An accurate estimation of Thermospheric Neutral Density (TND) is important for designing the Low-Earth-Orbit (LEO) missions mainly those with the altitude of less than 1000 km. It is also essential, for example, to predict satellite missions’ life-time, planning their required on-board fuel, performing reliable attitude control, designing orbital manoeuvre, as well as predicting and performing Earth re-entry.
Predicting the thermosphere-ionosphere system is challenging because it is highly influenced by the solar irradiance, and it depends on the state of the neutral temperature and composition. External forces such as those related to the space weather events, as well as interactions between neutral molecules with charged particles considerably influence the thermopsheric variability. Empirical thermosphere or coupled thermosphere-ionosphere models are common tools to provide an estimation of TND (e.g., for drag computations), however, their accuracy is limited due to simplification of model structure, coarse sampling of model inputs, and the model’s dependencies on the calibration period.
Satellite geodetic missions such as the Challenging Minisatellite Payload (CHAMP, 2000-2010), the Gravity Recovery and Climate Experiment (GRACE, 2002-2017) and its Follow-On mission (GRACE-FO, launched in 2018), Gravity field and steady-state Ocean Circulation Explorer (GOCE, 2009-2013), and the European Space Agency (ESA)’s Swarm mission (Swarm-A, -B, and -C launched in 2013) are equipped with accelerometer sensor to measure non-gravitational forces acting on their surface. The dominant portion of these forces is due to the atmospheric drag, which can be used to estimate TNDs along track of satellites with very high temporal rates.
Our research group works on:
1) Processing of the accelerometer observations of CHAMP, GRACE, GOCE, GRACE-FO, and Swarm on-board accelerometer measurements (or from their dynamic orbits), see e.g., Vielberg et al. (2018 and 2021);
2) Integrating the satellite-derived TND data with available models through generating empirical corrections (e.g., Forootan et al., 2019) and simultaneous Calibration and Data Assimilation (C/DA), see e.g., Forootan et al. (2021, 2022);
3) Studying the Data Assimilation frameworks for coupled atmosphere-ionosphere models. The group has experiences with running upper atmosphere models such MSISE, NRMLMSISE, JB08, DTM, and TIEGCM.
Our recent studies on the application of C/DA to generate global multi-level TND fields have provided promising results that show this technique is efficient for predicting thermospheric variables. A comprehensive study including seven events with high geomagnetic activity has been performed in the context of an ESA project.
An overview of the C/DA framework to integrate space based along track accelerometer measurements into empirical thermosphere models. The assessment is done during periods with high geomagnetic activity, see details within a new report for the European Space Agency
An overview of the sampling thermospheric neutral density measurements using GRACE accelerometer sensors.
Related Publications:
E Forootan et al. “Estimating and predicting corrections for empirical thermospheric models.” In: Geophysical Journal International 218.1 (2019), pp. 479–493. doi: 10.1093/gji/ggz163.
E Forootan et al. “A simultaneous calibration and data assimilation (C/DA) to improve NRLMSISE00 using thermospheric neutral density (TND) from spaceborne accelerometer measurements.” In: Geophysical Journal International 224.2 (Oct. 2020), pp. 096–1115. doi: 10.1093/gji/ggaa507.
E Forootan et al. “Forecasting global and multi-level thermospheric neutral density and ionospheric electron content by tuning models against satellitebased accelerometer measurements.” In: Scientific Reports 12.1 (2022), pp. 1– 19. doi: 10.1038/s41598-022-05952-y.
Vielberg, K., Forootan, E., Lück, C., Löcher, A., Kusche, J., and Börger, K.: Comparison of accelerometer data calibration methods used in thermospheric neutral density estimation, Ann. Geophys., 36, 761–779, https://doi.org/10.5194/angeo-36-761-2018.
K Vielberg et al. TND-IGG RL01: Thermospheric neutral density from accelerometer measurements of GRACE, CHAMP and Swarm. data set. 2021. doi: 10.1594/PANGAEA.931347.
E Forootan (2023), ESA’s multi-level global thermosphere data products consistent with Swarm and GRACE (-FO), technical report for the European Space Agency (ESA)