G4.1

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.

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.

    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.