On thermospheric neutral density and wind estimation

The neutral mass density of the upper thermosphere can be determined by orbit and accelerometer data from Low Earth Orbit (LEO) satellites. Especially the accelerometers of geodetic satellites, measuring the non-gravitational accelerations acting on these satellites, are a very useful observation for precise density estimation also on very short time scales.

In this contribution we present our density and wind estimation approach with focus on the wind estimation. In the accelerometer data differences to modelled non-gravitational accelerations persist, which are only attributable to aerodynamic accelerations due to an additional wind, especially for high solar activity. Utilizing a thermospheric wind model like HWM14 reduces the differences slightly, but by far not sufficiently. Hence, for a long time (e.g. by TU Delft) efforts have been made to estimate not only density but also winds. We show the potential and problems of the wind estimation with different approaches, and the influence on the alongside estimated neutral density. We use the GRACE mission, which, gives the opportunity to compare results from both GRACE satellites, being on the same orbit with a distance of only about 200 km, by time-shifting the data from the position of the one to the other satellite. Furthermore, we compare our results with data from TU Delft.

Our density datasets and lots of auxiliary data for GRACE/-FO are available on our data server: www.zarm.uni-bremen.de/zarm_daten