MAGIC).

In this presentation, we discuss the basic working principle of the LRI and show some advantages of the design. The low ranging noise below 35 mHz Fourier frequency allows to retrieve finer structures of Earth’s gravity field than possible with conventional microwave ranging. In contrast, the low fluctuations at higher frequencies are useful to characterize the satellite platforms, e.g., thrusters and impulse-like non-gravitational accelerations, potentially from impacts of micrometeorites. We address the learned lessons from the instrument so far and sketch the challenges and development efforts ongoing for the upcoming missions.

How to cite: Müller, V., Müller, L., Misfeldt, M., Wegener, H., Hauk, M., Heinzel, G., Voss, K., and Nicklaus, K.: Laser Ranging Interferometers in GRACE-FO and for NGGM - Status, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6448, https://doi.org/10.5194/egusphere-egu22-6448, 2022.

13:26–13:32
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EGU22-3208
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ECS
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Virtual presentation
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Hussein A. Mohasseb, Hussein A. Abd-Elmotaal, and WenBin Shen

Using time-variable gravity field models has recently become essential for studying the hydrology change, ice melting, Earth’s crust deformation, etc. One of the most successful missions for establishing the time-variable gravity field model is the Gravity Recovery and Climate Experiment (GRACE) mission and its successor GRACE-Follow On (GARCE-FO) mission. However, the eleven-month gap between the end of GRACE's life span and the start of GRACE-FO observations hinders the study continuation. This investigation is devoted to model the GRACE data using time-variable gravity field model employing a smart least-squares regression technique. The GRACE-derived time-variable gravity field model is validated first using available GRACE data used in the modeling technique (to measure the internal precision of the model) as well as using available GRACE data which have not been used in the modeling technique (to measure the external accuracy of the model). The assessment of the derived model has been carried out at two different levels in the frequency domain (through the harmonic coefficients and the degree variances) and in the space domains (through the total water storage change in Africa). The GRACE-derived time-variable gravity field model has then been used to fill in the GRACE/GRACE-FO gap. A comparison among the existing techniques of filling-in the GRACE gaps versus the derived technique within the current investigation is given and widely discussed. This study is supported by the National Natural Science Foundations of China (NSFC) under Grants 41874023, 41721003, 41631072.

Keywords: GRACE, GRACE-FO, Gravity, GRACE gap, TWS, Least square adjustment. 

How to cite: Mohasseb, H. A., Abd-Elmotaal, H. A., and Shen, W.: Filling GRACE Gaps Using GRACE-Derived Time Varying Model  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3208, https://doi.org/10.5194/egusphere-egu22-3208, 2022.

13:32–13:38
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EGU22-1168
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ECS
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On-site presentation
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Arthur Reis, Alexey Kupriyanov, and Vitali Müller

    Accelerometers are integral part of the science instrument payloads of space based gravimetry and gravitational wave measurements. These are either used to detect the actuating forces on the body of the spacecraft, to enable a drag-free scenario where a test mass will follow a geodesic, or combined in pairs as to build a gradiometer. From a technological standpoint, different techniques have been used to measure the acceleration, from capacitance reading, to optical interferometry, to cold atom interferometry. As the next generation gravimetry missions are considered, there is a need to assist the design of this instrument, preferentially without having to recreate a model for each family of devices within the same framework, in order to simulate its performance and to enable the best science return.
    
    Here is presented a tool to model and simulate accelerometers. This comprises a Simulink library containing the components and their associated Matlab scripts. It is being developed to be modular, parametric, agnostic in respect of measurement technique, flexible in the mode of operation of the instrument, and instantiable to accommodate scenarios with multiple accelerometers on one or more spacecrafts. This tool can run as a standalone simulation, with multiple arbitrary generated noise inputs to obtain the overall noise budget and also can be integrated with XHPS, a Simulink library that simulates satellite dynamics with high precision gravity field models, to calculate the in-flight instrument sensitivity.

How to cite: Reis, A., Kupriyanov, A., and Müller, V.: A Tool for  Accelerometer Modeling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1168, https://doi.org/10.5194/egusphere-egu22-1168, 2022.

13:38–13:44
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EGU22-2023
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ECS
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On-site presentation
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Alexey Kupriyanov, Arthur Reis, Manuel Schilling, Vitali Müller, and Jürgen Müller

Electrostatic accelerometers (EA) are one of the limiting factors of space gravimetry missions dominating the error contribution at low frequencies (<10−3Hz). The focus of this study is on the modelling of an optical accelerometer that can improve gravity field retrieval to unprecedented accuracy. Contrary to GRACE(-FO) or GOCE accelerometers, optical accelerometers sense the motion of the test mass (TM) in one or more axes by applying laser interferometry. Combination of sensing in multiple directions and of several test masses would lead to enhanced gradiometry which would improve the determination of the static gravity field to a higher spatial resolution. Modelling of the above-mentioned accelerometer blocks in Matlab Simulink allows to simulate various TM measurement scenarios for satellite missions under different conditions, e.g. dedicated satellite configurations, various non-gravitational forces, etc. This research is based on very promising results of the mission LISA-Pathfinder (LPF) which has demonstrated the benefit of a drag-free system in combination with optical accelerometry that allowed sensing of non-gravitational accelerations several orders of magnitude more accurate than those of current gravity missions like GRACE-FO. This research project is carried out in close collaboration with the IGP and the DLR-SI, to provide - on the long run - a roadmap for improved angular and linear accelerometry for the next generation of gravity field missions.

In this presentation, we now introduce a functional model of 6 degrees-of-freedom (DoF) optical accelerometer and compare its output with the measurements of electrostatic accelerometers for the dual satellite configuration, i.e. GRACE-FO mission. Also, the current state of the Simulink implementation of the accelerometer model which are mainly developed by IGP are presented. Finally, the simulated gravity gradients from the novel gradiometer based on the optical accelerometers are demonstrated as well as benefits that can be acquired from this sensor.

This project is funded by: Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Project-ID 434617780 – SFB 1464.

How to cite: Kupriyanov, A., Reis, A., Schilling, M., Müller, V., and Müller, J.: Sensor and performance modelling of an optical accelerometer for future gravity field missions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2023, https://doi.org/10.5194/egusphere-egu22-2023, 2022.