1、- 4855Z12 0541640 BOT INTERNATIONAL TELECOMMUNICATION UNION HANDBOOK ON RADIOMETEOROLOGY RADIOCOMMUNICATION EUREAU Geneva, 1996 4855232 0543b4L 74b INTERNATIONAL TELECOMMUNICATION UNION HANDBOOK ON RADIOMETEOROLOGY RAD I OCO M M U N I CAT I 0 N Geneva, 1996 6 U R EAU 4855232 0543b42 682 U HANDBOOK O
2、N RADIOMETEOROLOGY N:WRSGBSG3WANDBK 1. W W6 W 4855212 0541ih43 519 W . - 111 - PREFACE This Handbook on Radiometeorology has been developed by experts of Working Party 35 (Propagation fundamentais) of ITU-R Study Group 3 (Radiowave Propagation), under the chairmanship of Professor Gert Bmssaard (Net
3、herlands). N:BRSGBSG3HANDBKI .WW6 Previous page is blank. 4855232 0543644 455 I . iv . CONTENTS Chapter 1 Introduction 1.1 1.2 1.3 Chapter 2 2.1 2.2 2.3 2.3.1 2.3.2 2.3.3 2.3.4 2.4 2.4.1 2.4.2 2.4.3 2.4.4 2.5 2.5.1 2.5.2 2.6 2.6.1 2.6.2 2.6.3 2.7 2.8 Annex 1 Purpose ofthe Handbook on Radiometeorolog
4、y . Applicable texts . Cross-reference table . Physical characteristics of the atmosphere Variability of water vapour density and oxygen density at ground level Precipitation characteristics . Drop size distnbutron . Hydrometeor shape and orientation . Terminal velocity . Variability of the height p
5、rofile of water vapour . . Drop temperature . Statistical characteristics of rainfall intensity at a point Cumulative distribution of rainfall intensity Conversion of rainfall rate distributions to equivalent one-minute statistics Models for the rainfall rate distribution . Statistics of rainfall ev
6、ent duration Horizontal structure of rainfall . Application to scattering by rain Application to attenuation by rain . Vertical structure of precipitation Vertical variation of reflectivity . Vertical variation of specific attenuation . The 0C isotherm height and the rain height . Characteristics of
7、 fog and clouds . Sand and dust-storms . Types of precipitation Page 1 1 1 2 3 3 3 3 3 4 4 4 5 5 6 7 8 8 8 9 10 11 11 12 14 14 15 N:BRSGBSG3HANDBKI . WW6 m 4855232 05Lilb45 331 1 -v- hex 2 Rain climatology models . A 2.1 Introduction A 2.2 The modified Moupfouma model A 2.3 The Boithias model A 2.4
8、The Flavin model . References Chapter 3 3.1 3.1.1 3.1.2 3.1.3 3.1.4 3.2 3.2.1 3.2.2 3.3 3.3.1 3.3.2 3.3.3 3.3.4 3.3.5 3.4 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 3.4.6 3.5 3.5.1 Atmospheric refraction Influence of the atmosphere on radiowave propagation Refractive index and refractivity . Models of the atmosp
9、heric refractive index . Departures from the models . Refractivity at ground level . Introduction Monthly averages of ground refractivity . Refractivity gradients . Generalities Models for refractivity gradient distribution Statistical information on refiactivity gradients Correlation between ground
10、 refractivity and refractivity gradient Equivalent refractivity gradient along a path . Refractive structures at mid and large scales . Ducting layers - definition and experimental observations . General . Duct modelling Duct statistics . Sub-refractive conditions . Statistics of sub-refractive cond
11、itions Horizontal refractivity gradients Techniques of refractive index measurements . General . Page 16 16 16 17 17 19 22 22 22 22 25 26 27 27 27 28 28 28 31 32 32 33 33 33 35 36 36 36 37 37 N.BRSGBSG3HANDBKI . WW6 4855232 05i.ILb4b 228 W . vi . 3.5.2 Direct measurements . microwave refractometers
12、. 3.5.3 Indirect measurements . 3.5.4 Humidity measurements 3.5.5 Measurement of vertical profiles . 3.5.6 Measurements of vertical and horizontal structures References Chapter 4 Influence of refraction on propagation . 4 4.1 4.1.1 4.1.2 4.1.3 4.2 4.2.1 4.2.2 4.2.3 4.2.4 4.2.5 4.3 4.3.1 4.3.2 4.4 4.
13、4.1 4.4.2 4.4.3 4.4.4 4.4.5 4.5 4.5.1 Influence of refraction on propagation . General . Introduction Ray approximation . Modified refiactive index and effective Earth radius Refractive effects in normal conditions . Sub-refiaction and super-refraction . Apparent elevation angle . Radioelectric path
14、 length . Beam spreading on slant paths . Range rate error Propagation during sub-refractive conditions Effective Earth radius factor for the path, k, Propagation with super-refractive layers . Qualitative descnption by ray tracing Ducting effects . Mui tipath propagation Angle-of-arrival variations
15、., . Representation of the propagation channel during super-refractive conditions Prediction of the minimum value of ke General . General . Page 37 39 40 43 43 44 67 67 67 67 67 68 69 69 70 71 73 74 75 75 76 77 77 77 79 82 84 84 84 N:BRSGBSG3HANDBKl . WW6 4855232 054lib47 lib4 . vii . 4.5.2 4.5.3 4.
16、5.4 4.5.5 4.6 4.6.1 4.6.2 4.7 4.7.1 4.7.2 4.7.3 Multi-ray model . Theoretical considerations on single-frequency statistics Models for the multipath transfer function Simplified representations of the propagation channel Signal scintillations due to atmospheric turbulence Amplitude scintillation Ang
17、le-of-arrivai scintillations Tropospheric scatter propagation . Modelling of long term variations of field strength . Troposcatter transfer function . General . References Chapter 5 Single-particle scattering . 5.1 General considerations . 5.1.1 5.1.2 5.2 Solution methods . 5.2.1 Analytical methods
18、Integral representation of the field . Scattering of a plane wave in the far field . The optical theorem . 5.2.2 Approximate numerical methods . 5.3 Numerical implementation Chapter 6 Attenuation and dispersion by atmospheric gases . Calculation of specific attenuation using simple algorithms . Disp
19、ersion due to atmospheric gases . References . 6.1 Introduction 6.2 6.3 6.4 6.5 Attenuation of infrared and visible radiation . References . Chapter 7 Attenuation by atmospheric particles . 7.1 7.1.1 Introduction Calculation of attenuation along Earth-space paths . Attenuation due to hydrometeors .
20、Page 84 85 85 87 88 88 91 93 93 94 95 98 102 102 103 104 108 108 113 118 120 122 122 124 128 129 135 139 140 140 140 N:BRSGBSG3VIANDBKl . WW6 4855232 0541b48 OTO . . v111 . 7.1.2 7.1.3 7.1.4 7.1.5 7.1.6 7.2 7.3 7.3.1 7.4 References Chapter 8 Radio emissivity of atmosphere and ground Prediction of sp
21、ecific attenuation from rainfall intensity data . Attenuation over propagation links of finite extent . Prediction of attenuation from radio propagation data Variability of rain attenuation statistics . Propagation delay due to precipitation Radiometer and radar measurements . Attenuation by hydrome
22、teors other than rain Aerosols, fog, clouds, hail and snow . Attenuation by sand and dust storms . 8.1 8.2 8.2.1 8.2.2 8.2.3 8.3 8.4 8.5 8.5.1 8.5.2 8.5.3 8.6 8.6.1 8.6.2 8.63 8.6.4 Introduction Radiative transfer . Fundamentals . Radiative transfer equation Brightness temperature Atmospheric emissi
23、vity . Ground emissivity Radiometric estimation of attenuation and path length . General . Radiometric estimation of attenuation . Estimation of propagation path delay Passive remote sensing of atmospheric composition . General . Atmospheric water content Radiometric retrieval of atmospheric water c
24、ontent Retrieval and scaling coefficients References Chapter 9 Cross-polarization and anisotropy . 9.1 Introduction 9.2 Mathematical background Page 140 143 146 148 148 150 150 150 154 155 162 162 163 163 164 166 166 169 170 170 171 172 173 173 173 174 175 177 185 185 185 N:BRSGBSG3VIANDBKI . WW6 .
25、ix- 9.2.1 Polarization state of a wave . 9.2.2 Duai-polarization transfer channel . 9.2.3 Simplified medium models Chapter 1 O Statistical aspects of modelling . 10.1 10.1.1 10.1.2 10.1.3 10.2 10.2.1 10.2.2 10.2.3 10.2.4 10.3 10.3.1 10.3.2 10.4 10.5 Variability of atmospheric processes . Introductio
26、n Definitions . Concepts and models . Worst month statistics The ITU-R definition . Calculation method using Q Calculation method using Co . Variability aspects Annuai statistics . Vanability aspects . Accuracy and model testing . Risk and retuni period Conclusions Annex 1 O.A. 1 Rank-order statisti
27、cs Annex 10.A.2 Determination of Co and Ci from measured data . Annex 10.A.3 Risk assessment . References Page 185 187 189 192 192 192 192 194 195 195 196 197 197 198 198 198 199 200 203 204 205 206 N.BRSGBSGSiANDBKI . WW6 - - 4855212 0541b50 753 -1- CHAPTER 1 Introduction 1.1 This Handbook provides
28、 general information on radiometeorology for those who use the ITU-R P series of Recommendations and those who wish to evaluate andor develop these Recommendations. The Recommendations on effects of the atmosphere (radiometeorology) are largely based on scientific studies carried out over a large pe
29、riod of time. They are developed from consensus among the delegates regarding the general knowledge on the subject. Since such knowledge is always developing and never reaches a final state, it is of prime importance to be able to keep track of the results of scientific studies on which the Recommen
30、dations are based. If that infomation is lost it is no longer possible to revisit the subjects treated by the Recommendations and improve these for the benefit of the users. Also, reviewing the background information may help the user to appreciate the limitations and accuracy of the models given. S
31、ince our understanding of the physics of radiowave propagation is limited, it is inevitable that the user will encounter questions that cannot be answered within the region of validity of the models presented in the Recommendations. In order to assist the user of the Recommendations and to give him
32、guidance when general answers cannot be given, this Handbook provides background information as well as up-to-date summaries of experimental results and preliminary results of further modelling. It is for this purpose that this Handbook on Radiometeorology has been prepared by ITU-R Study Group 3 (R
33、adiowave Propagation). It should serve both the users inside and outside the Study Group and the members of the Study Group in charge of the development of Recommendations on the effects of the troposphere on radiowave propagation. Purpose of the Handbook on Radiometeorology 1.2 Applicable texts The
34、 Recommendations on radiometeorology and statistical modelling methods for which Working Party 35 (Propagation fundamentals) is responsible and to which this Handbook provides background information, are listed below (situation as per January 1995). Recommendation ITU-R P.369-6 Recommendation ITU-R
35、P.453-4 Recommendation ITU-R P.834-1 Recommendation ITU-R P.83 5- 1 Recommendation ITU-R P.836 Recommendation ITU-R P.676-1 Reference atmosphere for rehction The radio refractive index: its formula and refkactivity data Effects of tropospheric refraction on radiowave propagation Reference standard a
36、tmosphere for gaseous attenuation Surface water vapour density Attenuation by atmospheric gases in the frequency range 1 - 350 GHz Recommendation ITU-R P. 83 7- 1 Recommendation ITU-R P.838 Characteristics of precipitation for propagation modelling Specific attenuation model for rain for use in pred
37、iction methods N:BRSGBSG3HANDBKl. WW6 4855212 0543b53 b95 D -2- Recommendation ITU-R P.839 Recommendation ITU-R P.840-1 Recommendation ITU-R P.58 1-2 Recommendation ITU-R P.84 i Recommendation ITU-R P.678-1 Recommendation ITU-R P. 1057 Recommendation ITU-R P.372-6 Rain height model for prediction me
38、thods Attenuation due to clouds and fog The concept of “worst month“ Conversion of annual statistics to worst-month statistics Characterization of the natural variability of propagation phenomena Probability distributions relevant to radiowave propagation modelling Radio noise (NOTE - The Handbook (
39、in particular Chapter 8) applies only to the part of Recommendation ITU-R P.372-6 (Radio noise) treating tropospheric noise emission.) 1.3 Cross-reference table The following table providing cross references between the chapters of the Handbook and the Recommendations may be useful in finding the ap
40、plicable texts. TABLE 1.1 Relation between Chapters and Recommendations N:BRSGBSG3“DBKl .WW6 4855232 0543b52 523 -3- CHAPTER 2 Physical characteristics of the atmosphere 2.1 Recommendation ITU-R P.835 provides information on the average atmosphere for the calculation of attenuation by atmospheric ga
41、ses, notably oxygen and water vapour. This section discusses the variability of the gases. Recommendation ITU-R P.836 gives monthly mean values of water vapour density for the world for the months of August and February Bean and Dutton, 19661. Maps of water vapour density for the months of February
42、and August have also been developed for the Peoples Republic of China CCIR, 1982-861. The relationships between water vapour density, p, water vapour pressure and relative humidity are given in Recommendation ITU-R P.453. Water vapour density is highly variable. To a first approximation, the tempora
43、l fluctuations of p may be assumed to follow a normal law with a standard deviation about one quarter the mean value. It is noted that the statistical variation of water vapour density is affected by atmospheric temperature. The relative humidity rarely reaches 100 per cent implying that the maximum
44、 water vapour density will not exceed the value corresponding to saturation at the atmospheric temperature. The water vapour density increases to a value near saturation in clouds and rainfall. At fiequencies above about 15 GHz the correlation between attenuation produced by water vapour absorption
45、and that produced by rain should be taken into account when estimating attenuation statistics or in interference calculations. In general, rain occurs during the season with the highest average values of water vapour density near the surface and the higher values of rain rate should be correlated wi
46、th the higher seasonal water vapour density values. As a first approximation for each location the higher value of water vapour density from Figures 1 and 2 of Recommendation ITU-R P.836 should be used for rain rates in excess of 25 mm/h and the lower value for lower rain rates. Statistical analysis
47、 of absolute humidity data for 62 sites in the United Kingdom indicates that the water vapour density exceeded for 0.1% and 99.9% of the time is approximately 15 g/m3 and 2.2 g/m3 respectively, with values approximately 10% larger in the south and 10% smaller in north- east Scotland yuK Meteorology
48、Office, 19761. Variability of water vapour and oxygen density at ground level 2.2 The dependence of water vapour density on height (the so-called “height profile“) is highly variable also. Recommendation ITU-R P.835 gives an average profile for use in general prediction methods. Variability of the h
49、eight profile of water vapour 2.3 Precipitation characteristics 2.3.1 Drop size distribution The size, shape and orientation distributions of raindrops may vary within a storm. Observations show that on average, the drop size distribution is relatively stable, changing mainly with rain rate. N:BRSGBSG3“DBKl. WW6 4855232 0543b53 Yb4 -4- The Laws and Parsons 19431 drop size distribution has been found useful for the estimation of the attenuation and scattering properties of rain at frequencies up to about 40 GHz. The relative densities of small drops having diam
