The motion of a satellite depends on gravitational and non-gravitational accelerations. A major problem in the precise orbit determination (POD) of low earth orbiting (LEO) satellites is modelling the non-gravitational perturbations. Among them, the atmospheric drag acceleration – mainly depending on the thermospheric density – is largest for LEOs with altitudes lower than 1000 km. In case of the Swarm A and C satellites with an altitude of around 460 km, the non-consideration of the drag deceleration would cause an integration error in along-track of around 3 m per revolution. Consequently, the knowledge of the thermospheric density is of crucial importance for a LEO-POD.
In many geoscientific applications, e.g., remote sensing, satellite altimetry and satellite gravity missions, the orbits of LEO satellites should be known with a sub-centimeter accuracy. As an example, the Figure above shows the global distribution of the thermospheric density at March 18, 2015, the day after the St. Patrick’s day, at 10:00 UT. The impact of a geomagnetic storm on the thermosphere is usually several hours later than for the ionosphere. This delay is caused by the coupling processes. In this figure the thermospheric density is computed from the empirical model NRLMSISE-00.