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Datum: 15.02.2022

Scale Factors of the Thermospheric Density: A Comparison of Satellite Laser Ranging and Accelerometer Solutions.

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A major problem in the precise orbit determination (POD) of satellites at altitudes below 1,000 km is the modelling of atmospheric drag, which depends mainly on thermospheric density and causes the largest non-gravitational acceleration. Normally, thermospheric densities at satellite positions are determined by empirical models, which have limited accuracy. But conversely, satellites orbiting the Earth within the thermosphere can be used to derive thermospheric density information because of their sensitivity to perturbing accelerations.


Time series of scale factors

Time series of scale factors of the modelled thermospheric density, derived from different laser ranging satellites and from Emmert et al. 2021 [offset by a constant, for clarity]. (© Graphic: Zeitler et al. 2021, Journal of Geophysical Research - Space Physics)


Scientists from DGFI-TUM and the Institute of Geodesy and Geoinformation at the University of Bonn (IGG Bonn) have for the first time compared thermospheric density corrections in the form of scale factors for the NRLMSISE-00 model with a temporal resolution of 12 hours. It was shown that time-averaged scale factors from in-situ acceleration measurements on board CHAMP and GRACE fit well to arc-wise scale factors from the Satellite Laser Ranging (SLR) technique applied to the spherical satellites Larets, Stella, WESTPAC and Starlette.

The estimated scale factors vary by up to 30% around the value of 1 at low solar activity and by up to 70% at high solar activity. This shows the extent to which the NRLMSISE-00 model values of thermospheric density deviate from the observed values. On average, at low solar activity the model overestimates the thermospheric density and has to be scaled down with the estimated scale factors, while at high solar activity the model underestimates the density values and has to be scaled up.

Depending on the altitude, there are correlations of up to 0.8 between the scale factors derived from accelerometer data and those estimated from SLR. To check the reliability of the latter, the POD results from two different software packages were compared, namely DOGS-OC at DGFI-TUM and GROOPS at IGG Bonn. Above 680 km altitude, a linear decrease in the estimated thermospheric density scale factors of about -5% per decade was observed, possibly related to climate change. The results of this study are published in the article "Scale Factors of the Thermospheric Density: A Comparison of Satellite Laser Ranging and Accelerometer Solutions".


... to publication: | 05.12.2021