1、44 CCIR RECflN*310-8 92 Y855212 052031Y 281 = Rec. 310-8 RECOMMENDATION 3 10-8 DEFINITIONS OF TERMS RELATING TO PROPAGATION IN NON-IONIZED MEDIA (195 1- 1959-1966-1970- 1974- 1978-1982- 1986-1990- 1992) The CCIR, considering that it is important to have agreed definitions of propagation terns used i
2、n the texts of Study Group 5, recommends that the list of definitions annexed hereto be adopted for incorporation in the vocabulary; VOCABULARY OF TERMS USED IN RADIO PROPAGATION IN NON-IONIZED MEDIA Term Definition A. Terns related to radio waves Al. Cross-polarization The appearance, in the course
3、 of propagation, of a polarization component which is orthogonal to the expected polarization. A2. Cross-polarization For a radio wave transmitted with a given polarization, the ratio at the reception point of the power received with the expected polarization to the power received with the orthogona
4、l polarization. Note I - The cross-polarization discrimination depends both on the characteristics of the antenna and on the propagation medic. For two radio waves transmitted with the same frequency with the same power and orthogonal polarization, the ratio of the co-polarized power in a given rece
5、iver to the cross-polarized power in that receiver. discrimination A3. Cross-polarization isolation A4. Depolarization A phenomenon by virtue of which all or part of the power of a radio wave transmitted with a defined polarization may no longer have a defined polarization after propagation. B. Term
6、s related to ground effects on radio-wave propagation B 1, Free-space propagation B2. Line of sight propagation Propagation of an electromagnetic wave in a homogeneous ideal dielectric medium which may be considered of infinite extent in all directions. Propagation between two points for which the d
7、irect ray is sufficiently clear of obstacles for diffraction to be of negligible effect. B3. Radio horizon The locus of points at which direct rays from a point of radio waves are tangential to the surface of the Earth. Note I - As a general rule, the radio and geometric horizons are different becau
8、se of atmospheric refraction. B4. Penetration depth The depth within the Earth at which the amplitude of a radio wave incident at the surface falls to a value lle (0.368) of its value at the surface. CCIR Rec. 310-8 45 A surface separating two media which is sufficiently large and the irregularities
9、 of which are sufficiently small to cause specular reflection. B5. Smooth surface; specular sitrface Note 1 - In practice, the minimum size of the surface corresponds to the first Fresnel zone and the importance of irregularities is estimated using the Rayleigh criterion. A surface separating two me
10、dia which does not fulfil the smooth surface conditions and the irregularities of which are randomly located and cause diffuse reflection. B6. Rough siirJ5ace B7. Diffiise reflection coeflcient The ratio of the amplitude of the incoherent wave reflected from a rough surface to the amplitude of the i
11、ncident wave. B8. Measitre of terrain irregularity; Ah A statistical parameter which characterizes the variations in ground height along part or all of a propagation path. Note 1 - For example, Ah is often defined as the difference between the heights exceeded by 10% and 90% respectively of the terr
12、ain heights measured at regular intervals (the interdecile height range) along a specified section of a path. B9. Obstacle gain The ratio of the electromagnetic field due to edge diffraction by an isolated obstacle to the field which would occur due only to spherical diffraction in the absence of th
13、e obstacle. C. Terms related to tropospheric effects on radio-wave propagation C1. Troposphere The lower part of the Earths atmosphere extending upwards from the Earths surface, in which temperature decreases with height except in local layers of temperature inversion. This part of the atmosphere ex
14、tends to an altitude of about 9 km at the Earths poles and 17 km at the equator. C2. Temperatrtre inversion (in the troposphere) An increase in temperature with height in the troposphere. C3. Mixing ratio The ratio of the mass of water vapour to the mass of dry air in a given volume of air (generall
15、y expressed in gkg). C4. Refractive index; n Ratio of the speed of radio waves in vacuo to the speed in the medium under consideration. C5. Refractivity; N One million times the amount by which the refractive index iz in the atmosphere exceeds unity: N = (n - 1) lo6 C6. N-ititit A dimensionless unit
16、 in terms of which refractivity is expressed. C7. Modified refractive index The sum of the refractive index ri of the air at height h and the ratio of this height to the radius of the Earth, a: h a Il + - C8. Refractive modidits; M One million times the amount by which the modified refractive index
17、exceeds unity: c9. M-mit A dimensionless unit in terms of which refractive modulus M is expressed. CCIR RECMN*310-8 92 m 4855212 0520423 175 m 46 C10. Standard refractivity gradient C 1 1. Standard radio atmosphere C12. Reference atmosphere for refraction C13. Sub-reffaction C14. Super refraction C1
18、5. Effective radius of the Earth C 16, Effective Eurth-radius factor: k CI 7. Ducting luyer C18. Tropospheric radio-duct C19. Ground-based duct (Su rfu ce du ct) C20. Elevated duct C21. Duct thickness C22. Duct height Rec. 310-8 A standard value of vertical gradient of refractivity used in refractio
19、n studies; namely -40 N/km. This corresponds approximately to the median value of the gradient in the first kilometre of altitude in temperate regions. An atmosphere having the standard refractivity gradient. An atmosphere in which n(h) decreases with height as given by equation (2) of Recommendatio
20、n 369. Refraction for which the refractivity gradient is greater (i.e. positive or less negative) than the standard refractivity gradient. Refraction for which the refractivity gradient is less (Le. more negative) than the standard refractivity gradient. Radius of a hypothetical spherical Earth, wit
21、hout atmosphere, for which propagation paths are along straight lines, the heights and ground distances being the same as for the actual Earth in an atmosphere with a constant vertical gradient of refractivity. Note 1 - The concept of effective radius of the Earth implies that the angles with the ho
22、rizontal planes made at all points by the transmission paths are not too large. Note 2 - For an atmosphere having a standard refractivity gradient, the effective radius of the Earth is about 4/3 that of the actual radius, which corresponds to approximately 8 500 km. Ratio of the effective radius of
23、the Earth to the actual Earth radius. Note I - This factor k is related to the vertical gradient dnldh of the refractive index n and to the actual Earth radius a by the equation: 1 dn k= 1+az A tropospheric layer characterized by a negative M gradient, which consequently may generate a tropospheric
24、radio-duct if the layer is sufficiently thick compared with the wavelength. A quasi-horizontal stratification in the troposphere within which radio energy of a sufficiently high frequency is substantially confined and propagates with much lower attenuation than would be obtained in a homogeneous atm
25、osphere. Note 1 - The tropospheric radio-duct consists of a ducting layer and, in the case of an elevated duct, the portion of the underlying atmosphere in which the refractive modulus exceeds the minimum value attained in the ducting layer. A tropospheric radio-duct in which the lower bounary is th
26、e surface of the Earth. A tropospheric radio-duct in which the lower boundary is above the surface of the Earth. The difference in Leight between the upper and lower boundaries of a tropospheric radio-duct. The height above the surface of the Earth of the lower boundq of an elevated duct. *CCIR RECM
27、N*3LO-B 92 4855212 0520424 O01 = C23. Duct intensity C24. Ducting C25. Trans-horizon propagation C26. Tropospheric-scatter propagation C27. Hydrometeors C28. Aerosols C29. Precipitation-scatter C30. Midtipath propagation C31. Scintillation propagation C32. Gain degradation; antenna to rnediutn collp
28、liilg loss C3 3. Precipitation rate; rairll rate; rain rate Rec. 310-8 47 The difference between the maximum and minimum values of the refractive modulus in a tropospheric radio-duct. Note 1 - The intensity of a duct is the same as that of its ducting layer. Guided propagation of radio waves inside
29、a tropospheric radio-duct. Note 1 - At sufficiently high frequencies, a number of electromagnetic modes of guided propagation can coexist in the same tropospheric radio-duct. Tropospheric propagation between points close to the ground, the reception point being beyond the radio horizon of the transm
30、ission point. Note 1 - Trans-horizon propagation may be due to a variety of tropospheric mechanisms such as diffraction, scattering, reflection from tropospheric layers. However ducting is not included because in a duct there is no radio horizon. Tropospheric propagation due to scattering from many
31、inhomogeneities and discontinuities in the refractive index of the atmosphere. Concentrations of water or ice particles which may exist in the atmosphere or be deposited on the surface of the Earth. Note 1 -Rain, fog, clouds, snow and hail are the main hydrometeors. Small particles in the atmosphere
32、 (other than fog or cloud droplets) which do not fall rapidly under gravity. Tropospheric propagation due to scattering caused by hydrometeors, mainly rain. Propagation of the same radio signai between a transmission point aid a reception point over a number of separate propagation paths. Rapid and
33、random fluctuation in one or more of the characteristics (amplitude, phase, polarization, direction of arrival) of a received signal, caused by refractive index fluctuations of the transmission medium. The apparent decrease in the sum of the gains (expressed in decibels) of the transmitting and receiving antennas when significant scattering effects occur on the propagation path. A measure of the intensity of precipitation expressed by the increase in the height of water reaching the ground per unit time. Note 1 - Rain rate is generally expressed in millimetres per hour,
