DGFI-TUM - Ionosphere

Ionosphere

In the ionosphere the solar radiation stimulates ionization processes for the production of ions and electrons from different (neutral) chemical elements, e.g. oxygen, hydrogen and nitrogen. Due to the recombination and the composition, the vertical distribution of the electron density is not equal but shows a clear maximum at about 300 to 350 km altitude. The lower ionosphere is dominated by photochemical processes; the mid ionosphere is a region in which ionization and recombination processes together with thermal and dynamic processes play important roles; the upper ionosphere is mainly influenced by transport processes that determine the vertical and horizontal distribution of the electrons. Temporal variations are dominated by daily changes, but also seasonal and long-term (mainly due to the 11-year solar cycle) effects are present.

Measurements used in various geodetic applications such as satellite-based positioning and navigation are disturbed by the ionosphere. This frequency-dependent effect acts in a twofold way: the signal travel time is delayed and the signal path is bent. Whereas the latter effect can be neglected for most applications the delay depends on the integral of the electron density along the signal path between the transmitter and the receiver. In GNSS applications the satellites are equipped with the transmitter, the receivers are either located at terrestrial observation sites or on board of LEO satellites. The integration of the electron density along the ray path defines the so-called slant total electron content (STEC). For signals in zenith direction the vertical total electron content (VTEC) is defined. It can also be obtained from STEC by applying an elevation-angle-dependent mapping function, e.g. based on the so-called single-layer approach.

Figure 1 gives an overview about the most relevant space-geodetic satellite observation techniques for modelling the two target functions of the ionosphere, namely (1) the electron density and (2) VTEC either as a functional of the electron density or as the mapping of STEC. Exemplarily, Figure 2 shows animations of the two target parameters.

Figure 2 left: Animation of DGFI-TUM’s global VTEC model for 5 consecutive days; right: representation of the electron density at heights between 100 km and 900 km for the fixed time epoch of 14:00 UT at an arbitrary day. The maps clearly illustrate the equatorial anomaly moving along the geomagnetic equator as the most dominant global phenomenon within the ionosphere.

Related Projects

Selected Publications

Erdogan E., Schmidt M., Goss A., Görres B., Seitz F.: Real‐time monitoring of ionosphere VTEC using Multi‐GNSS carrier‐phase observations and B‐splines. Space Weather, 10.1029/2021sw002858, 2021

(Open Access)

Smirnov A.,Shprits Y., Zhelavskaya I., Lühr H., Xiong C., Goss A., Prol F., Schmidt M., Hoque M., Pedatella N., Szabó‐Roberts M.: Intercalibration of the Plasma Density Measurements in Earth's Topside Ionosphere. Journal of Geophysical Research: Space Physics, 10.1029/2021ja029334, 2021

Qi L., Hernández-Pajares M., Lyu H., Goss A.: Influence of temporal resolution on the performance of global ionospheric maps. Journal of Geodesy, 95(3), 10.1007/s00190-021-01483-y, 2021

Erdogan E., Schmidt M., Goss A., Görres B., Seitz F.: Adaptive Modeling of the Global Ionosphere Vertical Total Electron Content. Remote Sensing, 12(11), 1822, 10.3390/rs12111822, 2020

(Open Access)

Erdogan E., Schmidt M., Seitz F., Durmaz M.: Near real-time estimation of ionosphere vertical total electron content from GNSS satellites using B-splines in a Kalman filter. Annales Geophysicae, 35(2), 263-277, 10.5194/angeo-35-263-2017, 2017 (Open Access)

Gerzen T., Minkwitz D., Schmidt M., Erdogan E.: Analysis of different propagation models for the estimation of the topside ionosphere and plasmasphere with an ensemble Kalman filter. Annales Geophysicae, 38(6), 1171-1189, 10.5194/angeo-38-1171-2020, 2020

(Open Access)

Goss A., Hernández-Pajares M., Schmidt M., Roma-Dollase D., Erdogan E., Seitz F.: High-Resolution Ionosphere Corrections for Single-Frequency Positioning. Remote Sensing, 13, 12, 10.3390/rs13010012, 2020

(Open Access)

Goss A., Schmidt M., Erdogan E., Seitz F.: Global and Regional High-Resolution VTEC Modelling Using a Two-Step B-Spline Approach . Remote Sensing, 12(7), 1198, 10.3390/rs12071198, 2020

(Open Access)

Deutsches Geodätisches Forschungsinstitut

Prof. Dr.-Ing. habil. Florian Seitz

Technische Universität München
Arcisstraße 21
80333 München