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Ionospheric absorption (or ISAB) is the scientific name for absorption occurring as a result of the interaction between various types of
ISAB is only a factor in the period of the day where radio signals travel through the portion of the ionosphere facing the sun. The
Ionospheric absorption (or ISAB) is the scientific name for absorption occurring as a result of the interaction between various types of electromagnetic waves
In physics, electromagnetic radiation (EMR) consists of waves of the electromagnetic (EM) field, which propagate through space and carry momentum and electromagnetic radiant energy. It includes radio waves, microwaves, infrared, (visible) lig ...
and the free electrons in the ionosphere, which can interfere with radio
Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transm ...
transmissions.
Description
Ionosphere absorption is of critical importance whenradio network
There are two types of radio network currently in use around the world: the one-to-many ( simplex communication) broadcast network commonly used for public information and mass-media entertainment, and the two-way radio ( duplex communication) typ ...
s, telecommunication systems or interlinked radio systems are being planned, particularly when trying to determine propagation conditions.Walker, J.K. ; Bhatnagar, V.P. Ionospheric absorption, typical ionization, conductivity, and possible synoptic heating parameters in the upper atmosphere Upper atmosphere is a collective term that refers to various layers of the atmosphere of the Earth above the troposphere and corresponding regions of the atmospheres of other planets, and includes:
* The mesosphere, which on Earth lies between the ...
. Geological Survey of Canada.http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=6068491
The ionosphere can be described as an area of the atmosphere in which radio waves
Radio waves are a type of electromagnetic radiation with the longest wavelengths in the electromagnetic spectrum, typically with frequencies of 300 gigahertz ( GHz) and below. At 300 GHz, the corresponding wavelength is 1 mm (s ...
on shortwave bands
Shortwave bands are frequency allocations for use within the shortwave radio spectrum (the upper medium frequency Fband and all of the high frequency Fband). Radio waves in these frequency ranges can be used for very long distance (transcontinent ...
are refracted or reflected back to earth. As a result of this reflection, which is often key in the long-distance propagation of radio waves, some of the shortwave signal strength is decreased. In this regard, ISAB is the primary limiting factor
A limiting factor is a variable of a system that causes a noticeable change in output or another measure of a type of system. The limiting factor is in a pyramid shape of organisms going up from the producers to consumers and so on. A factor not l ...
in radio propagation.
Attenuation mechanics
ISAB is only a factor in the period of the day where radio signals travel through the portion of the ionosphere facing the sun. The solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the ...
and radiation cause the ionosphere to become charged with electrons in the first place. At night, the atmosphere becomes drained of its charge, and radio signals can go much farther with less loss of signal. In particular, low frequency signals that would be attenuated to nothing during the day will be received much farther away at night.John Keith Hargreaves. The Solar-Terrestrial Environment: An Introduction to Geospace. 1992 Cambridge University Press. Leo F. McNamara. (1994) Radio Amateurs Guide to the Ionosphere.
The specific amount of attenuation can be derived as a function of the Inverse-square law
In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. The fundamental cause for this can be unde ...
. The lower the frequency, the greater the attenuation.
Relative ionospheric absorption can be measured using a riometer
A riometer (commonly ''r''elative ''i''onospheric ''o''pacity meter, although originally: Relative Ionospheric Opacity Meter for Extra-Terrestrial Emissions of Radio noise) is an instrument used to quantify the amount of electromagnetic-wave ion ...
.
See also
* Radio horizon *Sudden Ionospheric Disturbance A sudden ionospheric disturbance (SID) is any one of several ionospheric perturbations, resulting from abnormally high ionization/plasma density in the D region of the ionosphere and caused by a solar flare and/or solar particle event (SPE). The S ...
Resources
Ionosphere Radio frequency propagation {{astrophysics-stub