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64-404: The directional board is maneuverable, equipped with an X-band radar Mk.35 (later renamed AN/SPG-35 based on the naming convention for military electronic equipment) and an optical sight, and is manned with two operators on board. Target tracking by the operator's optical sight is also possible, but fully automated tracking is the basic operation, and blindfire is also possible for the first time in

128-403: A complete Canadian Doppler network between 1998 and 2004. France and other European countries had switched to Doppler networks by the early 2000s. Meanwhile, rapid advances in computer technology led to algorithms to detect signs of severe weather, and many applications for media outlets and researchers. After 2000, research on dual polarization technology moved into operational use, increasing

192-831: A more-or-less experimental basis, such as in the K band .) Notable deep space probe programs that have employed X band communications include the Viking Mars landers ; the Voyager missions to Jupiter , Saturn , and beyond; the Galileo Jupiter orbiter ; the New Horizons mission to Pluto and the Kuiper belt , the Curiosity rover and the Cassini-Huygens Saturn orbiter. An important use of

256-459: A rough outline of the Gulf of Mexico on a transparent sheet of plastic. During the broadcast, he held that transparent overlay over the computer's black-and-white radar display to give his audience a sense both of Carla's size and of the location of the storm's eye. This made Rather a national name and his report helped in the alerted population accepting the evacuation of an estimated 350,000 people by

320-529: A single coaxial cable with a power adapter connecting to an ordinary cable modem. The local oscillator is usually 9750 MHz, the same as for K u band satellite TV LNB. Two way applications such as broadband typically use a 350 MHz TX offset. Small portions of the X band are assigned by the International Telecommunication Union (ITU) exclusively for deep space telecommunications. The primary user of this allocation

384-496: A tornado devastated Union City, Oklahoma , just west of Oklahoma City . For the first time, a Dopplerized 10 cm wavelength radar from NSSL documented the entire life cycle of the tornado. The researchers discovered a mesoscale rotation in the cloud aloft before the tornado touched the ground – the tornadic vortex signature . NSSL's research helped convince the National Weather Service that Doppler radar

448-832: A verbal report increase with the severity of the returns. For example, the U.S. National NEXRAD radar sites use the following scale for different levels of reflectivity: Strong returns (red or magenta) may indicate not only heavy rain but also thunderstorms, hail, strong winds, or tornadoes, but they need to be interpreted carefully, for reasons described below. When describing weather radar returns, pilots, dispatchers, and air traffic controllers will typically refer to three return levels: Aircraft will try to avoid level 2 returns when possible, and will always avoid level 3 unless they are specially-designed research aircraft. Some displays provided by commercial television outlets (both local and national) and weather websites, like The Weather Channel and AccuWeather , show precipitation types during

512-464: Is a type of radar used to locate precipitation , calculate its motion, and estimate its type (rain, snow, hail etc.). Modern weather radars are mostly pulse-Doppler radars , capable of detecting the motion of rain droplets in addition to the intensity of the precipitation. Both types of data can be analyzed to determine the structure of storms and their potential to cause severe weather . During World War II, radar operators discovered that weather

576-401: Is called the radial Doppler velocity because it gives only the radial variation of distance versus time between the radar and the target. The real speed and direction of motion has to be extracted by the process described below. The phase between pulse pairs can vary from - π {\displaystyle \pi } and + π {\displaystyle \pi } , so

640-548: Is even incorporated into numerical weather prediction models to improve analyses and forecasts. During World War II, military radar operators noticed noise in returned echoes due to rain, snow, and sleet . After the war, military scientists returned to civilian life or continued in the Armed Forces and pursued their work in developing a use for those echoes. In the United States, David Atlas at first working for

704-566: Is not authorised to allocate frequency bands for military radio communication . This is also the case pertaining to X band military communications satellites . However, in order to meet military radio spectrum requirements, e.g. for fixed-satellite service and mobile-satellite service , the NATO nations negotiated the NATO Joint Civil/Military Frequency Agreement (NJFA). 2. 7250-7300 MHz

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768-475: Is often used in modern radars. The shorter wavelengths of the X ;band provide higher-resolution imagery from high-resolution imaging radars for target identification and discrimination. X-band weather radars offer significant potential for short-range observations, but the loss of signal strength ( attenuation ) under rainy conditions limits their use at longer range. X band 10.15 to 10.7 GHz segment

832-408: Is on the order of a millisecond , which is a thousand times longer than the pulse duration. The length of this phase is determined by the need for the microwave radiation (which travels at the speed of light ) to propagate from the detector to the weather target and back again, a distance which could be several hundred kilometers. The horizontal distance from station to target is calculated simply from

896-504: Is paired with 7975-8025 MHz for the MOBILE-SATELLlTE allocation. 3. The FIXED and MOBILE services are not to be implemented in the band 7250-7300 MHz in most NATO countries, including ITU Region 2. 4. In the band 7300-7750 MHz the transportable earth stations cannot claim protection from the other services. The Radio Regulations of the International Telecommunication Union allow amateur radio operations in

960-402: Is received power, P t {\displaystyle \scriptstyle P_{t}} is transmitted power, G {\displaystyle \scriptstyle G} is the gain of the transmitting/receiving antenna, λ {\displaystyle \scriptstyle \lambda } is radar wavelength, σ {\displaystyle \scriptstyle \sigma }

1024-765: Is the American NASA Deep Space Network (DSN). DSN facilities are in Goldstone, California (in the Mojave Desert ), near Canberra, Australia , and near Madrid, Spain , and provide continual communications from the Earth to almost any point in the Solar System independent of Earth rotation. (DSN stations are also capable of using the older and lower S band deep-space radio communications allocations, and some higher frequencies on

1088-413: Is the beam width (in radians). This formula assumes the beam is symmetrically circular, "r" is much greater than "h" so "r" taken at the beginning or at the end of the pulse is almost the same, and the shape of the volume is a cone frustum of depth "h". Between each pulse, the radar station serves as a receiver as it listens for return signals from particles in the air. The duration of the "listen" cycle

1152-480: Is the beam width in radians. In combining the two equations: Which leads to: The return varies inversely to R 2 {\displaystyle \,R^{2}} instead of R 4 {\displaystyle \,R^{4}} . In order to compare the data coming from different distances from the radar, one has to normalize them with this ratio. Return echoes from targets (" reflectivity ") are analyzed for their intensities to establish

1216-484: Is the designation for a band of frequencies in the microwave radio region of the electromagnetic spectrum . In some cases, such as in communication engineering , the frequency range of the X band is rather indefinitely set at approximately 7.0–11.2  GHz . In radar engineering, the frequency range is specified by the Institute of Electrical and Electronics Engineers (IEEE) as 8.0–12.0 GHz. The X band

1280-454: Is the radar cross section of the target and R {\displaystyle \scriptstyle R} is the distance from transmitter to target. In this case, the cross sections of all the targets must be summed: where c {\displaystyle \,c} is the light speed, τ {\displaystyle \,\tau } is temporal duration of a pulse and θ {\displaystyle \,\theta }

1344-948: Is the second harmonic of C-band and fourth harmonic of S-band . The European X-band frequency is used for the Compact Linear Collider (CLIC) . ELF 3 Hz/100 Mm 30 Hz/10 Mm SLF 30 Hz/10 Mm 300 Hz/1 Mm ULF 300 Hz/1 Mm 3 kHz/100 km VLF 3 kHz/100 km 30 kHz/10 km LF 30 kHz/10 km 300 kHz/1 km MF 300 kHz/1 km 3 MHz/100 m HF 3 MHz/100 m 30 MHz/10 m VHF 30 MHz/10 m 300 MHz/1 m UHF 300 MHz/1 m 3 GHz/100 mm SHF 3 GHz/100 mm 30 GHz/10 mm EHF 30 GHz/10 mm 300 GHz/1 mm THF 300 GHz/1 mm 3 THz/0.1 mm Weather radar Weather radar , also called weather surveillance radar ( WSR ) and Doppler weather radar ,

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1408-406: Is traversing is larger for areas farther away from the station, and smaller for nearby areas, decreasing resolution at farther distances. At the end of a 150 – 200 km sounding range, the volume of air scanned by a single pulse might be on the order of a cubic kilometer. This is called the pulse volume . The volume of air that a given pulse takes up at any point in time may be approximated by

1472-511: Is used for radar , satellite communication , and wireless computer networks . X band is used in radar applications, including continuous-wave , pulsed, single- polarization , dual-polarization, synthetic aperture radar , and phased arrays . X-band radar frequency sub-bands are used in civil , military , and government institutions for weather monitoring , air traffic control , maritime vessel traffic control , defense tracking , and vehicle speed detection for law enforcement. X band

1536-420: Is used for terrestrial broadband in many countries, such as Brazil, Mexico, Saudi Arabia, Denmark, Ukraine, Spain and Ireland. Alvarion , CBNL , CableFree and Ogier make systems for this, though each has a proprietary airlink. DOCSIS (Data Over Cable Service Interface Specification) the standard used for providing cable internet to customers, uses some X band frequencies. The home / Business CPE has

1600-400: Is used only for short-range units, and 1 cm Ka-band weather radar is used only for research on small-particle phenomena such as drizzle and fog. W band (3 mm) weather radar systems have seen limited university use, but due to quicker attenuation, most data are not operational. Radar pulses diverge as they move away from the radar station. Thus the volume of air that a radar pulse

1664-567: The Air Force and later for MIT , developed the first operational weather radars. In Canada, J.S. Marshall and R.H. Douglas formed the "Stormy Weather Group" in Montreal. Marshall and his doctoral student Walter Palmer are well known for their work on the drop size distribution in mid-latitude rain that led to understanding of the Z-R relation, which correlates a given radar reflectivity with

1728-665: The Engineering Research Center for Collaborative Adaptive Sensing of the Atmosphere (CASA), a multidisciplinary, multi-university collaboration of engineers, computer scientists, meteorologists, and sociologists to conduct fundamental research, develop enabling technology, and deploy prototype engineering systems designed to augment existing radar systems by sampling the generally undersampled lower troposphere with inexpensive, fast scanning, dual polarization, mechanically scanned and phased array radars. In 2023,

1792-487: The 1950s. Performance improvements continued after the war, and it became possible to start shooting in 2 seconds from the start of tracking for subsonic aircraft . Mk.68 GFCS was the standard for the Mark 42 5"/54 cal gun , but this machine was also used as a secondary directional board. Well known electric engineer Ivan A. Getting was involved in the creation of AN/SPG-35. The Japan Maritime Self-Defense Force requested

1856-420: The Earth is round, the radar beam in vacuum would rise according to the reverse curvature of the Earth. However, the atmosphere has a refractive index that diminishes with height, due to its diminishing density. This bends the radar beam slightly toward the ground and with a standard atmosphere this is equivalent to considering that the curvature of the beam is 4/3 the actual curvature of the Earth. Depending on

1920-479: The U.S. National Oceanic and Atmospheric Administration has been experimenting with phased-array radar as a replacement for conventional parabolic antenna to provide more time resolution in atmospheric sounding . This could be significant with severe thunderstorms, as their evolution can be better evaluated with more timely data. Also in 2003, the National Science Foundation established

1984-456: The US Navy. First, the target is captured by a spiral scan that slowly scans the space by swinging the beam at an angle of 6 degrees, and then a conical scan that quickly measures and distances by narrowing the beam swing angle to 0.5 degrees. Track the target by scanning. The speed of the tracking target is obtained by the gyroscope of the directional board and the tachometer generator of

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2048-518: The United States was in September 1961. As Hurricane Carla was approaching the state of Texas, local reporter Dan Rather , suspecting the hurricane was very large, took a trip to the U.S. Weather Bureau WSR-57 radar site in Galveston in order to get an idea of the size of the storm. He convinced the bureau staff to let him broadcast live from their office and asked a meteorologist to draw him

2112-466: The X band communications came with the two Viking program landers. When the planet Mars was passing near or behind the Sun, as seen from the Earth, a Viking lander would transmit two simultaneous continuous-wave carriers, one in the S band and one in the X band in the direction of the Earth, where they were picked up by DSN ground stations. By making simultaneous measurements at the two different frequencies,

2176-491: The amount of information available on precipitation type (e.g. rain vs. snow). "Dual polarization" means that microwave radiation which is polarized both horizontally and vertically (with respect to the ground) is emitted. Wide-scale deployment was done by the end of the decade or the beginning of the next in some countries such as the United States, France, and Canada. In April 2013, all United States National Weather Service NEXRADs were completely dual-polarized. Since 2003,

2240-469: The amount of time that elapses from the initiation of the pulse to the detection of the return signal. The time is converted into distance by multiplying by the speed of light in air: where c = 299,792.458 km/s is the speed of light , and n ≈ 1.0003 is the refractive index of air. If pulses are emitted too frequently, the returns from one pulse will be confused with the returns from previous pulses, resulting in incorrect distance calculations. Since

2304-499: The authorities, which was the largest evacuation in US history at that time. Just 46 people were killed thanks to the warning and it was estimated that the evacuation saved several thousand lives, as the smaller 1900 Galveston hurricane had killed an estimated 6000-12000 people. During the 1970s, radars began to be standardized and organized into networks. The first devices to capture radar images were developed. The number of scanned angles

2368-559: The distance tracking servo system . Ballistic calculation was performed by the Mk.42 ballistic computer housed in the ship, and it was possible to aim two types of guns at the same target by adding a ballistic calculation housing. During the war, there were many cases where radar tracking could not catch up with the attacking aircraft incoming at high speed. The first model of this model was delivered in August 1945, and has been in operation since

2432-448: The droplets or ice particles of interest, because Rayleigh scattering occurs at these frequencies. This means that part of the energy of each pulse will bounce off these small particles, back towards the radar station. Shorter wavelengths are useful for smaller particles, but the signal is more quickly attenuated. Thus 10 cm ( S-band ) radar is preferred but is more expensive than a 5 cm C-band system. 3 cm X-band radar

2496-418: The elevation angle of the antenna and other considerations, the following formula may be used to calculate the target's height above ground: where: A weather radar network uses a series of typical angles that are set according to its needs. After each scanning rotation, the antenna elevation is changed for the next sounding. This scenario will be repeated on many angles to scan the entire volume of air around

2560-670: The equipment of this model with the Harukaze-class destroyer , which was the first domestic escort ship after the war, but it was not approved by the US side, and the actual equipment was in the Second Defense Build-up Plan. In the United Kingdom , the MRS-3 (Medium Range System) was developed based on this model. The Type 903 radar tracker was commissioned in 1946 and 1958. The Type 904 radar tracker

2624-446: The formula v = h r 2 θ 2 {\displaystyle \,{v=hr^{2}\theta ^{2}}} , where v is the volume enclosed by the pulse, h is pulse width (in e.g. meters, calculated from the duration in seconds of the pulse times the speed of light), r is the distance from the radar that the pulse has already traveled (in e.g. meters), and θ {\displaystyle \,\theta }

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2688-769: The frequency range 10.000 to 10.500 GHz, and amateur satellite operations are allowed in the range 10.450 to 10.500 GHz. This is known as the 3-centimeter band by amateurs and the X-band by AMSAT . Motion detectors often use 10.525 GHz. 10.4 GHz is proposed for traffic light crossing detectors. Comreg in Ireland has allocated 10.450 GHz for Traffic Sensors as SRD. Many electron paramagnetic resonance (EPR) spectrometers operate near 9.8 GHz. Particle accelerators may be powered by X-band RF sources. The frequencies are then standardized at 11.9942 GHz (Europe) or 11.424 GHz (US), which

2752-485: The position and intensity of precipitation, were incorporated by weather services around the world. The early meteorologists had to watch a cathode-ray tube . In 1953 Donald Staggs, an electrical engineer working for the Illinois State Water Survey, made the first recorded radar observation of a " hook echo " associated with a tornadic thunderstorm. The first use of weather radar on television in

2816-504: The possibility to estimate the wind speed and direction where precipitation is present. A target's motion relative to the radar station causes a change in the reflected frequency of the radar pulse, due to the Doppler effect . With velocities of less than 70-metre/second for weather echos and radar wavelength of 10 cm, this amounts to a change only 0.1 ppm . This difference is too small to be noted by electronic instruments. However, as

2880-417: The precipitation rate in the scanned volume. The wavelengths used (1–10 cm) ensure that this return is proportional to the rate because they are within the validity of Rayleigh scattering which states that the targets must be much smaller than the wavelength of the scanning wave (by a factor of 10). Reflectivity perceived by the radar (Z e ) varies by the sixth power of the rain droplets' diameter (D),

2944-410: The private American company Tomorrow.io launched a Ka-band space-based radar for weather observation and forecasting. Weather radars send directional pulses of microwave radiation, on the order of one microsecond long, using a cavity magnetron or klystron tube connected by a waveguide to a parabolic antenna . The wavelengths of 1 – 10 cm are approximately ten times the diameter of

3008-407: The program does interpolations to produce an image with defined zones. These will include interpolation errors due to the calculation. Mesoscale variations of the precipitation zones will also be lost. More sophisticated programs use the numerical weather prediction output from models, such as NAM and WRF , for the precipitation types and apply it as a first guess to the radar echoes, then use

3072-577: The radar cannot "see" below the height above ground of the minimal angle (shown in green) or closer to the radar than the maximal one (shown as a red cone in the center). Because the targets are not unique in each volume, the radar equation has to be developed beyond the basic one. Assuming a monostatic radar where G t = A r ( o r G r ) = G {\displaystyle G_{t}=A_{r}(\mathrm {or} \,G_{r})=G} : where P r {\displaystyle \scriptstyle P_{r}}

3136-489: The radar within the maximum range. Usually, the scanning strategy is completed within 5 to 10 minutes to have data within 15 km above ground and 250 km distance of the radar. For instance in Canada, the 5 cm weather radars use angles ranging from 0.3 to 25 degrees. The accompanying image shows the volume scanned when multiple angles are used. Due to the Earth's curvature and change of index of refraction with height,

3200-399: The range from reflectivity at the expense of velocity range, or increasing the latter at the expense of range from reflectivity. In general, the useful range compromise is 100–150 km for reflectivity. This means for a wavelength of 5 cm (as shown in the diagram), an unambiguous velocity range of 12.5 to 18.75 metre/second is produced (for 150 km and 100 km, respectively). For

3264-577: The rate at which rainwater is falling. In the United Kingdom, research continued to study the radar echo patterns and weather elements such as stratiform rain and convective clouds , and experiments were done to evaluate the potential of different wavelengths from 1 to 10 centimeters. By 1950 the UK company EKCO was demonstrating its airborne 'cloud and collision warning search radar equipment'. Between 1950 and 1980, reflectivity radars, which measure

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3328-528: The relative velocity of the particles in the air. In the United States, the construction of a network consisting of 10 cm radars, called NEXRAD or WSR-88D (Weather Surveillance Radar 1988 Doppler), was started in 1988 following NSSL's research. In Canada, Environment Canada constructed the King City station, with a 5 cm research Doppler radar, by 1985; McGill University dopplerized its radar ( J. S. Marshall Radar Observatory ) in 1993. This led to

3392-480: The resulting data enabled theoretical physicists to verify the mathematical predictions of Albert Einstein 's General Theory of Relativity . These results are some of the best confirmations of the General Theory of Relativity. The new European double Mars Mission ExoMars will also use X band communication, on the instrument LaRa, to study the internal structure of Mars, and to make precise measurements of

3456-408: The rotation and orientation of Mars by monitoring two-way Doppler frequency shifts between the surface platform and Earth. It will also detect variations in angular momentum due to the redistribution of masses, such as the migration of ice from the polar caps to the atmosphere. The International Telecommunication Union (ITU), the international body which allocates radio frequencies for civilian use,

3520-408: The square of the dielectric constant (K) of the targets and the drop size distribution (e.g. N[D] of Marshall-Palmer ) of the drops. This gives a truncated Gamma function , of the form: Precipitation rate (R), on the other hand, is equal to the number of particles, their volume and their fall speed (v[D]) as: So Z e and R have similar functions that can be resolved by giving a relation between

3584-424: The surface data for final output. Until dual-polarization (section Polarization below) data are widely available, any precipitation types on radar images are only indirect information and must be taken with care. Precipitation is found in and below clouds. Light precipitation such as drops and flakes is subject to the air currents, and scanning radar can pick up the horizontal component of this motion, thus giving

3648-1553: The targets move slightly between each pulse, the returned wave has a noticeable phase difference or phase shift from pulse to pulse. Doppler weather radars use this phase difference (pulse pair difference) to calculate the precipitation's motion. The intensity of the successively returning pulse from the same scanned volume where targets have slightly moved is: I = I 0 sin ⁡ ( 4 π ( x 0 + v Δ t ) λ ) = I 0 sin ⁡ ( Θ 0 + Δ Θ ) { x = distance from radar to target λ = radar wavelength Δ t = time between two pulses {\displaystyle I=I_{0}\sin \left({\frac {4\pi (x_{0}+v\Delta t)}{\lambda }}\right)=I_{0}\sin \left(\Theta _{0}+\Delta \Theta \right)\quad {\begin{cases}x={\text{distance from radar to target}}\\\lambda ={\text{radar wavelength}}\\\Delta t={\text{time between two pulses}}\end{cases}}} So Δ Θ = 4 π v Δ t λ {\displaystyle \Delta \Theta ={\frac {4\pi v\Delta t}{\lambda }}} , v = target speed = λ Δ Θ 4 π Δ t {\displaystyle {\frac {\lambda \Delta \Theta }{4\pi \Delta t}}} . This speed

3712-434: The two of the form called Z-R relation : Where a and b depend on the type of precipitation (snow, rain, convective or stratiform ), which has different Λ {\displaystyle \Lambda } , K, N 0 and v. Radar returns are usually described by colour or level. The colours in a radar image normally range from blue or green for weak returns, to red or magenta for very strong returns. The numbers in

3776-460: The unambiguous Doppler velocity range is This is called the Nyquist velocity. This is inversely dependent on the time between successive pulses: the smaller the interval, the larger is the unambiguous velocity range. However, we know that the maximum range from reflectivity is directly proportional to Δ t {\displaystyle \Delta t} : The choice becomes increasing

3840-531: The winter months: rain, snow, mixed precipitations ( sleet and freezing rain ). This is not an analysis of the radar data itself but a post-treatment done with other data sources, the primary being surface reports ( METAR ). Over the area covered by radar echoes, a program assigns a precipitation type according to the surface temperature and dew point reported at the underlying weather stations . Precipitation types reported by human operated stations and certain automatic ones ( AWOS ) will have higher weight. Then

3904-477: Was a crucial forecasting tool. The Super Outbreak of tornadoes on 3–4 April 1974 and their devastating destruction might have helped to get funding for further developments. Between 1980 and 2000, weather radar networks became the norm in North America, Europe, Japan and other developed countries. Conventional radars were replaced by Doppler radars, which in addition to position and intensity could track

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3968-656: Was also developed as a derivative of the GWS.22 Seacat air defense missile system . In addition, the Mk.64 GUNAR, which changed the shooting command radar to the gun side equipment (initially the same AN/SPG-34 as the Mk.63 , later AN/SPG-48 ), was also developed, and this was mainly used by the Royal Canadian Navy . This later evolved into the Mk.69 , which was independently digitized and refurbished by Canada and changed its radar to SPG-515. X band The X band

4032-587: Was causing echoes on their screens, masking potential enemy targets. Techniques were developed to filter them, but scientists began to study the phenomenon. Soon after the war, surplus radars were used to detect precipitation. Since then, weather radar has evolved and is used by national weather services, research departments in universities, and in television stations ' weather departments. Raw images are routinely processed by specialized software to make short term forecasts of future positions and intensities of rain, snow, hail, and other weather phenomena. Radar output

4096-532: Was increased to get a three-dimensional view of the precipitation, so that horizontal cross-sections ( CAPPI ) and vertical cross-sections could be performed. Studies of the organization of thunderstorms were then possible for the Alberta Hail Project in Canada and National Severe Storms Laboratory (NSSL) in the US in particular. The NSSL, created in 1964, began experimentation on dual polarization signals and on Doppler effect uses. In May 1973,

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