Preliminary Validation of Thermosphere Observations from the TOLEOS Project

OBSERVATIONS of upper atmospheric neutral mass density (NMD) and wind are critical to understand the coupling mechanisms between Earth’s ionosphere, thermosphere, and magnetosphere. The ongoing Swarm DISC (data, innovation, and science cluster) project TOLEOS (thermosphere observations from low-Earth orbiting satellites) aims to provide better calibrated NMD and crosswind data from CHAMP, GRACE, and GRACE-FO (follow-on) satellite missions. The project uses state-of-the-art models, calibration techniques, and processing standards to improve the accuracy of these data products and ensure inter-mission consistency. Here, we present preliminary results of the quality of the data in comparison to the high accuracy drag temperature model DTM2020, and physics-based TIE-GCM (thermosphere ionosphere electrodynamics general circulation model) and CTIPe (coupled thermosphere ionosphere plasmasphere electrodynamics) models

TOLEOS: Thermosphere Observations from Low-Earth Orbiting Satellites

The objective of the TOLEOS project is to process the CHAMP, GRACE, and GRACE-FO accelerometer measurements with improved processing standards to obtain thermosphere density and crosswind data products. These new data products will cover the entirety of the accelerometer missions and complement the existing ESA databases for Swarm and GOCE. The improvements in the processing focus on the radiation pressure modelling, which is expected to have a significant effect on the density and crosswind data, in particular at altitudes above 450 km during solar minimum conditions. Substantial validation activities are performed since the project’s start in June 2021 and will continue until the end of the project in July 2022

Radiation pressure modelling for improving neutral thermosphere density and crosswind data products

Uncertainties in the radiation pressure modelling at altitudes above 450 km play a significant role in the thermosphere density and crosswind observations, especially during low solar activity conditions when the along-track radiation pressure and aerodynamic accelerations match in magnitude. The GRACE-FO mission has been operating for several years at such high altitudes during both low and rising solar activity, serving as a perfect opportunity to study the effects of radiation pressure. In our approach to solar radiation pressure modelling, we employ the high-fidelity geometry model of GRACE-FO, augmented with parameters describing the thermo-optical surface properties. We finetuned those parameters to obtain more accurate accelerations than when using the parameters specified in the mission’s handbook. We then used ray-tracing techniques on the augmented geometry models to derive the force coefficients, accounting for shadowing and multiple reflections. The thermal radiation pressure accounts for one-fifth of total cross-track radiation pressure acceleration. To calculate the thermal radiation, we use the in-situ measurements from thermistors that monitor the temperature in several locations on the outer surfaces of the GRACE-FO satellites. This gives us insight into selecting the realistic thermal model control parameters and improves the crosswind observations. Additionally, having access to the thermistors data provides valuable understanding for other missions such as CHAMP and GRACE, for which such measurements are not publicly available. In this presentation, we will show a comprehensive approach to improve the radiation pressure modelling based on the example of the GRACE-FO satellite. Furthermore, we will present enhanced and consistently processed neutral mass densities and crosswind observations for the GRACE and GRACE-FO missions, determine the impact of radiation pressure modelling errors on these datasets, and compare the results with thermosphere models, including the TIE-GCM mode

Neutral mass density data compared with physics-based model estimates

Observations of upper atmospheric neutral mass density (NMD) and wind are critical to understand the coupling mechanisms between Earth’s ionosphere, thermosphere, and magnetosphere. The Swarm DISC (data, innovation, and science cluster) project TOLEOS (thermosphere observations from low-Earth orbiting satellites) provide better calibrated NMD and crosswind data from CHAMP, GRACE, and GRACE-FO (follow-on) satellite missions. The project uses state-of-the-art models, calibration techniques, and processing standards to improve the accuracy of these data products and ensure inter-mission consistency. Here, we present preliminary results of the quality of the data in comparison to the physics-based TIE-GCM (thermosphere ionosphere electrodynamics general circulation model) model

New Thermosphere Neutral Mass Density and Crosswind Datasets from CHAMP, GRACE, and GRACE-FO

We present new neutral mass density and crosswind observations for the CHAMP, GRACE, and GRACE-FO missions, filling the last gaps in our database of accelerometer-derived thermosphere observations. For consistency, we processed the data over the entire lifetime of these missions, noting that the results for GRACE in 2011–2017 and GRACE-FO are entirely new. All accelerometer data are newly calibrated. We modeled the temperature-induced bias variations for the GRACE accelerometer data to counter the detrimental effects of the accelerometer thermal control deactivation in April 2011. Further, we developed a new radiation pressure model, which uses ray tracing to account for shadowing and multiple reflections and calculates the satellite’s thermal emissions based on the illumination history. The advances in calibration and radiation pressure modeling are essential when the radiation pressure acceleration is significant compared to the aerodynamic one above 450 km altitude during low solar activity, where the GRACE and GRACE-FO satellites spent a considerable fraction of their mission lifetime. The mean of the new density observations changes only marginally, but their standard deviation shows a substantial reduction compared to thermosphere models, up to 15% for GRACE in 2009. The mean and standard deviation of the new GRACE-FO density observations are in good agreement with the GRACE observations. The GRACE and CHAMP crosswind observations agree well with the physics-based TIE-GCM winds, particularly the polar wind patterns. The mean observed crosswind is a few tens of m · s−1 larger than the model one, which we attribute primarily to the crosswind errors being positive by the definition of the retrieval algorithm. The correlation between observed and model crosswind is about 60%, except for GRACE in 2004–2011 when the signal was too small to retrieve crosswinds reliably

TOLEOS: Thermosphere Observations from Low-Earth Orbiting Satellites

The TOLEOS project will provide new thermosphere density and crosswind observations derived from the accelerometer data of the CHAMP, GRACE, and GRACE-FO missions. The accurate calibration of the accelerometer data and the upgrade of the radiation pressure model are key elements of the project, which is funded by the Swarm Data, Innovation, and Science Cluster (Swarm DISC). To improve the radiation pressure modelling, we use ray tracing techniques in combination with high-fidelity geometry models of the satellites, which were augmented with the thermo-optical properties of the surfaces. This substantially reduces the uncertainty stemming from the satellite geometry modelling and shadowing effects. In addition, we introduce thermal models of the satellites to account for the radiation of heat from the satellites themselves. We will elaborate the accelerometer data calibration and briefly explain the upgraded radiation pressure modelling. Further, we will compare the new thermosphere density and crosswind observations to the existing observations to the highlight the differences and demonstrate the effects of the upgraded processing