IEEE 211-1977 pdf free.IEEE Standard Definitions of Terms for Radio Wave Propagation.
absorption.The irreversible conversion of theenergy of an electromagnetic wave into anotherform of energy as a result of its interactionwith matter.
acoustic gravity wave. In the atmosphere，alowfrequency wave whose restoring forces areboth compressional and gravitational.
albedo.The ratio of the reflected power to theincident power of radiation falling upon abody.
Alfven wave. In a magneto-ionic medium, themagnetohydrodynamic wave that propagates inthe direction of the static magnetic field,withassociated electric and magnetic fields and fluidparticle velocities oriented perpendicular to thedirection of propagation and with no associated density fluctuations in the medium.amplitude.Of a sinusoidal wave,the maximumvalue of a field quantity in space or time.angular frequency. of a periodic function，2times the frequency.antenna temperature.The temperature of ablackbodywhich，when placed around amatched antenna that is similar to the actualantenna but lossfree, produces . from . thisantenna the same available power，in a specified frequency range，as the actual antenna inits normal electromagnetic environment.
atmospheric duct. A layer in the tropospherewithin which radio waves of sufficiently highfrequency propagate with low rate of decreaseof amplitude with distance. The duct extendsfrom the level of a local minimum of themodified index of refraction as a function ofheight down to the level where the minimum value is again encountered,or down to thesurface bounding the atmosphere if the mini-mum value is not again encountered.
atmospherics. Transient burstsofelectro-magneticradiation arisingfrom naturalelectrical disturbances in the lower atmosphere.(The term “static” to include atmospherics andother radio noise was in early usage.)
attenuation. Of a quantity associated with atraveling wave in a slowly varying medium inwhich the refractive index changes are smallover distances comparable to a vacuum wave-length,the decrease of its amplitude withincreasing distance from the source,excludingthe decrease due to spreading.
attenuation constant.The real part of thepropagation constant.
attenuation ratio.The magnitude of thepropagation ratio.attenuation vector. Of a field quantity，thevector pointing in the direction of maximumdecrease of amplitude. The magnitude of thisvector is the attenuation constant.
aurora.Opticaland electrical phenomenaresulting from direct excitation or ionization ofupper atmospheric constituents by energeticparticles, generally at high latitudes.IEEE 211 pdf download.