Presentation on theme: "ITU/WMO Seminar “Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and Prediction” Session 6: Meteorological Radars 6.1.1."— Presentation transcript:
1ITU/WMO Seminar “Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and Prediction” Session 6: Meteorological Radars Weather RadarsPresented By:R.P LeckEarth Resource Technologies Inc.For : NOAA-National Weather ServiceSeptember 2009
2Meteorological Radars Agenda Weather RadarsFrequency BandsSystem OverviewOperationsData UtilizationImpact of InterferenceRelevant ITU DocumentsLooking ForwardConclusions
3Weather Radars Frequency Bands Weather Radar Frequency Bands Frequency band (MHz)Band Name2 700-2 900S-Band5 250-5 725(Mainly 5 600-5 650 MHz)C-Band9 300-9 500X-BandS band radars operate on a wavelength of 8-15 cm and a frequency of 2-4 GHz. Because of the wavelength and frequency, S band radars are not easily attenuated. This makes them useful for near and far range weather observation. The National Weather Service (NWS) uses S band radars on a wavelength of just over 10 cm. The drawback to this band of radar is that it requires a large antenna dish and a large motor to power it. It is not uncommon for a S band dish to exceed 25 feet in size.C band radars operate on a wavelength of 4-8 cm and a frequency of 4-8 GHz. Because of the wavelength and frequency, the dish size does not need to be very large. This makes C band radars affordable for TV stations. The signal is more easily attenuated, so this type of radar is best used for short range weather observation. The frequency allows C band radars to create a smaller beam width using a smaller dish. C band radars also do not require as much power as an S band radar. The NWS transmits at 750,000 watts of power for their S band, where as a private TV stations typically transmit 270,000 watts of power with their C band radar. There are some C-bands with 1 MW of transmit power.X band radars operate on a wavelength of cm and a frequency of 8-12 GHz. Because of the smaller wavelength, the X band radar is more sensitive and can detect smaller particles. These radars are used for studies on cloud development because they can detect the tiny water particles and also used to detect light precipitation such as snow. X band radars also attenuate very easily, so they are used for only very short range weather observation. Also, due to the small size of the radar, it can therefore be portable like the Doppler on Wheels. (DOW) Most major airplanes are equipped with an X band radar to pick up turbulence and other weather phenomenon. This band is also shared with some police speed radars and some space radars.
4Weather Radars System Overview S-Band Operate in the MHz BandIn the US, WSR-88Ds operate up to 3000 MHzTypical peak transmitter power is ~750 kW300 km RangeBest Severe Weather Performance159 operational S-Band NEXRAD Radars form the backbone of the US Severe Weather Warning SystemNEXRAD (Next-Generation Radar) is a network of 159 high-resolution Doppler weather radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce. Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988, Doppler. The WSR-88D Doppler radar (NEXRAD) represents the backbone of the severe weather warning system in the United States for both the National Weather Service (NWS) and Department of Defense (DoD). There are a total of 159 NEXRAD sites in the U. S., including Alaska, Guam, Hawaii, and Puerto Rico. In the US some of the WSR-88D’s operate at 3000 MHz.NEXRAD detects precipitation and atmospheric movement or wind. It returns data which when processed can be displayed in a mosaic map or individual site displays] which show patterns of precipitation and its movement. The radar system operates in two basic modes, selectable by the operator — a slow-scanning clear-air mode for analyzing air movements when there is little or no activity in the area, and a precipitation mode, with a faster scan for tracking active weather. NEXRAD has an increased emphasis on automation, including the use of algorithms and automated volume scans.
5Weather Radars System Overview C-Band (Commercial) Operates within the MHz Band (Primarily between MHz)Typical transmitter power is ~270 kW~200 km RangeC-Band System are widely deployed on a worldwide basisUsed by many TV StationsC band radars operate with the MHZ Band. They are typically deployed with the MHZ range. Because of the wavelength and frequency, the dish size does not need to be very large. This makes C band radars affordable for TV stations. The signal is more easily attenuated, so this type of radar is best used for short range weather observation. The frequency allows C band radars to create a smaller beam width using a smaller dish.C band radars do not typically require as much power as an S band radar. From an operational perspective, the actual transmitter power depends on range requirement. Most C Band system transmit at 270,000 watts of power but some transmit with as much as 1 MW. In comparison The NWS NEXRAD S Band radar transmits at 750,000 watts of power.
6Weather Radars System Overview C-Band (Government) FAA operates 45 Terminal Doppler Weather Radar (TDWR’s) systems at or near major airports in the USOperates within the MHz BandTypical transmitter power is ~270 kW~90 km RangeDetects hazardous weather conditions such as windshear, microbursts and gust fronts, tornadic winds and heavy precipitation (inferring thunderstorms at an airport)The Terminal Doppler Weather Radar (TDWR) is an advanced technology weather radar deployed near 45 of the larger airports in the U.S. The radars were developed and deployed by the Federal Aviation Administration (FAA) beginning in 1994, as a response to several disastrous jetliner crashes in the 1970s and 1980s caused by strong thunderstorm winds. The crashes occurred because of wind shear--a sudden change in wind speed and direction. Wind shear is common in thunderstorms, due to a downward rush of air called a microburst or downburst.The TDWR was designed by the FAA to look for low altitude phenomena such as wind shifts over the runways, wind shear along the immediate approach and departure corridors, and downbursts. Therefore these radars are typically located close to major airports, and the scanning strategy is optimized to sample the atmosphere over its associated airport.Terminal Doppler Weather Radar (TDWR) system detects hazardous weather conditions such as windshear, microbursts and gust fronts, tornadic winds, heavy precipitation (inferring thunderstorms at an airport). This weather information is provided to air traffic controllers on displays at terminal facilities
7Weather Radars System Overview X-Band Operates within the MHz BandTypical transmitter power is 100 W to 25 kW~50 km RangeElement of Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) networkUsers of X-Band Weather Radars include:TV stationsMilitaryResearchersSmall physical sizeLow Cost compared to S or C Band SystemsX band radars operate on a wavelength of cm and a frequency of 8-12 GHz. Because of the smaller wavelength, the X band radar is more sensitive and can detect smaller particles. These radars are used for studies on cloud development because they can detect the tiny water particles and also used to detect light precipitation such as snow. X band radars also attenuate very easily, so they are used for only very short range weather observation. Also, due to the small size of the radar, it can therefore be portable like the Doppler on Wheels. (DOW) Most major airplanes are equipped with an X band radar to pick up turbulence and other weather phenomenon. This band is also shared with some police speed radars and some space radars.NSSL is participating in an NSF-sponsored Engineering Research Center called the Center for Collaborative Adaptive Sensing of the Atmosphere (CASA) to explore sensing the lower atmosphere with a network of many short-wavelength (3cm) radars. These smaller and less expensive radars will be spaced much closer together than those in the current operational radar network to provide data in blind spots caused by terrain blockage and the curvature of the earth CASA will also employ a new observation methodology termed DCAS (Distributed Collaborative Adaptive Sensing), that will operate the network of radars collaboratively and adapt them to changing atmospheric conditions and the needs of various end users. DCAS benefits include: Significant reductions in tornado false-alarms, improved precipitation estimates for flood prediction, detection of humidity and temperature variables, an improved understanding of how winds carry chemical, radiological or biological hazards all of which will save lives and reduce property losses
8Weather Radars Operations US NEXRAD Network Started Service in June 1992159 Network Sites selected to provide overlapping coverageSuper Resolution Upgrade Began in June 2008 increased Doppler Data Range to 300 km from 230 kmProvides Nationwide Reflectivity MosaicGenerates multiples levels of data which include….Level II data - meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width.41 meteorological analysis products known as Level III data are generated from the Level II Data.The data are sent to the National Climatic Data Center (NCDC) for archiving and dissemination.A detailed description of these products can be found atNEXRAD data is also used in hydrology, ecology, and environmental studies.NEXRADNexrad (Next-Generation Radar) is a network of 159 high-resolution Doppler weather radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration (NOAA) within the United States Department of Commerce. Its technical name is WSR-88D, which stands for Weather Surveillance Radar, 1988, Doppler. NEXRAD detects precipitation and atmospheric movement or wind. It returns data which when processed can be displayed in a mosaic map which shows patterns of precipitation and its movement.Super resolutionIn the process of implementation from March to June 2008, is the capability of the RDA to produce super resolution data. The WSR-88D provides reflectivity data at 1 km by 1 degree to 460 km range, and Doppler data at 0.25 km by 1 degree to a range of 230 km. Super Resolution will provides data with a sample size of 0.25 km by 0.5 degree, and increase the range of Doppler data to 300 km. Initially the increased resolution will only be available in the lower scan elevations. Super resolution makes a compromise of slightly decreased noise reduction for a large gain in resolution.To improve severe weather warning lead times, potential tornadic storms need to be identified as soon as possible. The improvement in beam width resolution increases the range at which small tornado parent circulation patterns (down to 4 km diameter) can be detected. Super-resolution also provides additional detail to aid in severe storm analysis. Extending the range of Doppler data and providing Doppler data earlier in the process of a volume scan provides velocity data more quickly than current scan techniquesDataLevel II data are the three meteorological base data quantities: reflectivity, mean radial velocity, and spectrum width. Data are collected and recorded in units of files which typically contain five, six, or ten minutes of base data depending on the volume coverage pattern. A data file consists of a 24 byte volume scan header record followed by numerous 2432 byte base data and message records.There are a total of 41 Level-III products routinely available from NCDC. Most Level III products are available as digital images, color hard copy, gray scale hard copy or acetate overlay copies.real-time product data: and real-time Level II data:
9Weather Radars Operations 150 Weather Radars European Network (OPERA – Operational Program for the Exchange of weather RAdar information)150 Weather RadarsSupported Within the OPERA NetworkApproximately 100 Doppler RadarsDual-Polarization is becoming the operational standard.The fundamental objective of OPERA is to provide a European platform wherein expertise on operationally-oriented weather radar issues is exchanged and holistic management procedures are optimized. With the establishment of its Data Hub, OPERA is now organized to support the application of radar data from the European Weather Radar Network. Another important objective of OPERA is to act to harmonize data and product exchange at the European level.The OPERA programme (Operational Programme for the Exchange of weather Radar information, is the Weather Radar programme of EUMETNET, the Network of the European Meteorological Services (NMSs). The objective of OPERA is to harmonize and improve the operational exchange of weather radar information between national meteorological services. The third phase of the OPERA programme is a joint effort of 29 European countries, runs from 2007 till 2011, and is managed by KNMI. OPERA-3 is designed to firmly establish the Programme as the host of the European Weather Radar Network.
10Weather Radars Operations Present and Future Frequency Band Needs Band selection is a function of the trade offs between range reflectivity and cost which vary as a function of the physics of rain attenuation.S-Band ( MHz) is well suited for detecting heavy rain at very long ranges. (Up to 300 km)C-Band ( MHz) represents a good compromise between range and reflectivity and cost and can provided rain detection up to a range of 200 kmX-Band ( MHz) weather radars are…More sensitive than S or C Band Radars Used for short range weather observations up to a range of 50 km
11Weather Radars Operations Data Utilization – Base Products Single PolarizationWeather Forecasting ProductsBase Reflectivity – Rainfall RateMean Radial Velocity - Wind information that related to wind motions within and relative to a storm Used for assessing rotation in a storm.Spectrum Width – Detecting turbulenceDual PolarizationDifferential Reflectivity - Indicator of drop shape.Correlation coefficient – Indicator of regions where the is a mixture of precipitations types.Specific Differential Phase – Also a good indicator of rain rateUsing the base data products, the processor produces higher-level derived data products for the radar user. This document will not address the derived data products in detail as the products vary from radar to radar and the numbers of products are quite large. To ensure accuracy of the derived data products, the base data products need to be accurately maintained.
12Weather Radars Operations Impact of Interference Corrupts Base ProductsLimits or nullifies the Radars Ability to….Detect wind speed and directionLocate and track hurricanes, typhoons, tornados, galesProvide reliable data to base severe storm or flash food warnings on.Decrease RangeBase Reflectivity – Distorts Rainfall Rate EstimatesTypes of InterferenceConstantTime VaryingPulsedWe continue to see interference despite trying to identify sources and mitigation strategies
13Weather Radars Operations Impact of Interference – Types of Interference (Constant) Meteo-04-9An example of impact of a constant interference on a radar precipitation mode can be seen in this figure. It is important to highlight that, although being a constant interference, the variation in impact is due to the rotation of the antenna [[more importantly side lobes and antenna pattern]], the maximum interference (in green on this picture) being produced in the azimuth of the interfering source. The narrow beam at 200 deg is likely a back lobe.
14Weather Radars Operations Impact of Interference – Types of Interference (Constant Interference from an RLAN)This figure shows the impact of interference from a Radio Local Area Network (RLAN )
15Weather Radars Operations Impact of Interference – Types of Interference (Pulsed) Interference freeInterference corruptedPulsed interference can have a significant impact on the reflectivity data that a meteorologist uses to forecast severe weather events. In some cases pulsed interference could result in a returned data that cannot reliably produce an image of targets in the atmosphere. An example of this can be seen in this figure.
16Weather Radars Operations Impact of Interference – Types of Interference (Wind Farms) [[Wind farms not listed on Slide 11 as a type of interference]]Thunderstorm characteristics could be masked or misinterpretedFalse reflectivity and radial velocity signatures could reduce forecaster's situational awareness during hazardous/severe weather eventsData masking or contamination over the wind farm and down range from the wind farm may negatively impact warning effectiveness.False precipitation estimates could negatively impact flash-flood warning effectivenessForecasters were able to ‘work around’ the impacts in this situation. Within ~18 km the impacts on data and operations begins to rapidly increase.Wind FarmThese farms are located between 20 miles and 35 miles directly southeast of the Weather Surveillance Doppler Radar located at the National Weather Service office in Cheektowaga (KBUF) in northern Erie county. The towers are on top of ridges at elevations that exceed 1600 feet above mean sea level. At this height, the rotating turbine blades of the wind farm impact the KBUF Doppler Radar beam. As you can see in the above image depicting most of western New York, the rotating wind turbines are having an affect on the radar beam. Wind turbine clutter or interference that shows up on the base reflectivity, velocity and spectrum width images produced by the Doppler radar can have several impacts including:Thunderstorm or winter storm characteristics could be masked or misinterpreted, reducing warning effectiveness in the vicinity of, and downrange of the wind farm.False signatures contaminating Doppler velocity data in the vicinity and downrange of the wind energy facility could reduce forecaster's situational awareness, particularly during hazardous/severe weather events. Data masking or contamination if thunderstorms develop over the wind farm may negatively impact warning effectiveness.False precipitation estimates could negatively impact flash-flood warning effectiveness. However, at the ranges of wind clutter shown here, NWS forecasters are able to “work around” the signatures and not cause an impact on forecast and severe weather operations.
17Weather Radars Operations Impact of Interference On Our Lives Routine weather forecastsSevere weather and flash flood warningsAviation and maritime safetyPersonal travel safetySafe, timely transport of personal and commercial goodsAgriculture – your source of foodPower managementHighway managementWater management
18Weather Radars Operations Impact of Interference At the end of the day, the bottom line is that interference dramatically reduces a Meteorologists ability to generate reliable forecasts…..
19Weather Radars Operations Impact of Interference – Protection Criteria Interference Protection Criteria: The highest interference level that does not degrade the system performance beyond performance requirements
20Weather Radars Operations Impact of Interference – Interference To Noise I/N Protection Criteria I/N is specified as a interference signal level relative to the radar noise floorInterference is added to receiver noise to produce a higher noise + interference levelHigher noise + interference level masks and corrupts weak but vital returnsThe current ITU-R protection criteria Level for Meteorological Radars is an I/N of -10 dB.
21ITU Definitions Weather Radars International Telecommunications Union (ITU) – U.N. organization responsible for international regulation of radio spectrum useInternational Radio Regulations – Treaty text maintained and enforced by the ITU that provides the regulations and table of frequency allocations for international radio spectrum useRadio Service - A type of radio operation, such as meteorological satellites, broadcasting, mobile-satelliteAllocation – The authority for a radio service to use a particular frequency bandLicense (or Assignment) – Authority for a particular radio station to use a specific frequency under the defined technical conditions and consistent with a frequency allocation
22ITU Definitions Applied To Meteorological Radars Meteorological Aids Service (MetAids) – 400MHz and 1680 MHz Bands RadiosondesIn the ITU, Meteorological Radars fall under the Radiodetermination ServiceITU Working Party 5B (WP 5B) is responsible for Meteorological Radars.Three allocations exist in the Radio Regulations specifically for meteorological radarsMHz- ground based radarsMHz- ground based radarsMHz- ground based and airborne radars
23Weather Radars Relevant ITU Documents Allocations In the band MHz, ground based radars used for meteorological purposes are authorized to operate on a basis of equality with stations of the aeronautical radionavigation service [[3000?]]Between 5600 and 5650 MHz, ground based radars used for meteorological purposes are authorized to operate on a basis of equality with stations of the maritime radionavigation serviceThe use of the band MHz by the aeronautical radionavigation service is limited to airborne weather radars and ground-based radars. … In the band MHz, ground-based radars used for meteorological purposes have priority over other radiolocation services
24Weather Radars Relevant ITU Documents Recommendation ITU-R M.1464-1 Content: Characteristics of meteorological radars and protection criteria for sharing studiesUse: Used for performing analysis between systems operating in the radiodetermination service operating in the frequency band MHz
25Weather Radars Relevant ITU Documents Recommendation ITU-R M.1849 Content: Technical and operational aspects of ground-based meteorological radarsUse: That the technical and operational aspects of meteorological radars as described in document be considered when conducting sharing studies and that the protection criteria for meteorological radars should be based upon Annex 1, in particular § 8.5, for assessing compatibility with interfering signal types from other services and applications.
26Weather Radars Relevant ITU Documents Report TU-R M.2136 Content: Interference protection criteria analysis and testing results in the MHz and MHz BandsUse: Reference document
27Weather Radars Relevant ITU Documents Report TU-R M.2136 Content: Interference protection criteria analysis and testing results in the MHz and MHz BandsUse: Reference document
28Weather Radars Relevant ITU Documents Handbook R-HDB-45-2008-MSW-E Content: Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and PredictionUse:“The Handbook provides comprehensive technical and operational information on current observation applications and systems and on the use of radio frequencies by meteorological systems, including meteorological satellites, radiosondes, weather radars, wind profiler radars and spaceborne remote sensing. It is intended for the meteorological (i.e. weather, water and climate) and radiocommunication communities, including governmental institutions, industry as well as the general public.”
29Looking Forward Future System Trends Weather Radar s Dual PolarizationPhased array antennasAllow other volume scan strategiesCan periodically return to an area of concern in atmosphere during a volume scanIncreased automationMode selectionSevere weather signature detectionThe deployment of X-band gap filler radars where short range (mitigating cone of silence) or high resolution performance is needed.Polarimetric radarThe next major upgrade is polarimetric radar, which adds vertical polarization to the current horizontal radar waves, in order to more accurately discern what is reflecting the signal. This so-called dual polarization allows the radar to distinguish between rain, hail and snow, something the horizontally polarized radars cannot accurately do. Early trials have shown that rain, ice pellets, snow, hail, birds, insects, and ground clutter all have different signatures with dual-polarization, which could mark a significant improvement in forecasting winter storms and severe thunderstorms. The deployment of the dual polarization capability (Build 12) and the contractor-installed hardware and software modifications to NEXRAD sites will begin in 2010 and last until 2012.Phased arrayBeyond dual-polarization, the advent of phased array radar will probably be the next major improvement in severe weather detection. Its ability to rapidly scan large areas would give an enormous advantage to radar meteorologists. Any large-scale installation by the NWS is unlikely to until sometime after Such a system would more likely be installed separate from the existing WSR-88D network, perhaps only in areas like the Great Plains where tornadoes are more common.
30Looking Forward Future ITU Activities Weather Radar s Updates to ITU-R Document ITU-R M.1464New ITU-R Report on Determining Maximum Interference Levels for Dual-Polarization Radars Operating in the MHz Band
31Conclusions Weather Radars Meteorological radars operate differently and produce different products than other radar typesThe differences need to be considered when conducting sharing studiesLimitations of physics dictate frequency band useMeteorological radars with higher sensitivity – lead to greater interference sensitivity
32Conclusions Weather Radars Meteorological Radars are the backbone of day to day local, regional, national and global weather forecastingUtilize segments of the Spectrum that are well suited to their operationProvide data for local severe storm, aviation and marine forecastingSave lives and injuries due to tornadoes – Simmons, K. M. and D. Sutter, 2005: WSR-88D Radar, Tornado Warnings and Tornado CasualtiesSensitive systems that must be protected from interference
33References Weather Radars Crum, T. D. and R. L. Alberty, 1993: The WSR-88D and the WSR-88D Operational Support Facility. Bull. Amer. Meteor. Soc., 74,Doviak, R.J. and Zrnic, D.S. Doppler Radar and Weather Observations. Dover Publications Inc, Mineola, NYSimmons, K. M. and D. Sutter, 2005: WSR-88D Radar, Tornado Warnings and Tornado Casualties. Weather Forecasting, 20,Burgess, D. W., T. Crum, and R. J. Vogt, 2008: Impacts of wind farms on WSR-88D Operations. Preprints, 24th Int. Conf. on Interactive Information Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, New Orleans, LA, Amer. Meteor. Soc., Paper 6B.3.Doppler Radar Meteorological Observations: Federal Meteorological Handbook No. 11, Parts A – D (contains general specifications and information on the NEXRAD radar) available at: http://www.roc.noaa.gov/FMH_11/default.asp.Isom, B. M. R. Palmer, G. Secrest, R. Rhoton, D. Saxion, J. Reed, T. Crum and R. Vogt, 2008: Wind Turbine Clutter Characterization and Mitigation on Federal Weather Radars (NEXRAD). Poster, American Wind Energy Association WINDPOWER 2008, Houston, TX.Isom, B. M., R. Palmer, G. Secrest, R. Rhoton, D. Saxion, J. Reed, T. Crum and R. Vogt, 2008: Detailed Observations of Wind Turbine Clutter With Scanning Weather Radars
34References Weather Radars Palmer, R., S. Torres, R. Zhang, 2008: Characterization, Detection, and Mitigating Wind Turbine Clutter on the WSR-88D Network. Briefing to the NEXRAD Technical Advisory Committee Meeting, Sept 2008, available at: VVogt, R. J., J. R. Reed, T. Crum, J. T. Snow, R. Palmer, B. Isom, and D. W. Burgess, 2007: Impacts of Wind Farms on WSR-88D Operations and Policy Considerations. Preprints, 23rd Int. Conf. on Interactive Information Processing Systems (IIPS) for Meteorology, Oceanography, and Hydrology, San Antonio, TX, Amer. Meteor. Soc., Paper 5B.7.Vogt, R. J., T. Crum, J. Reed, J. Sandifer, R. Palmer, B. Isom, J. Snow, D. Burgess and M. Paese, 2008: Weather Radars and Wind Farms – Working Together for Mutual Benefit. Poster, American Wind Energy Association WINDPOWER 2008, Houston, TX.Vogt, R. J., T. Crum, J. Reed, J. Sandifer, et.al.: A Way Forward Wind-Farm Weather Radar Coexistence, American Wind Energy Association Project Siting Workshop, February , 2009, Seattle, WATrisant, Philippe : Radio Frequency Threats on Meteorological Radars Operations, Proceedings of ERAD 2006, Fourth European Conference on Radar in Meteorology and Hydrology, September 18-22, 2006, Barcelona, SpainITU/WMO Handbook, Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and Prediction, 2008 Edition
35References Weather Radars ITU/WMO Handbook, Use of Radio Spectrum for Meteorology: Weather, Water and Climate Monitoring and Prediction, 2008 EditionReport ITU-R M.2136, Theoretical Analysis and Testing Results Pertaining to the Determination of Relevant Interference Protection Criteria of Ground-Based Meteorological radars, ITU 2008Report ITU-R M.2112, Compatibility/Sharing if Airport Surveillance and Meteorological Radar wit IMT Systems within the MHz Band, ITU 2007Recommendation ITU-R M , Characteristics of Radiolocation Radars, and Characteristics and Protection Criteria for Sharing Studies for Aeronautical Radionavigation and Meteorological Radars in the Radiodetermination Service Operating in the Frequency Band MHz, ITU 2003Recommendation ITU-R M.1849, Technical and Operation Aspects of Ground Based Meteorological Radars, ITU 2009