1、 Recommendation ITU-R M.1849-1 (09/2015) Technical and operational aspects of ground-based meteorological radars M Series Mobile, radiodetermination, amateur and related satellite services ii Rep. ITU-R M.1849-1 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable,
2、 efficient and economical use of the radio-frequency spectrum 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 Sect
3、or are performed by World and Regional Radiocommunication Conferences 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-
4、R 1. Forms to be used for the submission of patent statements 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 ca
5、n also be found. Series of ITU-R Recommendations (Also available 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
6、M Mobile, radiodetermination, amateur and related satellite 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 Spectru
7、m management SNG Satellite news gathering TF Time signals and 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, 2015 ITU 2015 All rights reserved.
8、No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R M.1849-1 1 RECOMMENDATION ITU-R M.1849-1* Technical and operational aspects of ground-based meteorological radars (2009-2015) Scope This Recommendation addresses the important techni
9、cal and operational characteristics of meteorological radars, describes the related products provided, highlights their major specificities, discusses the effects of interference on meteorological radars and develops related interference protection criteria. This text is limited to ground-based weat
10、her radars and does not include wind profiler radars, also used for meteorological purposes, which are covered in a separate ITU-R Recommendation. Keywords Radar, meteorological, protection Abbreviations/Glossary CASA Centre for collaborative adaptive sensing of the atmosphere GC Ground clutter Pd P
11、robability of detection PRF Pulse repetition frequency PRT Pulse repetition time SAR Synthetic aperture radar VAD Vertical azimuth display VCP Volume coverage pattern WTC Wind turbine clutter The ITU Radiocommunication Assembly, considering a) that antenna, signal propagation, target detection, and
12、large necessary bandwidth characteristics of radar to achieve their functions are optimum in certain frequency bands; b) that representative technical and operational characteristics of meteorological radars are required to determine the feasibility of introducing new types of systems into frequency
13、 bands in which meteorological radars are operated; c) that procedures and methodologies are needed to analyse compatibility between meteorological radars and other services to which the frequency band is allocated; d) that technical and operational characteristics of meteorological radars are speci
14、fic compared to other radar types and justify a separate ITU-R Recommendation; * This Recommendation should be brought to the attention of the World Meteorological Organization (WMO). 2 Rep. ITU-R M.1849-1 e) that meteorological radars mainly operate in the frequency bands 2 700-2 900 MHz, 5 250-5 7
15、25 MHz and 9 300-9 500 MHz; f) that meteorological radars are key observation stations used for meteorological observing and environmental monitoring; g) that meteorological radars play a crucial role in providing warnings of imminent severe weather conditions, such as flooding, cyclones and hurrica
16、nes, that can endanger populations and damage strategic economic infrastructure; h) that the application of protection criteria requires consideration for inclusion of the statistical nature of the criteria and other elements of the methodology for performing compatibility studies (e.g. antenna scan
17、ning and propagation path loss). Further development of these statistical considerations may be incorporated into future revisions of this Recommendation, as appropriate, recognizing a) that No. 5.423 of the Radio Regulations (RR) states that ground-based meteorological radars in the frequency band
18、2 700-2 900 MHz are authorized to operate on a basis of equality with stations of the aeronautical radionavigation service; b) that RR No. 5.452 states that ground-based meteorological radars in the frequency band 5 600-5 650 MHz are authorized to operate on a basis of equality with stations of the
19、maritime radionavigation service; c) that RR No. 5.475B states that ground-based meteorological radars in the frequency band 9 300-9 500 MHz have priority over other radiolocation uses, noting a) that Recommendation ITU-R M.1461 is also used as a guideline in analysing the compatibility between rada
20、rs and other services to which the frequency band is allocated; b) that radar protection criteria depend on the specific types of interfering signals, such as those described in Annex 1, recommends 1 that the technical and operational aspects of meteorological radars described in Annex 1 and the cha
21、racteristics given in Annex 2 should be considered when conducting sharing studies; 2 that the aggregate protection criteria for ground-based meteorological radars should be an I/N of 10 dB. Annex 1 Technical and operational aspects of ground-based meteorological radars 1 Introduction Ground-based m
22、eteorological radars are used for operational meteorology and weather prediction, atmospheric research, and aeronautical and maritime navigation, and play a crucial role in the immediate meteorological and hydrological alert processes. These radars are also in operation Rec. ITU-R M.1849-1 3 continu
23、ously 24 h/day. Meteorological radar networks represent the last line of detection of weather that can cause loss of life and property in flash flood or severe storms events. The theory of operation and the products generated by meteorological radars are remarkably different from other radars. These
24、 differences are important to understand when evaluating the compatibility between meteorological radars and other services to which the frequency band is allocated. The technical and operational characteristics of meteorological radars result in different effects from permissible interference in co
25、mparison to other radar systems. 2 Overview Meteorological radars are used to sense the conditions of the atmosphere for routine forecasting, severe weather detection, wind and precipitation detection, precipitation estimates, detection of aircraft icing conditions and avoidance of severe weather fo
26、r navigation. Meteorological radars transmit horizontally polarized pulses which measure the horizontal dimension of a cloud (cloud water and cloud ice) and precipitation (snow, ice pellets, hail and rain particles). Polarimetric radars, also called dual-polarization radars, transmit pulses in both
27、horizontal and vertical polarizations. These radars provide significant improvements in rainfall estimation, precipitation classification, data quality and weather hazard detection over non-polarimetric systems. Meteorological radars are not an individual radio service within the ITU-R, but fall und
28、er the radiolocation and/or radionavigation service in the RR. The determination of whether radiolocation and/or radionavigation apply depends on how the particular radar is used. A ground-based meteorological radar used for atmospheric research or weather forecasting would be operated under the rad
29、iolocation service. Airborne meteorological radar on a commercial aircraft would operate under the radionavigation service. A ground-based meteorological radar can also operate under the radionavigation service if, for example, it is used by air traffic control for routing aircraft around severe wea
30、ther. As a result, meteorological radars could operate in a variety of allocated radiolocation and radionavigation frequency bands, as long as the use is consistent with the radio service definition. The RR contain three specific references to meteorological radars in the Table of Frequency Allocati
31、ons. The three references are contained in footnotes associated with the frequency bands 2 700-2 900 MHz (RR No. 5.423), 5 600-5 650 MHz (RR No. 5.452) and 9 300-9 500 MHz (RR No. 5.475). 2.1 Radar equation for single target1 Meteorological radars do not track point targets. However, the radar equat
32、ion can be adapted to be used with meteorological radars. The amount of power returned from a volume scan performed by the meteorological radar determines if weather phenomena will be detectable. The radar range equation expresses the relationship between the power returned from a target, and charac
33、teristics of the particular target and the transmitting radar. The typical point target will have the following radar equation variables: PR: received power by the radar PT: radar peak transmit power AT: area of target R: range of target from radar 1 Information and derivation of the equations in th
34、ese sections is found in YAU, M. K. and ROGERS, R. R. 1 January 1989 A Short Course in Cloud Physics, Chapter 11. 4 Rep. ITU-R M.1849-1 G: gain of the transmit antenna. These variables combine to create the general radar equation for a point target: TTR ArGPP 43224The above equation assumes isotropi
35、c radiation and an isotropic scatter. However, most targets do not scatter incident radiation isotropically, and thus the backscatter cross-section, , of the target is necessary: 43 224 rGPP TR 2.2 Meteorological radar equation With the equation for a single-point target derived, the next step is to
36、 edit the equation above to account for meteorological radar targets. Raindrops, snowflakes and cloud droplets are examples of an important radar class of targets, known as distributed targets. The incident radar pulse creates the transmitted resolution volume of the meteorological radar by simultan
37、eously illuminating the volume containing weather particles. The mean power received from weather targets results in the equation below, where is the sum of the backscatter cross-sections of all the particles within the resolution volume. nTR rGPP 43 224 Since the volume of the radar beam continues
38、to expand with increasing range, the radar beam includes more and more targets. The defined volume of the radar beam is equivalent to: 222 hrV where h = c is the pulse length and is the antenna beamwidth. By combining the general radar equation with the volume of the radar beam, the mean power retur
39、ned becomes: 22424322 hrrGPP TR where denotes the radar reflectivity per unit volume. The above equation, however, assumes the antenna gain is uniform within its 3 dB limits, which is untrue. By assuming a Gaussian beam pattern, the effective volume is more appropriately defined over the radar beam
40、pattern, instead of within the 3 dB limits. Using a Gaussian beam pattern, the mean power returned becomes: Rec. ITU-R M.1849-1 5 22222)2(1n0241 rhGPP TR By accounting for a single spherical particle that is small compared to the radar wavelength, the backscatter cross section can be represented by
41、= 64 5/4|K|2ro2, where K is the complex index of refraction and ro represents the sphere radius. Weather particles small enough for the Rayleigh scattering law to apply are known as Rayleigh scatterers. Raindrops and snowflakes are considered Rayleigh scatterers measured to accurate approximation wh
42、en the radar wavelength is between 5 cm and 10 cm, common operating wavelengths for weather radars. At a 3 cm wavelength, the approximate scattering can still be useful, but is less accurate. For a group of spherical drops, which are small compared to the radar wavelength, the average returned power
43、 changes to: n oTR rKrGPP 624543 22 644 where is a summation of the spherical radius for each the weather scatterers. By allowing (D/2)6 to equal 6or , the mean power returned can be reflected in terms of drop diameters for spherical scatterers: nTR DKrGPP 622543 24 Thus for spherical scatterers tha
44、t are considerably smaller than the radar wavelength, the mean power received by the weather radar is determined by the radar characteristics, range, the scatterer index of refraction (|K|2), and the diameter of the scatterer (D6). Finally, the target reflectivity factor, Z, can be introduced as Z =
45、 V D6 = N(D)D6dD, where V is the summation over a unit volume and N(D)D6 is the number of scatterers per unit volume. The final form of the radar equation for weather radars, including the corrections made previously to represent a Gaussian beam pattern, results in: 222223)2(1n0241 rZKGPcP TR3 Gener
46、al meteorological radars principles Meteorological radars primarily perform two types of measurements: precipitation measurements; wind measurements. These measurements are performed over pixel grids that allow presenting cartography of the above-mentioned meteorological events. 3.1 Example of meteo
47、rological radar operation in the frequency band 2.7-2.9 GHz Radar 1 in Annex 2, Table 1 is a system representative of meteorological radars operated at frequencies around 2.8 GHz. The 0 dBz curve for this radar intersects the receiver noise level (113 dBm) at a range of 200 km. 6 Rep. ITU-R M.1849-1
48、 3.1.1 Precipitation estimation Representative radars operated near 2.8 GHz use a variety of reflectivity-range (Z-R) and reflectivity- rainfall-rate (Z-S) formulas for precipitation estimation. Depending on the specific algorithm, the effect of interference on operational range can vary. Example of
49、 meteorological radar operation in the frequency band 5.6-5.65 GHz On a typical basis, radar coverage extends over 200 km, presenting a pixel resolution of 1 km 1 km. In some instances, a more detailed grid is presented over 250 m 250 m pixels. For each pixel, the radar measurements are calculated over all the pulse responses corresponding to this pixel, i.e. for each pulse pair
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