Speaker
Description
This thesis explores how space weather affects the orbits of Earth satellites. In particular, how changes in geomagnetic activity disturb satellite paths in any possible way, including atmospheric density, and solar radiation, but also Lorentz force perturbation. The study compares satellites at very different orbital heights: CHAMP in low-Earth orbit, MetOp-A in mid-Earth orbit, the geodetic satellite Etalon-1, and the ocean altimetry mission TOPEX/Poseidon. By combining accurate orbit data with indices that describe space weather conditions, the work shows how satellites at different altitudes react both to short, intense geomagnetic storms and to long-term changes in solar activity.
The research uses time series and signal processing techniques, such as Empirical Mode Decomposition (EMD) and its improved version CEEMDAN, which are applied to orbital data. These methods make it possible to separate storm-related disturbances from long-term orbital trends. The extracted signals are then compared with geomagnetic indices like SYM-H to see how closely orbital changes follow storm activity and whether there are time delays. Secondly, orbits are simulated using the Orekit orbital toolkit, which models both gravitational and non-gravitational forces acting on them. This is done to filter the expected influences of non-space weather perturbations.
Three main conclusions are drawn. First, low-orbiting satellites act as sensitive detectors of space weather, since their orbits clearly show storm-driven decay. Second, the type of disturbance depends strongly on altitude: below 600 km, atmospheric drag dominates, while above 800 km, radiation and electromagnetic effects become more important. Thirdly, combining signal decomposition with orbit propagation is a reliable way to separate overlapping effects and measure their contributions.
