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The ionosphere is a layer of partially ionized gases high above the majority of the Earth's atmosphere; these gases are ionized by cosmic rays originating on the sun. When radio waves travel into this zone, which commences about 80 kilometers above the earth, they experience diffraction in a manner similar to the visible light phenomenon described above. [1]
Radio propagation is the behavior of radio waves as they travel, or are propagated, from one point to another in vacuum, or into various parts of the atmosphere. [1]: 26‑1 As a form of electromagnetic radiation, like light waves, radio waves are affected by the phenomena of reflection, refraction, diffraction, absorption, polarization, and scattering. [2]
Derivation of the optical invariant, a measure of the light propagating through an optical system.. The document ITU-R pp. 676–78 of the ITU-R section considers the atmosphere as being divided into spherical homogeneous layers; each layer has a constant refraction index.
Radio waves were first predicted by the theory of electromagnetism that was proposed in 1867 by Scottish mathematical physicist James Clerk Maxwell. [6] His mathematical theory, now called Maxwell's equations, predicted that a coupled electric and magnetic field could travel through space as an "electromagnetic wave".
Diffraction is the same physical effect as interference, but interference is typically applied to superposition of a few waves and the term diffraction is used when many waves are superposed. [1]: 433 Italian scientist Francesco Maria Grimaldi coined the word diffraction and was the first to record accurate observations of the phenomenon in 1660.
Refraction of radio waves by the ionosphere rather than the atmosphere can therefore allow NLOS links of much greater distance for just one refraction path or 'hop' via one of the layers. Under certain conditions radio waves that have undergone one hop may reflect off the Earth's surface and experience more hops, so increasing the range.
study of radio waves (the original area of research) study of radiation used in radiology [2] study of other ranges of the spectrum of electromagnetic radiation in some specific applications; Among the main applications of radiophysics are radio communications, radiolocation, radio astronomy and radiology.
In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and reflection from water bodies and terrestrial objects such as mountains and buildings.