1、 Recommendation ITU-R P.527-4 (06/2017) Electrical characteristics of the surface of the Earth P Series Radiowave propagation ii Rec. ITU-R P.527-4 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by
2、 all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Confer
3、ences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements an
4、d licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available
5、 online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite serv
6、ices P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and fr
7、equency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2017 ITU 2017 All rights reserved. No part of this publication may be reproduced, by any means what
8、soever, without written permission of ITU. Rec. ITU-R P.527-4 1 RECOMMENDATION ITU-R P.527-4 Electrical characteristics of the surface of the Earth (1978-1982-1992-2017) Scope This Recommendation gives methods to model the electrical characteristics of the surface of the Earth, including pure water,
9、 sea water, ice, soil and vegetation cover, for frequencies up to 1 000 GHz, in a systematic manner based on the evaluation of complex relative permittivity. In all cases conductivity can be calculated as a function of frequency and temperature from these evaluations. Previous information on electri
10、cal characteristics below 30 MHz in terms of permittivity and conductivity is retained in Appendix in view of its association with Recommendations ITU-R P.368 and ITU-R P.832. The new modelling method is fully compatible with this earlier information. Keywords Complex permittivity, conductivity, pen
11、etration depth, Earths surface, water, vegetation, soil, ice The ITU Radiocommunication Assembly, considering a) that the electrical characteristics may be expressed by three parameters: magnetic permeability, electrical permittivity, , and electrical conductivity, ; b) that the permeability of the
12、Earths surface, , can normally be regarded as equal to the permeability in a vacuum; c) that the electrical properties of the Earths surface can be expressed by the complex permittivity or, equivalently, by the real part and imaginary part of the complex permittivity; d) that information on the vari
13、ation of the penetration depth with frequency is needed; e) that knowledge of the electrical characteristics of the Earths surface is needed for several purposes in propagation modelling, including ground-wave signal strength, ground reflection at a terrestrial terminal, interference between aeronau
14、tical and/or space borne stations due to reflections or scattering from the Earths surface, and for Earth science applications; f) that Recommendation ITU-R P.368 contains ground-wave propagation curves from 1 MHz to 30 MHz for different ground conditions characterised by permittivity and electrical
15、 conductivity; g) that Recommendation ITU-R P.832 contains a world atlas of ground electrical conductivity for frequencies below 1 MHz, recommends that the information in Annex 1 be used to model the electrical characteristics of the surface of the Earth. 2 Rec. ITU-R P.527-4 Annex 1 1 Introduction
16、This Annex provides prediction methods that predict the electrical characteristics of the following Earths surfaces for frequencies up to 1 000 GHz: Water Sea (i.e. Saline) Water Dry and Wet Ice Dry and Wet Soil (combination of sand, clay, and silt) Vegetation (above and below freezing) 2 Complex pe
17、rmittivity The characteristics of the Earths surface can be characterized by three parameters: the magnetic permeability, , the electrical permittivity, , and the electrical conductivity1, . Magnetic permeability is a measure of a materials ability to support the formation of a magnetic field within
18、 itself in response to an applied magnetic field; i.e. the magnetic flux density B divided by the magnetic field strength H. Electrical permittivity is a measure of a materials ability to oppose an electric field; i.e. the electrical flux density D divided by the electrical field strength E. Electri
19、cal conductivity is a measure of a materials ability to conduct an electric current; i.e. the ratio of the current density in the material to the electric field that causes the current flow. Given an incident plane wave (,) = 0(), with radial frequency , time , magnetic permeability , electrical per
20、mittivity , and electrical conductivity , the propagation wave number vector , has a magnitude given by = (+) (1a) The vacuum values of permittivity, permeability, and conductivity are: Vacuum Permittivity 0 = 8.854 187 817 1012 (F/m) Vacuum Permeability 0 = 4 107 (N/A2) Vacuum Conductivity 0 = 0.0
21、(S/m) It is convenient to define the relative permittivity, , and the relative permeability, , relative to their vacuum values as follows: Relative Permittivity = 0 Relative Permeability = 0where and are the associated permittivity and permeability of the medium. This Recommendation assumes = 0, in
22、which case = 1. 1 It is called electrical conductivity to differentiate it from other conductivities such as thermal conductivity and hydraulic conductivity. It is called hereinafter as conductivity. Rec. ITU-R P.527-4 3 As shown in equation (1a) the wavenumber depends on both and , not either separ
23、ately. Also formulations of other physical parameters describing various radio wave propagation mechanisms such as scattering cross section, reflection coefficients, and refraction angles, depend on values of this combination. Furthermore, the square root of this combination is equivalent to the ref
24、ractive index formulation used in characterizing the troposphere and the ionosphere. The refractive index is also used in characterizing different materials at the millimetre wave and optical frequency bands. Accordingly, to simplify the formulations describing various propagation mechanisms and to
25、standardize terminologies of electrical characteristics at different frequency bands, the combination is defined as the complex permittivity and used to describe the electrical characteristics of substances. While permittivity refers to , relative permittivity refers to , and complex relative permit
26、tivity, defined as , refers to: = 0 0(1b) where may be complex. In equation (1b), is the real part of the complex permittivity, and is the imaginary part of the complex permittivity. The real part of the complex relative permittivity, , is associated with the stored energy when the substance is expo
27、sed to an electromagnetic field. The imaginary part of the complex relative permittivity, , influences energy absorption and is known as the loss factor. The minus sign in equation (1b) is associated with an electromagnetic field having time dependence of 2 ( is frequency in Hz, and is time in secon
28、ds). If the time dependence is 2, the minus () sign in equation (1b) is replaced by a plus (+) sign. At frequencies up to 1 000 GHz, dissipation within the Earths surface is attributed to either translational (conduction current) charge motion or vibrational (dipole vibration) charge motion, and the
29、 imaginary part of the complex relative permittivity, can be decomposed into two terms: = + 20(2) where represents the dissipation due to displacement current associated with dipole vibration, and 20 represents the dissipation due to conduction current. Conduction current consists of the bulk transl
30、ation movement of free charges and is the only current at zero (i.e. dc) frequency. Conduction current is greater than displacement current at frequencies below the transition frequency, , and the displacement current is greater than the conduction current at frequencies above the transition frequen
31、cy, . The transition frequency, , defined as the frequency where the conduction and displacement currents are equal, is: t = 20d(3) For non-conducting (lossless) dielectric substances = 0, and hence = . For some of those substances, such as dry soil and dry vegetation, = 0, and hence = 0 irrespectiv
32、e of the frequency, which is the case considered in 2.1.2.3 of Recommendation ITU-R P.2040. On the other hand, for some other non-conducting substances, such as pure water and dry snow, , and hence , equal zero only at zero frequency. Accordingly, 2.1.2.3 of Recommendation ITU-R P.2040 cannot be app
33、lied to those substances. For conducting (lossy) dielectric substances, such as sea water and wet soil, the electrical conductivity has finite values different than zero. Accordingly, as the frequency tends to zero, the imaginary part of the complex relative permittivity of those substances tends to
34、 as it can be inferred from equation (3). In this case, it is easier to work with the conductivity instead of the imaginary part of 4 Rec. ITU-R P.527-4 the complex relative permittivity which can be written from equation (2) after setting = 0 as follows: = 20f = 0.05563GHz (3a) with GHz is the freq
35、uency in GHz. Generalizing the above formulation to other frequencies, as done by equation (12) of Recommendation ITU-R P.2040, yields the sum of two terms: one term gives the electrical conductivity and the other term accounts for the power dissipation associated with the displacement current. This
36、 Recommendation provides prediction methods for the real and imaginary parts of the complex relative permittivity, and ; and the accompanying example figures show trends of the real and imaginary parts of the complex relative permittivity with frequency under different environmental conditions. 2.1
37、Layered ground The models in 5 apply to homogeneous sub-surface soil; however, the sub-surface is rarely homogeneous. Rather, it consists of multiple layers of different thicknesses and different electrical characteristics that must be taken into account by introducing the concept of effective param
38、eters to represent the homogeneous soil. Effective parameters can be used with the homogeneous smooth Earth ground-wave propagation curves of Recommendation ITU-R P.368. 3 Penetration depth The extent to which the lower strata influence the effective electrical characteristics of the Earths surface
39、depends upon the penetration depth of the radio energy, , which is defined as the depth at which the amplitude of the field strength of electromagnetic radiation inside a material falls to 1/e (about 37%) of its original value at (or more properly, just beneath) the surface. The penetration depth, ,
40、 in a homogeneous medium of complex relative permittivity ( = ) is given by: = 2 2( )2+ ()2 (m) (4) where is the wavelength in metres. Note that as the imaginary part of the complex relative permittivity in equation (4) tends to zero, the penetration depth tends to infinity. Figure 1 depicts typical
41、 values of penetration depth as a function of frequency for different types of Earths surface components including pure water, sea water, dry soil, wet soil, and dry ice. The penetration depths for pure water and sea water are calculated at 20 oC, and the salinity of sea water is 35 g/kg. The penetr
42、ation depths for dry soil and wet soil assume the volumetric water content is 0.07 and 0.5, respectively. Other soil parameters are the same as in Fig. 7. The penetration depth of dry ice is calculated at 0 oC. Rec. ITU-R P.527-4 5 FIGURE 1 Penetration depth of surface types as a function of frequen
43、cy P . 0 5 7 - 02 10 . 0 1 0 . 1 1 10 100 1 0000 . 0 0 10 0.0. 11101 001 00 0Penetrationdepth(m)Fre q u en cy GHz ( )Pu re w at erSea w at erD ry s o i lW et s o i lD ry i ce4 Factors determining the effective electrical characteristics of soil The effective values of the electrical characteristics
44、of the soil are determined by the nature of the soil, its moisture content, temperature, general geological structure, and the frequency of the incident electromagnetic radiation. 4.1 Nature of the soil Although it has been established by numerous measurements that values of the electrical character
45、istics of soil vary with the nature of the soil, this variation may be due to its ability to absorb and retain moisture rather than the chemical composition of the soil. It has been shown that loam, which normally has a conductivity on the order of 102 S/m can, when dried, have a conductivity as low
46、 as 104 S/m, which is the same order as granite. 4.2 Moisture content The moisture content of the ground is the major factor determining the permittivity and conductivity of the soil. Laboratory measurements have shown that as the moisture content of the ground increases from a low value, the permit
47、tivity and conductivity of the ground increase and reach their maximum values as the moisture content approaches the values normally found in such soils. At depths of one metre or more, the wetness of the soil at a particular site is typically constant. Although the wetness may increase during perio
48、ds of rain, the wetness returns to its typical value after the rain has stopped due to drainage and surface evaporation. The typical moisture content of a particular soil may vary considerably from one site to another due to differences in the general geological structure which provides different drainage. 6 Rec. ITU-R P.527-4 4.3 Temperature Laboratory measurements of the electrical characteristics of soil have shown that, at low frequencies conductivity increases by
