The dynamics of satellite orbits are determined by conservative (gravitational field) and non-conservative (e.g. due to atmospheric drag or solar radiation pressure) forces. All forces are modelled and parameterised in our central “Earth Parameter and Orbit System” software package EPOS. By evaluating observations such as “Doppler Orbitography and Radiopositioning Integrated by Satellite” (DORIS), “Global Navigation Satellite System” (GNSS), “Satellite Laser Ranging” (SLR) and other techniques such as inter-satellite distance measurements on GRACE or GRACE-FO, EPOS allows us to calculate all our parameters of interest with highest accuracy in the sense of a least squares adjustment and at the same time obtain highly precise satellite orbits.
We provide our results to the IAG services “International Earth Rotation and Reference Systems Service” (IERS), “International Laser Ranging Service” (ILRS) and “International DORIS Service” (IDS) and make the calculated satellite orbits available to the scientific community via the GFZ ISDC. At the same time, we also offer our precise satellite orbits or inter-satellite baselines to various project partners such as GMV, ESA or DLR as part of third-party funded projects. Since EPOS also has a simulation mode, we can investigate the effects of future instrumentation on geodetic target parameters on various satellite missions planned by ESA (e.g. Next Generation Galileo or GENESIS).
Of particular interest to us is the method of distance measurement using satellite laser radar (SLR). We regularly provide various products as an official SLR Analysis Center for the International Laser Ranging Service (ILRS) and thus also contribute to the development of new international coordinate systems such as the “International Terrestrial Reference Frame” (ITRF). Additionally, we operate a SLR station on the Telegraph Hill as part of the worldwide station network of the ILRS.
Similar to the ILRS Analysis Centre, we have also been operating an Associated Analysis Centre for the International Doris Service (IDS) since several years. To analyse GNSS radio occultation data for the improvement of weather forecasts for various European weather services, we have been operating an operational 24/7 Rapid Science (RSO) and Near Realtime Orbit (NRT) orbit determination for Low Earth Orbiters (LEO) such as CHAMP, GRACE, GRACE-FO, TerraSAR-X or TanDEM-X since 2000.
For these and various other LEOs, we also calculate orbit predictions, which contribute significantly to the success of these missions, as they are the basis for planning the download of satellite data (e.g. with the help of our satellite receiving station in Ny-Ålesund) or for controlling instruments on satellites. The most demanding application is the control of the SLR ground stations of the ILRS. This requires an accuracy of approximately 70 metres in the orbit direction, which corresponds to a deviation of 10 ms from the time at which the satellite becomes visible above a station (i.e. the satellite is too early or too late). The accuracy of the predicted orbits is constantly monitored and compared, for example, with the RSOs mentioned above, which serve as highly accurate (a few centimetres) reference orbits.
The Lense-Thirring effect, which describes the precession of the orbital node of a particle flying around a rotating mass and which is a manifestation of the phenomenon of general relativity, was measured by us from the node drifts of the LAGEOS and LARES satellites using the GRACE gravity fields with an accuracy of approx. 10%.
In addition to these topics, we are working on a number of third-party funded projects, e.g. by
- using our SLR station to participate in long-distance time transfer experiments,
- investigating the benefits of future global navigation satellite systems (NextGNSS), which will be a further development of the current GPS, GLONASS, Galileo or Beidou constellations, in order to better achieve some important goals of the Global Geodetic Observing System (GGOS),
- routinely calculating high-precision orbits for the Sentinel satellites of the Copernicus Earth observation programme of the European Commission and the European Space Agency (ESA), or
- routinely performing high-precision baseline determination between the two radar satellites TanDEM-X and TerraSAR-X on behalf of DLR.
Literature
Below you find some recent publications of the working group 3. The section's complete list of publications can be found here.
Neumayer, K. H., Schreiner, P. A., König, R., Dahle, C., Glaser, S., Mammadaliyev, N., Flechtner, F. (2024 online): EPOS-OC, a Universal Software Tool for Satellite Geodesy at GFZ. - In: (International Association of Geodesy Symposia), Berlin, Heidelberg: Springer.
https://doi.org/10.1007/1345_2024_260
Schreiner, P. A., König, R., Neumayer, K., Reinhold, A. (2023): On precise orbit determination based on DORIS, GPS and SLR using Sentinel-3A/B and -6A and subsequent reference frame determination based on DORIS-only. - Advances in Space Research, 72, 1, 47-64.
https://doi.org/10.1016/j.asr.2023.04.002
Testa, A., Michalak, G., Dassie, M., Neumayer, K., Giorgi, G. (2023): Estimating Satellite Navigation Broadcast Ephemeris via Inter-Satellite and Ground-to-Satellite Ranging. - Engineering proceedings, 54, 1, 15.
https://doi.org/10.3390/ENC2023-15463
König, R., Reinhold, A., Dobslaw, H., Esselborn, S., Neumayer, K., Dill, R., Michalak, A. (2021): On the effect of non-tidal atmospheric and oceanic loading on the orbits of the altimetry satellites ENVISAT, Jason-1 and Jason-2. - Advances in Space Research, 68, 2, 1048-1058.
https://doi.org/10.1016/j.asr.2020.05.047
Glaser, S., Michalak, G., Männel, B., König, R., Neumayer, K., Schuh, H. (2020): Reference system origin and scale realization within the future GNSS constellation "Kepler". - Journal of Geodesy, 94, 117.
https://doi.org/10.1007/s00190-020-01441-0
Glaser, S., König, R., Neumayer, K., Balidakis, K., Schuh, H. (2019): Future SLR station networks in the framework of simulated multi-technique terrestrial reference frames. - Journal of Geodesy, 93, 11, 2275-2291.
https://doi.org/10.1007/s00190-019-01256-8
Glaser, S., König, R., Neumayer, K., Nilsson, T., Heinkelmann, R., Flechtner, F., Schuh, H. (2019): On the impact of local ties on the datum realization of global terrestrial reference frames. - Journal of Geodesy, 93, 5, 655-667.
https://doi.org/10.1007/s00190-018-1189-0