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Doppler on Wheels
Fleet of truck-mounted weather radars From Wikipedia, the free encyclopedia
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Doppler on Wheels (DOW) is a fleet of quickly deployable truck-mounted weather radars managed by the FARM (Flexible Array of Radars and Mesonets) Facility, an American research company affiliated with the University of Alabama Huntsville.[1][2] The group, which started as the Center for Severe Weather Research, is led by atmospheric scientist Joshua Wurman, and is partially funded by the National Science Foundation, as part of the "Community Instruments and Facilities" program. The DOW fleet have been used throughout the United States since 1995, as well as occasionally in Europe and South America, to research hazardous and challenging weather phenomena such as tornados.[1] The name refers to the Doppler effect at the basis of modern weather radar technology.
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History
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The first DOW platform was created and deployed in 1995, substantially changing the design paradigm of targeted meteorological studies. Ground-breaking, extremely fine-scale data was collected in tornadoes[3] and hurricanes,[4] as well as other phenomena. DOWs, by virtue of providing especially fine-scale targeted observations, have been central to various scientific discoveries, "firsts", and pioneering observations, e.g. the first concrete documentation of specific impacts of weather modification cloud seeding, the first mapping of multiple-vortices in tornadoes, the quantification of tornado low-level wind structure, etc. The DOW program rapidly expanded and evolved to include the first mobile dual-Doppler weather radar network, the first mobile rapid-scan radar (the Rapid-Scan DOW, RSDOW),[1] and the first quickly-deployable 1-degree C-band radar, the C-band on Wheels (COW). The DOWs, Mobile Mesonets, PODs & POLEs, as well as many other devices were crucial for instrumentation in numerous field projects, including VORTEX, VORTEX2, COPS, MAP, ASCII, IHOP, SCMS, CASES, ROTATE, PAMREX, SNOWD-UNDER, FLATLAND, HERO, UIDOW, UNDEO[citation needed], LEE, PERILS,[5] WINTRE-MIX,[6] RELAMPAGO,[7] GRAINEX,[8] and others.
In late 2018, the DOW Facility debuted a new quickly-deployable C-band radar (or COW) featuring a larger antenna and 5 cm wavelength (as compared to the 3 cm wavelength of the DOWs). Due to the larger size of the antenna, the truck features a built-in crane allowing for the radar to be assembled on site. The COW was first deployed as part of the RELAMPAGO field campaign in Argentina in late 2018.[9]
The DOW fleet has collected data in 250 tornadoes and inside the cores of eighteen hurricanes. DOWs have been deployed to Europe twice,[10] for the MAP and COPS field programs, and to Alaska twice for the JAWS-Juneau projects, and to South America for RELAMPAGO. DOWs have operated as high as 12,700 feet (3,900 m) on Bristol Head and at 10,000 feet (3,000 m) for the ASCII project at Battle Pass.
The DOW fleet, PODS, and Mobile Mesonets have been featured on television, including Discovery Channel's series Storm Chasers (joined by the Tornado Intercept Vehicles and the Dominator SRV vehicles),[11] National Geographic Channel's specials Tornado Intercept and The True Face of Hurricanes, and PBS's Nova episode "The Hunt for the Supertwister," and others.[citation needed]
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Doppler on Wheels 1
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_During_Project_VORTEX_1995.jpg)
The Doppler on Wheels (DOW) radar program began in 1994 with the goal of fielding a mobile, but fully capable, pencil-beam, scanning, pulsed Doppler radar, with the real-time multiparameter displays, and versatile programmable volume scanning ability typical of stationary weather research systems.[12]
It was constructed from November 1994 to April 1995, in preparation for VORTEX-95. DOW 1 was able to deploy for the project, and able to observe several tornadoes. DOW 1 was also used for several other research projects, including Small Cumulus Mesoscale Study (SCMS) in Florida in 1995, the FLATLAND/LIFT Boundary Layer Experiment in Illinois in 1996, and a microburst study run by MIT/LL and the FAA in 1996. DOW 1 was decommissioned in 1997, with the creation of DOW 2 and DOW 3.[12]
_First_Mobile_Radar_Tornado_Velocity_and_Reflectivity_Scan_Hanston,_KS.jpg)
DOW 1 used the transmitter of a CP-2 radar provided by the National Center for Atmospheric Research, along with a surplus antenna, pedestal, and receiver hardware. It was mounted on a modified Chevrolet flatbed truck, costing roughly $50,000. In 1996, the radar was upgraded with the installation of a new 2.44 meter antenna, replacing the previous 1.88 meter antenna. The new antenna allowed for a decreased beamwidth of 0.93°, improving the radar's overall resolution.[12] This upgraded radar would later be used by DOW 3 upon its completion in 1997.
_Scan_of_Dimmitt,_TX_Tornado.jpg)
| Tx Power (Peak) | 40 kW |
| Antenna Dimension | 1.88 m Parabolic
(increased to 2.44 m in 1996) |
| Beamwidth (3 dB) | 1.22° in 1995
(decreased to 0.93° in 1996) |
| Pulsewidth (μs) | 0.5 - 2.0 μs |
| Pulselength (μs) | 0.5–1.0 μs in 1995
(decreased to 0.25–1 μs in 1996) |
| Gatelength | 70 – 300 m (0.5 - 2.0 μs)
(decreased to 25 – 300 m in 1996) |
| PRF | 500 – 2300 Hz w/stagger
(increased to 500 – 4,000 in 1996) |
| Polarization | V |
| Processing | PIRAQ-1 |
| Products | V, Z, NCP, SW, DCZ |
| Antenna Scan Speed | 0 - 30°s - 1 |
| Antenna Scan Modes | PPI, RHI, SUR |
VORTEX-95 Deployment
In an article published in the Fall/Winter 1995 NSSL Briefing newsletter, Project VORTEX director Erik Rasmussen discussed why the development of a mobile doppler radar was necessary after shortcomings faced during VORTEX-94 operations. While the mobile mesonets provided key insights into pressure, temperature, and humidity near the surface in the lead up to and during tornadogenesis, they failed to provide a detailed view of three dimensional airflow in the storm and its surrounding regions.[13] Without a detailed view of airflow and conditions above the surface, project VORTEX researchers were be unable to observe key ingredients and steps that occur during the formation of a tornado. While a NOAA WP-3 equipped with a C-Band doppler radar[14] and the National Center for Atmospheric Research's ELDORA aircraft equipped with a X-Band doppler radar[15] were used for VORTEX operations in both 1994 and 1995, they only provided data every 300 meters and were therefor unable to document the motion of air within small regions of the storm, especially the mesocyclone. This lack of information also meant that researchers were unable to verify several key hypothesis established prior to field operations.[13]
To obtain data on wind variation and movement from altitudes of 100 meters to 10,000 meters, VORTEX scientists and the NSSL collaborated with University of Oklahoma School of Meteorology Assistant Professor Dr. Joshua Wurman, who had spent the past several years developing doppler radar technology at the National Center for Atmospheric Research, to develop a truck mounted doppler radar in time for the VORTEX-95 field campaign.[13] The antenna pedestal and dish were taken from old military missile tracking radars, while the transmitter was provided by the NCAR from a CP-2 research radar. The receiver and signal processor were developed by Mitch Randell and Eric Loew, while the system was mostly built by NSSL technicians Paul Griffin and Dennis Nealson.[13] For their work on the Doppler on Wheels, Paul Griffin and Dennis Nealson were awarded the NOAA Bronze Medal.[16] Parts for the Doppler on Wheels were ordered in November and December 1994, with testing taking place during March and April 1995. DOW 1 was first deployed on May 12, and scanned its first tornado just 4 days later on May 16 near Hanston, Kansas. DOW 1 was deployed on a ridge to the south of town and scanned as the tornado progressed for 45 minutes.[13]
On June 2, DOW 1 was deployed to the Dimmitt Texas, where it would scan one of the most studied tornadoes in history. The chase initially started in Friona Texas, where DOW 1, along with the rest of VORTEX-95 intercepted a violent F4 tornado.[13] After dissipating, Erik Rasmussen directed DOW 1, driven by Jerry Straka and operated by Joshua Wurman, to drive south towards an intensifying mesocyclone near Dimmitt, Texas. DOW 1 deployed south of town, and was able to start scanning before the tornado touched down. This meant that for the first time, meteorologists were able to observe highly detailed reflectivity and velocity radar data throughout the entire tornadogenesis process.[13] After touching down, the tornado followed an arcing path, which kept it at a constant sub 2 miles from DOW 1. This close range radar intercept, combined with other data collected by probe teams, mobile mesonets, and airborne radar aircraft, resulted in the most comprehensive tornado research dataset ever produced, until VORTEX 2 intercepted the Goshen County, Wyoming EF2 in 2009.[17]
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Doppler on Wheels 2
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The second generation of DOWs were deployed in 1997, improving on virtually every aspect of the first. DOW 2 was built off the base of a modified 1995 Ford F700, being able to reach 74 mph and weighing 25,000 lbs when fully equipped with its radar and scientific instrumentation.[12]
DOW 2 used a surplus 2.44 m antenna from NCAR’s CP-2 radar, being able to achieve a beamwidth of 0.93°. This was mounted on a spare pedestal from NCAR's CP-3 radar, often noted for its bright red color. This pedestal came with improved scan rotation speed, now being able to achieve 60° per second.[12] The most important update was to the DOW's Tx power. While DOW 1 was only able to have a maximum transmit power of 40 kW, DOW 2 was able to reach a peak Tx power of 250 kW. This increase in power allowed for improved sensitivity to low reflectivity and clear air. The receiver was also redesigned to be compatible with mobile bistatic systems.[12]
_Participating_in_Intermountain_Precipitation_EXperiment_(IPEX)_2000.jpg)
| Tx Power (Peak) | 250 kW |
| Antenna Dimension | 2.44 m Parabolic |
| Beamwidth (3 dB) | 0.93° |
| Pulsewidth (μs) | 0.1 - 2.0 μs |
| Pulselength (μs) | 0.167 - 1.0 μs |
| Gatelength | 12.5 - 300 (0.08 - 2 μs) |
| PRF | 500–5000 Hz (+stagger) |
| Polarization | H or V |
| Processing | PIRAQ-2 |
| Products | V, Z, NCP, SW, DCZ |
| Antenna Scan Speed | 0 - 60°s - 1 |
| Antenna Scan Modes | PPI, RHI, SUR, Solar |
_Participating_in_Mesoscale_Alpine_Project_1999.jpg)
Research missions
DOW 2 was active from 1997 to 2007, first being used for Coastal Meteorology Research Program 1997 (CMRP) in Florida. While DOW 2 was used alongside DOW 3 for domestic research projects, including Radar Observations of Tornadoes And Thunderstorms Experiment (ROTATE) 1998-2004, and Hurricanes at Landfall (HAL), it is perhaps more notable for the research it conducted in Europe. DOW 2 was deployed to Switzerland in 1999 for the Mesoscale Alpine Programme (MAP), studying atmospheric and hydrological processes over mountainous terrain with the goal of better understanding how complex topography impacts weather systems.[19] In 2007, DOW 2 was deployed to France and Germany for the Convective and Orographically Induced Precipitation Study (COPS), studying how orographic terrain influences convective precipitation. According to the U.S. Department of Energy’s Atmospheric Radiation Measurement (ARM), there were three primary questions investigated:[20]
- What are the processes responsible for the formation and evolution of convective clouds in orographic terrain?
- What are the microphysical properties of orographically induced clouds and how do these depend on dynamics, thermodynamics, and aerosol microphysics?
- How can convective clouds in orographic terrain be represented in atmospheric models based on AMF, COPS, and GOP data?
After COPS 2007, DOW 2 was retired with the introduction of DOW 6 at the start of the 2008 storm season.[21]
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Doppler on Wheels 3
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_Participating_in_Intermountain_Precipitation_EXperiment_(IPEX)_2000.jpg)
_Participating_in_Intermountain_Precipitation_EXperiment_(IPEX)_2000_2.jpg)
DOW 3 was the other second generation Doppler on Wheels developed in 1997, being finished shortly after DOW 2 and replacing the now retired DOW 1. DOW 3 was largely the same as DOW 2, but incorporated several pieces of hardware including the green radar pedestal and a differently shaped radar dish that were originally used on DOW 1. The actual truck, a modified 1995 Ford F700, was identical to DOW 2 apart from small cosmetic differences.[12] Both second generation DOWs were also outfitted with an extendable 10 meter meteorological and communication masts, allowing for both atmospheric measurements such as temperature, wind speed, and pressure, while also allowing for extended radio communications and better internet signal.
DOW 3’s radar specifications were also the same as DOW 2, excluding the cosmetic radar dish covering the antenna. This included a peak Tx power of 250 kW, a 2.44 m parabolic antenna, a beamwidth of 0.93°, a pulsewidth of 0.1 - 2.0 μs, and a staggered PRF between 500–5000 Hz. In 1999, DOWs 2 and 3 were upgraded with new antenna control hardware and software.[12]
| Tx Power (Peak) | 250 kW |
| Antenna Dimension | 2.44 m Parabolic |
| Beamwidth (3 dB) | 0.93° |
| Pulsewidth (μs) | 0.1 - 2.0 μs |
| Pulselength (μs) | 0.167 - 1.0 μs |
| Gatelength | 12.5 - 300 (0.08 - 2 μs) |
| PRF | 500–5000 Hz (+stagger) |
| Polarization | H or V |
| Processing | PIRAQ-2 |
| Products | V, Z, NCP, SW, DCZ |
| Antenna Scan Speed | 0 - 60°s - 1 |
| Antenna Scan Modes | PPI, RHI, SUR, Solar |
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Doppler on Wheels 4 (Dual Polarization)
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DOW 4 was ordered by the National Observatory of Athens and completed in 2000, first participating in precipitation studies at the University of Iowa. Unlike DOWs 1, 2, and 3, it was not part of the University of Oklahoma Mobile Radar Research Lab and therefor constructed as a joint venture by the National Center for Atmospheric Research and Wurman's private company, BINET Inc.[12] It was built on a 1999 Chevrolet 3500HD chassis, smaller than the Ford F700 used for DOWs 2 and 3 but better optimized for narrower European roadways.[12]
DOW 4 was first Doppler on Wheels to possess dual polarization,[12] meaning it could scan using horizontal and vertical radar beams simultaneously and therefor better differentiate between different types of precipitation.[23] Before being transferred to the National Observatory of Athens and stationed at the Penteli Observatory, DOW 4 was able to participate in several research studies including ROTATE-2001,[12] CAMEX-4 Keys Area Microphysics Project (KAMP),[24] and The International H2O Project 2002 (IHOP).[18]
| Tx Power (Peak) | 50 kW |
| Antenna Dimension | 2.44 m Parabolic |
| Beamwidth (3 dB) | 0.93° |
| Pulsewidth (μs) | 0.1 - 2.0 μs |
| Gatelength | 30 - 300 (0.2 - 2 μs) |
| PRF | 500–7000 Hz (+stagger) |
| Polarization | H and V simultaneous |
| Processing | BINET Board |
| Products | V, Z, SW, NCP, DCZ, ZDR, ρHV |
| Antenna Scan Speed | 0 - 60°s - 1 |
| Antenna Scan Modes | PPI, RHI, SUR, Solar |
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Doppler on Wheels 6
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Doppler on Wheels 6 (DOW 6) was introduced in 2008 to replace the two 2nd Generation Doppler on Wheels units (DOWs 2 and 3) in preparation for the VORTEX 2 research project in 2009 and 2010. DOW 6, along with DOWs 7 and 8, were built on 7500 series International Workstar Trucks, which are more powerful and rugged than the Ford F700 used for DOWs 2 and 3 or the 4300/4700 Workstar series used for other mobile radars including NOXP, MAX, and Smart-R. Mounted on the 7500 series, DOW 6 was able to reach peak speeds of 75 mph and boasted increased acceleration, allowing for faster deployment times.[25]
After 17 years of successful deployments, DOW 6 was retired in 2025, having produced one of the most comprehensive mobile radar datasets in severe weather research history. DOW 6 was subsequently replaced by the next generation of Doppler on Wheels radar trucks, dubbed "DOW A" and "DOW B".
_2009_VORTEX_2.jpg)
| Tx Power (Peak) | 2x 250 kW |
| Antenna Dimension | 2.44 m Parabolic |
| Beamwidth (3 dB) | 0.93° |
| Pulsewidth(μs) | 0.167 - 1.0 μs |
| Gatelength (m) | 12.5 – 600 m |
| PRF | 500 – 6000 Hz (+stagger) |
| Polarization | Dual-Frequency Dual-Polarization |
| Processing | TITAN |
| Products | LDR, ZDR. ρHV, V, Z, SW, NCP, IQ |
| Antenna Scan Speed | 50 deg/s−1 |
| Antenna Scan Modes | PPI, RHI, SUR, Solar |
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Doppler on Wheels 7
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.jpg)
Doppler on Wheels 7 (DOW 7) was introduced one year after DOW 6, in time for the start of the 2009 storm season and VORTEX 2 research project. Like DOW 6, it was built on a 7500 series International Workstar Truck and featured comparable radar and processing specifications. These differences were primarily present in 2009, where DOW 7 utilized a slightly lower pulselength of 150 - 2000 ns compared to DOW 6's 200 - 2000 ns pulselength.[27] There were also some slight differences in the cabin design and layout, but these are negligible and had no impact on the radar's performance.
DOW 7 was retired at the end of 2024 to make way for the next generation of Doppler on Wheels radar trucks. These two new DOWs, named "DOW A" and "DOW B", made several improvements on DOWs 6 and 7 by improving ergonomics, field maintenance, reduced front-sector radar beam blockage, new computers, new transmitters, new antenna control, identical layouts, and new trucks.[28]
_2009_VORTEX_2_Mast_Extended.jpg)
| Tx Power (Peak) | 2x 250 kW |
| Antenna Dimension | 2.44 m Parabolic |
| Beamwidth (3 dB) | 0.93° |
| Pulsewidth(μs) | 0.167 - 1.0 μs |
| Gatelength (m) | 12.5 – 600 m |
| PRF | 500 – 6000 Hz (+stagger) |
| Polarization | Dual-Frequency Dual-Polarization |
| Processing | TITAN |
| Products | LDR, ZDR. ρHV, V, Z, SW, NCP, IQ |
| Antenna Scan Speed | 50 deg/s−1 |
| Antenna Scan Modes | PPI, RHI, SUR, Solar |
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Capabilities
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As of May 2024, the current operational Doppler on Wheels vehicles include the CROW (which consists of the DOW8/RSDOW/Mini-COW)[29], and the COW (C-band On Wheels, occasionally referred to as the COW1).
The COW consists of a C-band dual-polarization dual-frequency radar system utilizing two 1 MW transmitters set to a 5 cm wavelength configuration.[30] The CROW consists of three separate configurations, the DOW8, which utilizes a single-polarization 250 kW X-band transmitter, the RSDOW, which consists of a 7-second rapid-scan passive phased array antenna, utilizing a TWT 40 kW X-band transmitter system,[31] and the Mini-COW, utilizing a singular 1 MW C-band transmitter capable of 50-second dual-polarization updates.[29]
As of May 2024, the DOW6 and DOW7 are currently undergoing overhauls with new equipment, including the vehicles themselves, the transmitters, and the computing systems, as well as the integration with the new GURU software.[29] The previous iterations of the DOW6 and DOW7 utilized dual-polarization dual-frequency 250 KW X-band transmitters, and were the most powerful mobile X-band systems at the time.
On 27 April 2025, @DOWFacility on X (formerly Twitter) posted "DOW6’s last day. At over 17 years old (that’s 170 in radar years!), DOW6 has joined DOWs 1,2, and 3 in radar heaven. DOW6 was the longest lived DOW. Its first research mission was for ROTATE in 2008 and its last research mission was Hurricane Milton in 2024.". DOW 6 has since been retired, and DOW A is its successor.
DOWs are frequently deployed with the tightly integrated surface instrumentation network of the FARM.[30] Several instrumented mobile mesonet pickup trucks host in situ weather instrumentation on 3.5-metre (11 ft) masts to complement the remote sensing radars. These mobile mesonets also carry approximately twenty instrumented "PODS", which are ruggedized quickly deployable weather stations designed to survive inside tornadoes, tropical cyclones, and other adverse environments, and a Polenet comprising instrumentation deployed on poles, railings, fences, etc. during hurricane landfalls. An array of up to seven upper air and swarm sounding systems can also be deployed with the DOWs. The DOW fleet is sometimes accompanied by a Mobile Operations and Repair Center (MORC), a large van containing workstations for in-field coordination, data management, and equipment repair.[32]
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Findings
DOW data led to the discovery of sub-kilometer hurricane boundary layer rolls, which likely modulate wind damage and may play a key role in hurricane intensification. DOW data revealed some of the most intense tornadic winds ever recorded (the Bridge Creek–Moore tornado, 3 May 1999, the El Reno tornado, 31 May 2013, and the Greenfield, Iowa Tornado, 21 May 2024),[33][34] and the largest tornadic circulation ever documented (the Cimarron City–Mulhall–Perry Tornado, which also occurred on 3 May 1999),[35] and made the first 3D maps of tornado winds and sub-tornadic vortex winds, and documented intense vortices within lake-effect snow bands. About 70 peer-reviewed scientific publications have used DOW data.[citation needed]
DOW data has led to the discovery of the descending reflectivity core, a microscale phenomenon that may aid in tornadogenesis.
Future instrumentation
There are currently two major projects planned to expand the FARM's capabilities. The first is the creation of an S-band on Wheels Network (SOWNET) featuring four quickly-deployable S-band radars with 10 cm wavelengths capable of seeing through intense precipitation. These smaller truck-mounted radars would replace a single large S-band radar, allowing for dual-Doppler analyses and quicker deployment times. The second planned project is the Bistatic Adaptable Radar Network (BARN) which will be integrated with existing DOWs and the COW to provide high resolution wind vector observations without the need for multiple, expensive transmitters. These bistatic receivers will consist of small antennas that can be deployed like Pods or mounted onto a Mobile Mesonet or similar vehicle.[36]
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Gallery
FARM logo white
Probes, Scout, and DOW at PECAN 2015
DOW 7 at PECAN 2015
DOW 5
C-Band on Wheels at FARM Facility
C-Band on Wheels
C-Band on Wheels Radar
C-Band on Wheels Generator
_PECAN_2015_Media_Day.jpg)
_Rapid_Scan_with_Tornado_2003.jpg)
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_at_FARM_Facility_5.jpg)
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See also
References
External links
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