A comparison of scale factors for the thermospheric density from Satellite Laser Ranging and Accelerometer Measurements to LEO satellites

A major problem in the precise orbit determination of Low-Earth-Orbiting (LEO) satellites at altitudes below 1000 km is the modeling of the aerodynamic drag which mainly depends on the thermospheric density and causes the largest non-gravitational acceleration. Typically, empirical thermosphere models such as NRLMSISE-00, JB2008 or DTM2013 are used to calculate density values at satellite positions. However, since the current thermosphere models cannot provide the required accuracy, unaccounted variations in the thermospheric density may lead to significantly incorrect satellite positions.

At EGU 2021, we presented a study comparing thermospheric density corrections for the NRLMSISE-00 model in terms of scale factors calculated from satellite laser ranging (SLR) measurements to various  spherical LEO satellites (Starlette, Stella, Larets, etc.) with the corresponding values from accelerometer measurements on-board CHAMP and GRACE. In the meantime we significantly extended our study and published the results (Zeitler et al. 2021).

Our results demonstrate that both measurement techniques can be used to derive comparable (with correlations of up to 80% and more depending on altitude) scale factors of the thermospheric density with a temporal resolution of 12 hours, which vary around the value 1. This indicates to which extent the NRLMSISE-00 model differs from the observed thermospheric density. On average, during high solar activity, the model underestimates the thermospheric density and should be scaled up using the estimated scale factors. We find our estimated scale factors close to the results from Emmert et al. (2021); except for the most recent period where a different trend is observed. We also find a linear decrease of the estimated thermospheric density scale factors above 680 km of about −5% per decade due to climate change. This fits well to the results from Solomon et al. (2015). Furthermore, we validate the approach of deriving scale factors from SLR measurements by using two independent software packages.

Emmert, J. T., Dhadly, M. S., & Segerman, A. M. (2021). A Globally Averaged Thermospheric Density Data Set Derived From Two-Line Orbital Element Sets and Special Perturbations State Vectors. Journal of Geophysical Research: Space Physics, 126 (8), e2021JA029455. doi: 10.1029/2021JA029455

Solomon, S. C., Qian, L., & Roble, R. G. (2015). New 3-D simulations of climate change in the thermosphere. Journal of Geophysical Research: Space Physics, 120 (3), 2183–2193. doi: 10.1002/2014JA020886

Zeitler L., Corbin A., Vielberg K., Rudenko S., Löcher A., Bloßfeld M., Schmidt M., & Kusche J. (2021). Scale factors of the thermospheric density ‐ a comparison of SLR and accelerometer solutions. Journal of Geophysical Research: Space Physics, 126, e2021JA029708. doi: 10.1029/2021JA029708