Total electron content

The total electron content (TEC ) to German about the total electron content is a characteristic of the Earth's ionosphere. The TEC is the product of electron density and path and is measured in electrons per square meter. The electron surface density of 1016 electrons / m is the so-called TEC Unit ( TECU, often only TEC ).

Clearly corresponds to 1 TECU an open column with a base area of ​​1 by 1 meter, in which there are a total of 1016 electrons. For a uniform distribution of the electrons in this column and the assumption of a column height of 1000 km ( upper limit of the ionosphere ), the average electron density is 10,000 electrons per cubic centimeter.

The electron density ne in the ionosphere is not constant ( see picture). At the maximum, the F- layer, it is approximately 1 million ( free ) electrons per cm ³.

The TEC is path dependent. The calculation by integration along the path ds through the ionosphere with the position-dependent electron density ne ( s ):

A distinction is a vertical (VTEC ) and inclined TEC (STEC, slant for engl., Oblique). The VTEC is determined by integration of the electron density on a perpendicular to the ground standing route, the STEC is obtained by integrating over an arbitrary straight-line path.

The ionospheric TEC can be determined for example by the bottom-side observation of the signal change of satellite radio signals. Often this the signals from the GPS satellites can be used.

The TEC is strongly influenced by solar activity. In quiet times the daily value of 5 to 25 fluctuates When solar storms can reach values ​​greater than 200.