Total electron content
The total electron content (TEC), to German about total electron content , is a characteristic of the ionosphere of the earth.
calculation
The TEC is calculated as:
- TEC =
With
- the way s through the ionosphere
- the path-dependent electron density n e (s) in the ionosphere (see second picture). In the maximum, the F-layer , the electron density is around 1 million (free) electrons per cm³.
One distinguishes
- a vertical TEC (vTEC), determined by integration over a section perpendicular to the ground
- an inclined TEC (sTEC, for slant , inclined), determined by integration over any straight path.
unit
The TEC is measured in electrons per square meter or in TEC units (TECU, often just TEC); a TECU corresponds to an electron areal density of 10 16 electrons / m.
Clearly, 1 TECU corresponds to an open column with a base area of 1 meter by 1 meter in which there are 10 16 electrons. With an even distribution of electrons in this column and assuming a column height of 1000 km (upper limit of the ionosphere), the average electron density is 10,000 electrons per cm³.
detection
The ionospheric TEC, for example, by the bottom-side observation of the signal change from satellites - Radio signals are determined. The signals from the GPS satellites are often used for this purpose .
The TEC is strongly influenced by solar activity : in quiet times the daily value fluctuates between 5 and 25 TECU, during solar storms it can also reach values greater than 200 TECU.
Web links
The following web links are in English.
- Current 2D map of the TEC: NASA: Ionospheric and Atmospheric Remote Sensing
- Current 3D view of the TEC via Google Earth: NASA: 4D Ionosphere
Individual evidence
- ↑ Heise, Stefan: The ionosphere and plasmasphere of the earth dissertations online
- ↑ C. Stolle *, S. Schlüter °, N. Jakowski °, Ch. Jacobi *, S. Heise °, A. Raabe *: Tomography in the ionosphere with integration of GPS occultations (PDF; 380 kB)