In telecommunications, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals (and light rays) are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if the ducts were not present. The duct acts as an atmospheric dielectric waveguide and limits the spread of the wavefront to only the horizontal dimension.
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| - Atmospheric duct (en)
- Conductos troposféricos (es)
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| - In telecommunications, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals (and light rays) are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if the ducts were not present. The duct acts as an atmospheric dielectric waveguide and limits the spread of the wavefront to only the horizontal dimension. (en)
- Un conducto troposférico es un espacio en el cual una onda electromagnética con rangos de frecuencia que oscilan en las bandas de VHF(Very High Frequency) y UHF(Ultra High Frequency) queda confinada entre dos masas de aire, creando un efecto similar a las guías de onda. Estas masas de aire están superpuestas, esto debido a un cambio en la temperatura que ocurre en la noche por la ausencia de calor y de corrientes de convección, a esto se le conoce como inversión de temperatura, haciendo que el aire caliente pierda densidad y ascienda sobre el aire más frío cercano a la superficie terrestre, creando un conducto que da lugar a un fenómeno de súper refracción, este conducto se conoce como conducto de superficie, debido a que está próximo a la superficie de la tierra. En las primeras horas de (es)
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| - In telecommunications, an atmospheric duct is a horizontal layer in the lower atmosphere in which the vertical refractive index gradients are such that radio signals (and light rays) are guided or ducted, tend to follow the curvature of the Earth, and experience less attenuation in the ducts than they would if the ducts were not present. The duct acts as an atmospheric dielectric waveguide and limits the spread of the wavefront to only the horizontal dimension. Atmospheric ducting is a mode of propagation of electromagnetic radiation, usually in the lower layers of Earth’s atmosphere, where the waves are bent by atmospheric refraction. In over-the-horizon radar, ducting causes part of the radiated and target-reflection energy of a radar system to be guided over distances far greater than the normal radar range. It also causes long distance propagation of radio signals in bands that would normally be limited to line of sight. Normally radio "ground waves" propagate along the surface as creeping waves. That is, they are only diffracted around the curvature of the earth. This is one reason that early long distance radio communication used long wavelengths. The best known exception is that HF (3–30 MHz.) waves are reflected by the ionosphere. The reduced refractive index due to lower densities at the higher altitudes in the Earth's atmosphere bends the signals back toward the Earth. Signals in a higher refractive index layer, i.e., duct, tend to remain in that layer because of the reflection and refraction encountered at the boundary with a lower refractive index material. In some weather conditions, such as inversion layers, density changes so rapidly that waves are guided around the curvature of the earth at constant altitude. Phenomena of atmospheric optics related to atmospheric ducting include the green flash, Fata Morgana, superior mirage, mock mirage of astronomical objects and the Novaya Zemlya effect. (en)
- Un conducto troposférico es un espacio en el cual una onda electromagnética con rangos de frecuencia que oscilan en las bandas de VHF(Very High Frequency) y UHF(Ultra High Frequency) queda confinada entre dos masas de aire, creando un efecto similar a las guías de onda. Estas masas de aire están superpuestas, esto debido a un cambio en la temperatura que ocurre en la noche por la ausencia de calor y de corrientes de convección, a esto se le conoce como inversión de temperatura, haciendo que el aire caliente pierda densidad y ascienda sobre el aire más frío cercano a la superficie terrestre, creando un conducto que da lugar a un fenómeno de súper refracción, este conducto se conoce como conducto de superficie, debido a que está próximo a la superficie de la tierra. En las primeras horas de la mañana, cuando la temperatura de la tierra aumenta empiezan a aparecer las corrientes de convección haciendo que el conducto generado anteriormente se convierta en un conducto elevado, esto, debido a que las dos masas de aire se vuelven una atmósfera homogénea por el efecto de las corrientes de convección. (es)
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