TIRO - Topside Ionosphere Radio Observations from multiple LEO-missions

Instrumentation carried on LEO (Low Earth Orbit) satellites are indispensable to seek information on the electron content of the upper atmosphere. Knowledge on electron density variations is crucial to investigate the ionospheric effect on radio communication and navigation signals, such as GNSS, to mitigate these effects. TIRO deals with the derivation of two measures onboard LEO satellites, e.g., TEC (Total Electron Content derived from GNSS signals) and electron density derived from KBR (K-Band Ranging) system observations.

The Swarm mission provides time series of TEC for each of the 3 satellites as a daily product on an operational basis. The main goal of TIRO is to extend the existing data set with other high-quality topside TEC products derived from LEO missions CHAMP, GRACE, and GRACE-FO. TIRO aims at the inter-comparability of data from different missions by using a common TEC processor optimized for LEO receivers.

Another goal of TIRO is to extend the existing Swarm data sets for in situ plasma density by adding similar products derived from inter-satellite K-band radio links between the two GRACE and GRACE-FO satellites, respectively.

The benefit of combining observations from multiple satellites is to enhance the spatial and local time coverage of ionospheric sounding. At the completion of TIRO electron content and density data of the topside ionosphere will be available for nearly two solar cycles from 2000 up to present (see figure above). Swarm and GOCE TEC data are available at http://swarm-diss.eo.esa.int and http://eo-virtual-archive1.esa.int, respectively.

Time Frame

Aug 2020 – Feb 2022


The European Space Agency (ESA) through Technical University of Denmark (DTU) - ITT 3.3 Extending Swarm TEC products with data from other LEO satellite

Principal Investigators



  • Faculty of Aerospace Engineering of Delft University of Technology (TU Delft)
  • Astronomical Institute of the University of Bern (AIUB)

Selected Related Publications and Documents

  • Xiong, C., Xu, J.‐S., Stolle, C., van den Ijssel, J., Yin, F., Kervalishvili, G. N., and Zangerl, F. (2020), On the occurrence of GPS signal amplitude degradation for receivers on board LEO satellites. Space Weather, 18, e2019SW002398, doi: 10.1029/2019SW002398.
  • Schreiter, L., Stolle, C., Arnold, D., and Jäggi, A. (2020), Altitude dependent empirical modeling of the topside ionosphere and plasmasphere using GPS- TEC from Swarm, GRACE-FO and the Sentinel satellites, EGU2020-4809, doi: 10.5194/egusphere-egu2020-4809.
  • Noja, M., Stolle, C., Park, J., and Lühr, H. (2013), Long‐term analysis of ionospheric polar patches based on CHAMP TEC data, Radio Sci., 48, 289– 301, doi: 10.1002/rds.20033.
  • Xiong, C., Park, J., Lühr, H., Stolle, C., and Ma, S. Y. (2010), Comparing plasma bubble occurrence rates at CHAMP and GRACE altitudes during high and low solar activity, Annales Geophysicae, 28, 1647–1658, doi: 10.5194/angeo-28-1647-2010.
  • GO-TN-HPF-GS-0337, GOCE TEC and ROTI validation report
  • SW-TR-GFZ-GS-0007, Swarm Level 2 TEC Product Description