1、 Recommendation ITU-R P.836-6 (12/2017) Water vapour: surface density and total columnar content P Series Radiowave propagation ii Rec. ITU-R P.836-6 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum
2、by 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 Conf
3、erences 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
4、and 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 availab
5、le 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 se
6、rvices 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
7、frequency 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 wh
8、atsoever, without written permission of ITU. Rec. ITU-R P.836-6 1 RECOMMENDATION ITU-R P.836-6 Water vapour: surface density and total columnar content (Question ITU-R 201/3) (1992-1997-2001-2001-2009-2013-2017) Scope This Recommendation provides methods to predict the surface water vapour density a
9、nd total columnar 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
10、locations 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 accura
11、te local data 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; how
12、ever, the 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 ar
13、e available in the form of digital maps and are provided in the Supplement file R-REC-P.836-6-201712-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 Recommendat
14、ion and are available in the form of digital maps provided in the Supplement file. 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 the surface of the Earth ca
15、n be derived by the following interpolation method (if local data for the height above mean sea level at the desired location is not available, the map in Recommendation ITU-R P.1511 can be used): 2 Rec. ITU-R P.836-6 a) determine the two probabilities, pabove and pbelow, above and below the desired
16、 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, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for monthly statistics; b) for the two probabilities, pabove and pbelow, determine the surface wate
17、r 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 corresponding to the probabilities pabove and pbelow, determine the water vapour scale height at the four closest grid point, vsch1, vsch2, vsch3 and vsch4 for
18、each probability, pabove and pbelow; d) using the TOPO_0DOT5.txt topographic altitude digital map that is an integral part of this Recommendation and is provided in the Supplement file, determine the topographic altitudes, alt1, alt2, alt3 and alt4, at the four closest grid points using the bicubic
19、interpolation method specified in Annex 1 of Recommendation ITU-R P.1144; e) for each of the four closest grid points and each probability, determine the water vapour densities, 1, 2, 3 and 4, at the desired altitude, alt, by scaling the water vapour densities, 1 , 2 , 3 and 4 , using the following
20、relation: for i = 1, 2, 3, 4 (1) f) determine the water vapour densities, above and below, at the probabilities pabove and pbelow and at the desired location by performing a bi-linear interpolation of the four values of water vapour density, 1, 2, 3 and 4, at the four grid points as described in Rec
21、ommendation ITU-R P.1144 (for reference the procedure to determine above and below from 1 , 2 , 3 and 4 is shown in Fig. 1); g) determine the water vapour density, , at the desired probability, p, by interpolating above and below vs. pabove and pbelow to p on a linear vs. log p scale. For reference,
22、 the relationships between water vapour density, water vapour pressure and relative humidity are given in Recommendation ITU-R P.453. ivsch ialtaltii eRec. ITU-R P.836-6 3 FIGURE 1 Interpolation procedure at probabilities above and below desire probability P .08 36 -01S c a l e t o d e s i r e d a l
23、 t i t ude2 2a t gr i d p oi nt ( )al tS c a l e t o d e s i r e d a l t i t udeD e s i r e d a l t i t ude ( )al tB i - l i ne a r l y i nt e r pol a t e t o t he de s i r e d l a t i t ude , l ong i t ude a nd a l t i t udef r om t he f our gr i d p oi nt s s c a l e d t o t he s a m e a l t i t u
24、deS c a l e t o d e s i r e d a l t i t udeS c a l e t o d e s i r e d a l t i t ude1 1a t gr i d p oi nt ( )al t4 4a t gr i d p oi nt ( )al t3 3a t gr i d p oi nt ( )al t1342Annex 2 1 Total water vapour content For some applications, the total water vapour content along a path can be used for the c
25、alculation 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 specific mass absorption coefficient. The total water vapour content, expressed
26、in kg/m2 or, 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 time resolution and is only applicable to zenith paths. The total water vap
27、our 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, 20, 30, 50, 60, 70, 80, 90, 95 and 99% of the year are an integral part
28、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 month are an integral part of this Recommendation and are available in the
29、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 the Earth can be derived by the following interpolation method (if local da
30、ta for the height above mean sea level at the desired location is not available, the map in Recommendation ITU-R P.1511 can be used): 4 Rec. ITU-R P.836-6 a) determine the two probabilities, pabove and pbelow, above and below the desired probability, p, from the set: 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5,
31、10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for annual statistics and from the set: 1, 2, 3, 5, 10, 20, 30, 50, 60, 70, 80, 90, 95 and 99% for monthly statistics; b) for the two probabilitis, pabove and pbelow, determine the total columnar water vapour content, 1V , 2V , 3V and 4V at the four closest
32、 grid points; c) using the annual or the monthly water vapour scale height corresponding to the probabilities pabove and pbelow, determine the water vapour scale height at the four closest grid points, vsch1, vsch2, vsch3, and vsch4 for each probability, pabove and pbelow; d) using the TOPO_0DOT5.tx
33、t topographic altitude digital map that is an integral part of this Recommendation and is provided in the Supplement file, determine the topographic altitudes, alt1, alt2, alt3, and alt4, at the four closest grid points using the bicubic interpolation method specified in Annex 1 of Recommendation IT
34、U-R P.1144; e) for each of the four closest grid points and each probability, determine the total columnar water vapour content, V1, V2, V3 and V4, at the desired altitude, alt, by scaling the total columnar water vapour content, 1V , 2V , 3V and 4V , using the following relation: for i = 1, 2, 3, 4
35、 (2) f) determine the total columnar water vapour content, Vabove and Vbelow, at the probabilities pabove and pbelow and at the desired location by performing a bi-linear interpolation of the four values of total columnar water vapour content, V1, V2, V3 and V4, at the four grid points as described
36、in Recommendation ITU-R P.1144 (for reference the procedure to determine Vabove and Vbelow from 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 Vabove and Vbelow vs. pabove and pbelow to p on a linear V
37、 vs. log p scale. FIGURE 2 Interpolation procedure at probabilities above and below desired probability P .08 36 -02V al t2 2a t g r i d p o i n t ( )S c a l e t o d e s i r e d a l t i t u d eD e s i r e d a l t i t u d e ( )a l tB i - l i n e a r l y i n t e r p o l a t e V t o t h e d e s i r e d
38、 l a t i t u d e , l o n g i t u d e , a n d a l t i t u d e f r o m t h e f o u r g r i d p o i n t s s c a l e d t o t h e s a m e a l t i t u d eVV2S c a l e t o d e s i r e d a l t i t u d eS c a l e t o d e s i r e d a l t i t u d eS c a l e t o d e s i r e d a l t i t u d eV4V1V3V al t1 1a t g r i d p o i n t ( )V al t4 4a t g r i d p o i n t ( )V al t3 3a t g r i d p o i n t ( )ivsch ialtaltii VV e
