1、 Recommendation ITU-R P.837-7 (06/2017) Characteristics of precipitation for propagation modelling P Series Radiowave propagation ii Rec. ITU-R P.837-7 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectru
2、m 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 Co
3、nferences 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 statement
4、s 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 avail
5、able 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
6、services 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 an
7、d 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
8、whatsoever, without written permission of ITU. Rec. ITU-R P.837-7 1 RECOMMENDATION ITU-R P.837-7 Characteristics of precipitation for propagation modelling (Question ITU-R 201/3) (1992-1994-1999-2001-2003-2007-2012-2017) Scope Rainfall rate statistics with a 1-min integration time are required for t
9、he prediction of rain attenuation in terrestrial links (e.g. Recommendation ITU-R P.530) and Earth-space links (e.g. Recommendation ITU-R P.618). When reliable long-term local rainfall rate data is not available, Annex 1 of this Recommendation provides a rainfall rate prediction method for the predi
10、ction of rainfall rate statistics with a 1-min integration time. This prediction method is based on: a) total monthly rainfall data generated from the GPCC Climatology (V 2015) database over land and from the European Centre for Medium-Range Weather Forecast (ECMWF) ERA Interim re-analysis database
11、over water, and b) monthly mean surface temperature data in Recommendation ITU-R P.1510. When reliable long-term local rainfall rate data is available with integration times greater than 1-min, Annex 2 of this Recommendation provides a method for converting rainfall rate statistics with integration
12、times that exceed 1-min to rainfall rate statistics with a 1-min integration time. Keywords Rainfall rate, annual statistics, conversion method, GPCC, ERA Interim The ITU Radiocommunication Assembly, considering a) that information on the yearly statistics of precipitation parameters are needed for
13、the prediction of attenuation and scattering caused by precipitation; b) that the information is needed for all locations on the surface of the Earth and a wide range of probabilities; c) that rainfall rate statistics with a 1-min integration time are required for the prediction of rain attenuation
14、and scattering in terrestrial and satellite links; d) that long-term measurements of rainfall rate may be available from local sources with a 1-min integration time and, also, with integration times that exceed 1-minute; e) that using a model to convert local rainfall rate measurements with integrat
15、ion times up to 1 hour into an integration time of 1-minute may provide higher accuracy than Annex 1 of this Recommendation, recommends 1 that local long-term measurements of annual rainfall rate with a 1-minute integration time should be used if available; 2 that local measurements, if used, are co
16、llected over a sufficiently long period of time (typically longer than 10 years), to ensure statistical stability; 2 Rec. ITU-R P.837-7 3 that long-term measurements of annual rainfall rate with integration times that exceed 1 minute should be used if available, and the conversion method in Annex 2
17、should be used to convert these measurements to annual rainfall rate with a 1-minute integration time; 4 that, in the absence of reliable local rainfall rate data, the step-by-step prediction method in Annex 1 should be used to obtain the rainfall rate, Rp, exceeded for the desired annual probabilit
18、y of exceedance, p, for any location on the surface of the Earth, and for an integration time of 1 minute. Annex 1 Prediction method to derive the rainfall rate exceeded for a given average annual probability of exceedance and given location This prediction method calculates the rainfall rate exceed
19、ed for a desired average annual probability of exceedance and a given location on the surface of the Earth using digital maps of monthly total rainfall and monthly mean surface temperature. The monthly mean total rainfall maps were derived from 50 years (1951-2000) of data from the GPCC Climatology
20、(V 2015) database over land and from 36 years (1979-2014) of the European Centre of Medium-range Weather Forecast (ECMWF) ERA Interim data over water. The monthly mean total rainfall data, MTii (mm), where ii = 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11 and 12, are an integral part of this Recommend
21、ation and are available as digital maps. The latitude grid is from 90.125 N to +90.125 N in 0.25 steps, and the longitude grid is from 180.125 E to +180.125 E in 0.25 steps. The annual rainfall rate data exceeded for 0.01% of an average year, R0.01 (mm/hr), is also an integral part of this Recommend
22、ation and are available as digital maps. The latitude grid is from 90 N to +90 N in 0.125 steps, and the longitude grid is from 180 E to +180 E in 0.125 steps. These digital maps are available in the Supplement file R-REC-P.837-7-Maps.zip. Input parameters: p: Desired annual probability of exceedanc
23、e (%) Lat: Latitude of the desired location (degrees, N) Lon: Longitude of the desired location (degrees, E) Output parameter: Rp: Rainfall rate exceeded for the desired probability of exceedance (mm/h). Step 1: For each month of the year, define the month number, ii, and the number of days in each
24、month, iiN , as follows: Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec ii 01 02 03 04 05 06 07 08 09 10 11 12 Nii 31 28.25 31 30 31 30 31 31 30 31 30 31 Rec. ITU-R P.837-7 3 Step 2: For each month number, ii, where ii = 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11 and 12, determine the monthly
25、 mean surface temperatures, Tii (K), at the desired location (Lat, Lon) from reliable long-term local data. If reliable long-term local data is not available, the monthly mean surface temperatures, Tii (K), at the desired location (Lat, Lon) can be obtained from the digital maps of monthly mean surf
26、ace temperature in Recommendation ITU-R P.1510. Step 3: For each month number ii, where ii = 01, 02, 03, 04, 05, 06, 07, 08, 09, 10, 11 and 12, determine the monthly mean total rainfall, MTii (mm), at the desired location (Lat, Lon) from reliable long-term local data. If reliable long-term local dat
27、a is not available, the monthly mean total rainfall at the desired location (Lat, Lon) can be determined from the digital maps of monthly mean total rainfall, MTii (mm), provided as an integral part of this Recommendation as follows: a) determine the four grid points (Lat1, Lon1), (Lat2, Lon2), (Lat
28、3, Lon3) and (Lat4, Lon4) surrounding the desired location (Lat, Lon); b) determine the monthly mean total rainfall, 1,iiMT , 2,iiMT , 3,iiMT , and 4,iiMT at the four surrounding grid points of the maps provided with this Recommendation; c) determine iiMT at the desired location (Lat, Lon) by perfor
29、ming a bi-linear interpolation using the four surrounding grid points as described in Annex 1 Paragraph 1b of Recommendation ITU-R P.1144. Step 4: For each month number, ii, convert Tii (K) to tii (C). Step 5: For each month number, ii, calculate rii as follows: 5874.0 5874.00883.0iitiir erii Ctfor
30、Ctforiiii 00 )/( hrmm (1) Step 6a:For each month number, ii, calculate the monthly probability of rain as follows: 0 = 100 24 (%) (2) Step 6b:For each month number, ii, if 700 iiP, set 700 iiPand iiiiii NMTr 2470100 Step 7: Calculate the annual probability of rain, 00 RPPannualas follows: 25.365121
31、00 ii ii iiannualPNP(%) (3) Step 8: If the desired rainfall rate probability of exceedance, p, is greater than annualP0, the rainfall rate at the desired rainfall rate probability of exceedance, , is 0 mm/hr. If the desired rainfall rate probability of exceedance, p, is less than or equal to annualP
32、0, adjust the rainfall rate, Rref, until the absolute value of the relative error between the annual rainfall rate probability of exceedance, refRRP , and the desired rainfall rate probability of exceedance, p, is less than 0.001% (i.e. until 100|() 1| 0.001), where: 4 Rec. ITU-R P.837-7 25.365121ii
33、 r e fiiiir e fRRPNRRP (%) (4) 26.1 ln7938.0ln0 iir e fr e fii rRQPRRPii(%) (5) and dtexQxt 2221 (6) At the end of the adjustment process, set Rp = Rref. NOTE 1 When the 0.01% average annual probability of exceedance is required, and where memory and computational complexity are considerations, the
34、pre-computed map of 0.01 can be used with insignificant loss in accuracy. If this map is used, the rainfall rate at the 0.01% average annual probability of exceedance at any desired location on the surface of the Earth can be calculated by performing a bi-linear interpolation using the method descri
35、bed in Annex 1 Paragraph 1b of Recommendation ITU-R P.1144. The absolute value of the difference between the full rainfall rate prediction method and the pre-computed 0.01 map is less than 0.3 mm/hr for greater than 99.9% of the surface of the Earth, and the absolute value of the difference between
36、the full rainfall rate prediction method and the 0.01 map is less than 1 mm/hr for greater than 99.99% of the surface of the Earth. NOTE 2 When the 0.01% average annual probability of exceedance is required using the full rainfall rate prediction method, the pre-computed map of 0.01, the rainfall ra
37、te at the 0.01% exceedance probability could be used as the initial starting point Rref for the iterative procedure in Step 8. For reference, a map of R0.01, the annual rainfall rate exceeded for 0.01% of an average year, is shown in Fig. 1. Rec. ITU-R P.837-7 5 FIGURE 1 Rainfall rate exceeded for 0
38、.01% of an average year P.0837-019060180120Longitude()ELitude at() N753045 0153015604590756104106001080040202040608010012014016018001020304050607080906 Rec. ITU-R P.837-7 Annex 2 1 The cumulative distribution of rainfall rate at 1-min integration time can be obtained by converting local cumulative d
39、istributions measured at integration times of between 5 and 60 minutes. 2 The recommended method requires as input both the cumulative distribution as well as the integration time of the source rainfall statistics and the geographical coordinates of the site of interest. 3 The method is based on the
40、 simulated movement of synthetic rain cells, whose parameters derive from the local input data and ECMWF products. 4 The recommended method is incorporated in a computer program available at the Supplement. The name of the software package implementing this part of the Recommendation is R-REC-P.837-7-Convrrstat.zip.
