1、 Recommendation ITU-R P.836-5(09/2013)Water vapour: surface density and total columnar contentP SeriesRadiowave propagationii Rec. ITU-R P.836-5 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by al
2、l 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 Conferenc
3、es 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 and l
4、icensing 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 on
5、line 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 service
6、s 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 frequ
7、ency 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, 2013 ITU 2013 All rights reserved. No part of this publication may be reproduced, by any means whatsoe
8、ver, without written permission of ITU. Rec. ITU-R P.836-5 1 RECOMMENDATION ITU-R P.836-5 Water vapour: surface density and total columnar content (Question ITU-R 201/3) (1992-1997-2001-2001-2009-2013) Scope This Recommendation provides methods to predict the surface water vapour density and total c
9、olumnar water vapour content on Earth-space paths. The ITU Radiocommunication Assembly, considering a) that for the calculation of refractive effects and gaseous attenuation, information on the water vapour density of the atmosphere is needed; b) that this information is available for all locations
10、on the Earth and for all seasons, recommends that the information in Annexes 1 and 2 should be used for global calculations of propagation effects that require an estimate of surface water vapour density or total columnar content of water vapour and its seasonal variation, when more accurate local d
11、ata are not available. Annex 1 1 Surface water vapour density Atmospheric water vapour and oxygen cause absorption at millimetre wavelengths especially in the proximity of absorption lines (see Recommendation ITU-R P.676). The concentration of atmospheric oxygen is relatively constant; however, the
12、concentration of water vapour varies both geographically and with time. The annual values of surface water vapour density, in g/m3, exceeded for 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95, and 99% of an average year are an integral part of this Recommendation and are availabl
13、e in the form of digital maps and are provided in the file R-REC-P.836-5-201309-I!ZIP-E. The monthly values of surface water vapour density, in g/m3, exceeded for 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95, and 99% of an average month are an integral part of this Recommendation and are available
14、 in the form of digital maps and are provided in the file R-REC-P.836-5-201309-I!ZIP-E. 2 Rec. ITU-R P.836-5 The data is from 0 to 360 in longitude and from +90 to 90 in latitude, with a resolution of 1.125 in both latitude and longitude. The surface water vapour density at any desired location on t
15、he surface of the Earth can be derived by the following interpolation method: a) determine the two probabilities, paboveand pbelow, above and below the desired probability, p, from the set: 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for annual statistics and from the
16、set: 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for monthly statistics; b) for the two probabilities, paboveand pbelow, determine the surface water vapour densities, 1 , 2 , 3 and 4 at the four closest grid points; c) using the annual or the monthly water vapour scale height data file co
17、rresponding to the probabilities paboveand pbelow, determine the water vapour scale height at the four closest grid point, vsch1, vsch2, vsch3and vsch4for each probability, paboveand pbelow; d) using Recommendation ITU-R P.1511, determine the topographic altitudes, alt1, alt2, alt3and alt4, of the f
18、our closest grid points; e) for each of the four closest grid points and each probability, determine the water vapour densities, 1, 2, 3and 4, at the desired altitude, alt, by scaling the water vapour densities, 1 , 2 , 3 and 4 , using the following relation: for i = 1, 2, 3, 4 (1) f) determine the
19、water vapour densities, aboveand below, at the probabilities paboveand pbelowand at the desired location by performing a bi-linear interpolation of the four values of water vapour density, 1, 2, 3and 4, at the four grid points as described in Recommendation ITU-R P.1144 (for reference the procedure
20、to determine aboveand belowfrom 1 , 2 , 3 and 4 is shown in Fig. 1); g) determine the water vapour density, , at the desired probability, p, by interpolating aboveand belowvs. paboveand pbelowto p on a linear vs. log p scale. For reference, the relationships between water vapour density, water vapou
21、r pressure and relative humidity are given in Recommendation ITU-R P.453. ivschialtaltii= eRec. ITU-R P.836-5 3 FIGURE 1 Interpolation procedure at probabilities above and below desire probability P.0836-01Scale to desired altitude2 2at grid point ( )altScale to desired altitudeDesired altitude ( )a
22、ltBi-linearly interpolate to the desired latitude, longitude and altitudefrom the four grid points scaled to the same altitudeScale to desired altitudeScale to desired altitude1 1at grid point ( )alt4 4at grid point ( )alt3 3at grid point ( )alt1342Annex 2 1 Total water vapour content For some appli
23、cations, the total water vapour content along a path can be used for the calculation of excess path length and for the attenuation due to atmospheric water vapour, where the attenuation due to atmospheric water vapour is assumed to be proportional to the total water vapour content through its specif
24、ic mass absorption coefficient. The total water vapour content, expressed in kg/m2or, equivalently, in mm of precipitable water, can be obtained from radiosonde soundings, navigation satellite measurements, and radiometric observations. Radiosonde data is widely available; however, it has limited ti
25、me resolution and is only applicable to zenith paths. The total water vapour content can be retrieved from radiometric measurements at appropriate frequencies along the desired path. The annual values of total columnar water vapour content, V (kg/m2), exceeded for 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5, 10,
26、 20, 30, 50, 60, 70, 80, 90, 95 and 99% of the year are an integral part of this Recommendation and are available in the form of digital maps. The monthly values of total columnar water vapour content, V (kg/m2), exceeded for 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95, and 99% of each average mo
27、nth are an integral part of this Recommendation and are available in the form of digital maps. The data is from 0 to 360 in longitude and from +90 to 90 in latitude, with a resolution of 1.125 in both latitude and longitude. The total water vapour content at any desired location on the surface of th
28、e Earth can be derived by the following interpolation method: a) determine the two probabilities, paboveand pbelow, above and below the desired probability, p, from the set: 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for annual statistics and from the set: 1, 2, 3, 5,
29、 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for monthly statistics; 4 Rec. ITU-R P.836-5 b) for the two probabilitis, paboveand pbelow, determine the total columnar water vapour content, 1V , 2V , 3V and 4V at the four closest grid points; c) using the annual or the monthly water vapour scale height
30、 corresponding to the probabilities paboveand pbelow, determine the water vapour scale height at the four closest grid points, vsch1, vsch2, vsch3, and vsch4for each probability, paboveand pbelow; d) using Recommendation ITU-R P.1511, determine the topographic altitudes, alt1, alt2, alt3, and alt4,
31、of the four closest grid points; e) for each of the four closest grid points and each probability, determine the total columnar water vapour content, V1, V2, V3and V4, at the desired altitude, alt, by scaling the total columnar water vapour content, 1V , 2V , 3V and 4V , using the following relation
32、: for i = 1, 2, 3, 4 (2) f) determine the total columnar water vapour content, Vaboveand Vbelow, at the probabilities paboveand pbelowand at the desired location by performing a bi-linear interpolation of the four values of total columnar water vapour content, V1, V2, V3and V4, at the four grid poin
33、ts as described in Recommendation ITU-R P.1144 (for reference the procedure to determine Vaboveand Vbelowfrom 1V , 2V , 3V and 4V is shown in Fig. 2); g) determine the total columnar water vapour content, V, at the desired probability, p, by interpolating Vaboveand Vbelowvs. paboveand pbelowto p on
34、a linear V vs. log p scale. FIGURE 2 Interpolation procedure at probabilities above and below desired probability P.0836-02Valt2 2at grid point ( )Scale to desired altitudeDesired altitude ( )altBi-linearly interpolate V to the desired latitude, longitude, and altitude from the four grid points scaled to the same altitudeVV2Scale to desired altitudeScale to desired altitudeScale to desired altitudeV4V1V3Valt1 1at grid point ( )Valt4 4at grid point ( )Val3 3at grid point ( )ivschialtaltiiVV= e
