Total electron content
Encyclopedia
Total electron content is an important descriptive quantity for the ionosphere
of the Earth. TEC is the total number of electron
s present along a path between two points, with units of electrons per square meter, where 1016 electrons/m² = 1 TEC unit (TECU).
TEC is significant in determining the scintillation
and group delay
of a radio wave
through a medium. Ionospheric TEC is characterized by observing carrier phase delays of received radio signals transmitted from satellites located above the ionosphere, often using Global Positioning System
satellites. TEC is strongly affected by solar activity.
To first order, the observed phase of a radio source is retarded by an amount proportional to TEC and inversely proportional to the radio frequency. This can be written
where k is a proportionality constant equal to 1.3445x109 cyc·Hz/TECU = 1016·c·re/(2π), where c is the speed of light and re is the electron radius. Dividing the above equation by the radio frequency gives the ionospheric phase delay
while taking the derivative with respect to frequency gives the ionospheric group delay
Note the ionospheric phase and group delays have the same magnitude, but opposite sign.
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
of the Earth. TEC is the total number of electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s present along a path between two points, with units of electrons per square meter, where 1016 electrons/m² = 1 TEC unit (TECU).
TEC is significant in determining the scintillation
Scintillation
Scintillation can refer to:*Scintillation , atmospheric effects which influence astronomical observations*Interplanetary scintillation, fluctuations of radio waves caused by the solar wind...
and group delay
Group delay
Group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component...
of a radio wave
Radio Wave
Radio Wave may refer to:*Radio frequency*Radio Wave 96.5, a radio station in Blackpool, UK...
through a medium. Ionospheric TEC is characterized by observing carrier phase delays of received radio signals transmitted from satellites located above the ionosphere, often using Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
satellites. TEC is strongly affected by solar activity.
To first order, the observed phase of a radio source is retarded by an amount proportional to TEC and inversely proportional to the radio frequency. This can be written
where k is a proportionality constant equal to 1.3445x109 cyc·Hz/TECU = 1016·c·re/(2π), where c is the speed of light and re is the electron radius. Dividing the above equation by the radio frequency gives the ionospheric phase delay
while taking the derivative with respect to frequency gives the ionospheric group delay
Group delay
Group delay is a measure of the time delay of the amplitude envelopes of the various sinusoidal components of a signal through a device under test, and is a function of frequency for each component...
Note the ionospheric phase and group delays have the same magnitude, but opposite sign.