Doppler on Wheels

Flexible Array of Radars and Mesonets Facility

Abbreviation	FARM
Formation	2003 (2003)
Founders	Joshua Wurman
Type	Research facility
Focus	Severe weather research
Headquarters	Boulder, Colorado, United States
Location	Boulder, Colorado, United States
Region served	United States
Fields	Meteorology and Radar Development
Executive Director	Joshua Wurman
Managing Director	Karen Kosiba
Affiliations	University of Alabama in Huntsville Severe Weather Institute - Radar & Lightning Laboratory
Website	www.farmfacility.org//
Formerly called	University of Oklahoma Mobile Radar Research Lab (1995-2002), Center for Severe Weather Research (CSWR) (2003-2020)

Doppler on Wheels 8, Scout vehicles, and probes during PECAN 2015 media day.

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. 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. The name refers to the Doppler effect at the basis of modern weather radar technology.

Data gathered by a Doppler on Wheels unit showing a tornado near La Grange, Wyoming

History

See also: Mobile radar observation of tornadoes

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 and hurricanes, 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), 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, LEE, PERILS, WINTRE-MIX, RELAMPAGO, GRAINEX, 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.

The DOW fleet has collected data in 250 tornadoes and inside the cores of eighteen hurricanes. DOWs have been deployed to Europe twice, 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), 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.

Doppler on Wheels 1

DOW 1

Country of origin	USA
Designer	Joshua Wurman
Introduced	1994
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 2300 Hz
Beamwidth	(3dB) 1.22° in 1995, decreased to 0.93° in 1996
Pulsewidth	0.5 - 2.0 μs
Power	40 kW (Peak Tx Power)
Other names	Project Vortex - Mobile Radar No.1

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.

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.

Velocity and Reflectivity scan of Hanston, KS tornado on May 16th, 1995. This is the first truck mounted mobile weather radar scan of a tornado in history.

NSSL Project Vortex - Mobile Radar No.1 SE of Shamrock, Texas

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. This upgraded radar would later be used by DOW 3 upon its completion in 1997.

Dimmitt, Texas Tornado on June 2nd, 1995

DOW 1 scan of Dimmitt, Texas tornado taken at 7:06 PM CDT on June 2nd, 1995

DOW 1 Radar Specifications

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. 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 and the National Center for Atmospheric Research's ELDORA aircraft equipped with a X-Band doppler radar 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.

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. 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. For their work on the Doppler on Wheels, Paul Griffin and Dennis Nealson were awarded the NOAA Bronze Medal. 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.

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. 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. 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.

DOW 1 Research Missions

Year	Name	Full Name	Location	Focus
1995	VORTEX	Verification of the Origins of Rotation in Tornadoes Experiment	Great Plains	Tornadoes
1995	SCMS	Small Cumulus Mesoscale Study	Florida	Cloud convection measurement
1996	FLATLAND	FLATLAND/LIFT	Illinois	Boundary layer
1996	Microburst	MIT Microburst	New Mexico	Microbursts
1996	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall

Doppler on Wheels 2

DOW 2

Country of origin	USA
Designer	Joshua Wurman
Introduced	1997
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 5000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.1 - 2.0 μs
Power	250 kW (Peak Tx Power)
Other names	2nd Generation Doppler on Wheels

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.

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. 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.

Doppler on Wheels 2 (DOW 2) during IPEX 2000, taken sometime between 31 January - 25 February 2000.

DOW 2 Radar Specifications

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

Doppler on Wheels 2 (DOW 2) Participating in Mesoscale Alpine Project 1999 (MAP) Near Lodrino, Switzerland

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. 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:

• 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.

DOW 2 Research Missions

Year	Name	Full Name	Location	Focus
1997-98	CMRP	Coastal Meteorology Research Program	Florida	Marine boundary layer
1997-2004	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall
1998	ROTATE-98	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
1998	CALJET	California Landfall Jet Experiment	California	Coastal low-level jets, El Nino
1999	ROTATE-99	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
1999	MAP	Mesoscale Alpine Programme	Switzerland	Orographic precipitation
1999-2002	JAWS	Juneau Airport Wind Systems	Juneau, Alaska	Mountain turbulence
2000	IPEX	Intermountain Precipitation Experiment	Utah	Orographic precipitation
2000	ROTATE-2000	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2000	STEPS	Severe Thunderstorm Electrification and Precip Study	Colorado–Kansas	Thunderstorm electrification
2000–01	GCW	Goodwin Creek Watershed	Mississippi	Hydrology
2001	ROTATE-2001	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2002	IHOP	International H2O Project	Great Plains	Convection initiation
2002	Hayman Fire	Hayman Fire	Colorado	Fire
2003	ROTATE-2003	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2003	CRP	Canadian River Project	Oklahoma	Bacteria/chemical agent
2004	ROTATE-2004	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2007	COPS	Convective and Orographically induced Precip Study	Germany–France	Convective and orographic precipitation

Doppler on Wheels 3

DOW 3

Country of origin	USA
Designer	Joshua Wurman
Introduced	1997
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 5000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.1 - 2.0 μs
Power	250 kW (Peak Tx Power)
Other names	2nd Generation Doppler on Wheels

Doppler on Wheels 3 during Intermountain Precipitation EXperiment (IPEX) operations

Doppler on Wheels 3 radar

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. 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.

DOW 3 Radar Specifications

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

DOW 3 Research Missions

Year	Name	Full Name	Location	Focus
1997-98	CMRP	Coastal Meteorology Research Program	Florida	Marine boundary layer
1997-2007	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall
1998	ROTATE-98	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
1998	CALJET	California Landfall Jet Experiment	California	Coastal low-level jets, El Nino
1999	ROTATE-99	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
1999-2002	JAWS	Juneau Airport Wind Systems	Juneau, Alaska	Mountain turbulence
2000	IPEX	Intermountain Precipitation Experiment	Utah	Orographic precipitation
2000	ROTATE-2000	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2000	STEPS	Severe Thunderstorm Electrification and Precip Study	Colorado–Kansas	Thunderstorm electrification
2001	ROTATE-2001	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2002	IHOP	International H2O Project	Great Plains	Convection initiation
2002	Prince Albert	Prince Albert Fire	Saskatchewan	Fire
2003	ROTATE-2003	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2003	Chico	Chico Fire Suppression	California	Fire suppression guidance
2003	CRP	Canadian River Project	Oklahoma	Bacteria/chemical agent
2004	ROTATE-2004	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2005	ROTATE-2005	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Low level tornado radar scans and TIV guidance
2006	ROTATE-2006	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Low level tornado radar scans and TIV guidance
2007	ROTATE-2007	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Low level tornado radar scans and TIV guidance
2007	COPS	Convective and Orographically induced Precip Study	Germany–France	Convective and orographic precipitation

Doppler on Wheels 4 (Dual Polarization)

DOW 4

Country of origin	USA
Manufacturer	BINET Inc and National Center for Atmospheric Research
Designer	Joshua Wurman
Introduced	2000
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 7000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.1 - 2.0 μs
Power	50 kW (Peak Tx Power)
Other names	XPOW, XPOL, Dual Polarization Doppler on Wheels, X-band Polarimetric On Wheels

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. 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.

DOW 4 was first Doppler on Wheels to possess dual polarization, meaning it could scan using horizontal and vertical radar beams simultaneously and therefor better differentiate between different types of precipitation. 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, CAMEX-4 Keys Area Microphysics Project (KAMP), and The International H2O Project 2002 (IHOP).

Penteli Observatory where DOW4 is stationed

DOW 4 Radar Specifications

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

DOW 4 Research Missions

Year	Name	Full Name	Location	Focus
2000-2001	Iowa	University of Iowa Precipitation Experiments	Iowa	Precipitation
2001	ROTATE-2001	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2001	CAMEX-4 KAMP	Convection and Moisture Experiment 4 Keys Area Microphysics Project	Florida	Tropical Cyclones and quantitative precipitation estimates improvement
2002	IHOP	International H2O Project	Great Plains	Convection initiation
Present	Greece	National Observatory of Athens Radar	Greece	Radar observation

Doppler on Wheels 5 (Rapid Scan)

DOW 5

Country of origin	USA
Designer	Joshua Wurman
Introduced	2003
No. built	1
Type	Weather Radar
Frequency	9.3-9.8 GHz (X-band)
PRF	500 - 7000 Hz (+stagger)
Beamwidth	(3dB) 0.8°
Pulsewidth	0.125 - 2.0 μs
Power	40 kW (Peak Tx Power)
Other names	RS DOW, Rapid Scan DOW

DOW 5 radar loop of 2009 Goshen County tornado during VORTEX 2 operations.

DOW 5 back profile.

DOW 5 during VORTEX 2.

DOW 5 began construction in 2001 with the goal of fitting a phased array radar capable of rapidly scanning a storm environment and detecting small changes in storm evolution that occur within timescales too short to detect using traditional parabolic antenna radars, including those on DOWs and National Weather Service WSR-88D NEXRAD radars. While originally planned to be part of the University of Oklahoma's Mobile Radar Research Lab, DOW 5 was completed in 2003 and transferred to the Center for Severe Weather Research, along with Wurman's other DOW radars.

DOW 5 is unique in that it was the first mobile weather radar platform to feature a phased array radar, which utilizes many smaller antennas to near simultaneously transmit and receive high resolution data in very short timescales usually missed by slower scanning mechanical radars. Because conventional phased array technologies are prohibitively expensive to design and deploy, especially in the early 2000s when DOW 5 was developed, it utilizes a hybrid electronic and mechanical scanning system. DOW 5 maintains mechanically rotating azimuth while incorporating frequency based electronic vertical steering. This is achieved by using a vertically aligned array of slotted waveguide antennas that produce 6 - 10 near simultaneous radar beams at different frequencies, providing a single polarization volumetric scan at 6 elevations in 6 seconds. DOW 5's radar does have several drawbacks compared to parabolic antenna radars, primarily considering its range. DOW 5 has a radar scanning range of 10 km, although ideal measurements are much closer at sub 3 km ranges. This is much shorter than other DOWs, which have a maximum radar range of 60 km. This makes DOW 5's general application much more narrow, especially on research missions where there is greater uncertainty and sparse road networks.

DOW 5 Radar Specifications

Tx Power (Peak)	40 kW
Phased Array Dimension	2.4 m x 2.6 - 3.0 m
Phased Array Technology Type	Frequency-based, electronic steering
Frequency Range	9.3 - 9.8 GHz
Beamwidth (3 dB)	0.8° (6 beams)
Pulsewidth (μs)	0.125 - 2.0 μs
Gatelength	25 - 75 m (0.2 - 2 μs)
PRF	500-7000 Hz (+stagger)
Polarization	H or V
Processing	PIRAQ-3
Products	V, Z, SW, NCP, P
Antenna Scan Speed	0 - 50°s - 1 (7 second volumes)
Antenna Scan Modes	PPI, RHI, SUR, Solar

Meteorological Application of Rapid-Scan Technology

Rapid scanning radars are incredibly useful for studying tornadoes, microbursts, hurricanes, hurricane boundary layer wind streaks, and other meteorological phenomenon that occur within incredibly short timescales. In the case of tornadoes, rapid scan radar data is crucial to understand they key processes in the lead up to and during tornadogenesis, what tornadogenesis mode is occurring (non-descending, descending, or simultaneous), what changes in a storm can lead to the sudden strengthening or weakening of a tornado, what processes precede and occur during tornado dissipation, and how factors such as RFD play a role throughout a tornado's lifespan. For hurricanes, rapid scanning technology allows for radars to observe and study vortex Rossby waves, tornado-scale vortices within hurricanes that last less than 10 seconds, hurricane boundary layer rolls, and provide an overall better understanding of destructive winds within hurricanes.

DOW 5 Research Missions

Year	Name	Full Name	Location	Focus
2003	ROTATE-2003	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2003-2011	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall
2004	ROTATE-2004	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans
2005	ROTATE-2005	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Low level tornado radar scans and TIV guidance
2009-2010	VORTEX 2	Verification of the Origins of Rotation in Tornadoes Experiment 2	Great Plains	Tornadoes

Doppler on Wheels 6

DOW 6

Country of origin	USA
Designer	Joshua Wurman
Introduced	2008
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.167 – 1.0 μs
RPM	50 deg/s-1
Diameter	2.44 m
Power	2x 250 kW (Peak Tx Power)

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.

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".

Doppler on Wheels 6 during 2009 VORTEX 2 operations.

DOW 6 Radar Specifications

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 (H or V before being upgraded in 2010)
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

DOW 6 Research Missions

Year	Name	Full Name	Location	Focus
2008	ROTATE-2008	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2008-2024	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall
2009-2010	VORTEX 2	Verification of the Origins of Rotation in Tornadoes Experiment 2	Great Plains	Tornadoes
2011	ROTATE-2011	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2012	ROTATE-2012	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	ROTATE-2013	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	OWLeS	Ontario Winter Lake-effect Systems	New York	Lake effect storms
2013	Bristol Head	Bristol Head Fire	Colorado	Fire-scar flooding
2014	ROTATE-2014	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2015	Cape Cod	Cape Cod Snowpocalypse	Cape Cod	Snowbands
2015	PECAN	Plains Elevated Convection at Night	Great Plains	Nocturnal MCS
2015-2016	OLYMPEX	Olympic Mountain Experiment	Olympics	Orographic precipitation
2015-2016	MASCRAD	Multiple Angle Snow Camera-Radar Experiment	Colorado	Snowflake morphology
2016	TWIRL 2016	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2017	SNOWIE	Seeded Natural Orographic Wintertime Clouds: Idaho Experiment	Idaho	Orographic cloud seeding
2017	TWIRL 2017	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2017	Eclipse	Eclipse	Wyoming	Solar eclipse effect on BL
2018	TWIRL 2018	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2018	GRAINEX	The Great Plains Irrigation Experiment	Nebraska	Effect of irrigation on BL
2018	RELAMPAGO	Remote Sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations	Argentina	Severe convection in Argentina
2019	TWIRL 2019	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2021	TWIRL 2021	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2022	WINTRE-MIX	Winter Precipitation Type Research Multi-scale Experiment	Northern New York and Southern Quebec	Project to study mixed precipitation in near-freezing environments and the multi-scale processes that influence precipitation type.
2022-2023	PERiLS	Propagation, Evolution and Rotation in Linear Storms	Southeast	QLCS Tornadoes
2024	BEST	Boundary-layer Evolution and Structure of Tornadoes	Great Plains	Tornadoes and boundary layer.

Doppler on Wheels 7

DOW 7

Country of origin	USA
Designer	Joshua Wurman
Introduced	2009
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.167 – 1.0 μs
RPM	50 deg/s-1
Diameter	2.44 m
Power	2x 250 kW (Peak Tx Power)

DOW 7 reflectivity during VORTEX 2 Goshen County, WY tornado on June 5th, 2009.

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. 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.

Doppler on Wheels 7 during 2009 VORTEX 2 Operations

DOW 7 Radar Specifications

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 (H or V before being upgraded in 2010)
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

DOW 7 Research Missions

Year	Name	Full Name	Location	Focus
2008	ROTATE-2008	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2008-2024	HAL	Hurricanes at Landfall	Gulf/Atlantic Coast	Hurricanes at landfall
2009-2010	VORTEX 2	Verification of the Origins of Rotation in Tornadoes Experiment 2	Great Plains	Tornadoes
2010-2011	LLAP	Long Lake Axis-Parallel lake effect storms	New York	Lake effect storms
2010-2011	ASCII	AgI Seeding of Clouds Impact Investigation	Wyoming	Orographic cloud seeding
2011	ROTATE-2011	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2012	ROTATE-2012	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	ROTATE-2013	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	OWLeS	Ontario Winter Lake-effect Systems	New York	Lake effect storms
2013-2014	Pawnee	Pawnee Grasslands	Colorado	Boundary layer
2014	ROTATE-2014	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2015	Cape Cod	Cape Cod Snowpocalypse	Cape Cod	Snowbands
2015	PECAN	Plains Elevated Convection at Night	Great Plains	Nocturnal MCS
2016	Nederland	Nederland Fire	Colorado	Fire
2016	TWIRL 2016	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2017	SNOWIE	Seeded Natural Orographic Wintertime Clouds: Idaho Experiment	Idaho	Orographic cloud seeding
2017	TWIRL 2017	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2017	Eclipse	Eclipse	Wyoming	Solar eclipse effect on BL
2018	TWIRL 2018	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2018	GRAINEX	The Great Plains Irrigation Experiment	Nebraska	Effect of irrigation on BL
2018	RELAMPAGO	Remote Sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations	Argentina	Severe convection in Argentina
2019	TWIRL 2019	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2020	Colo Fires	Colorado Fires	Colorado	Fires
2021	TWIRL 2021	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2022	WINTRE-MIX	Winter Precipitation Type Research Multi-scale Experiment	Northern New York and Southern Quebec	Project to study mixed precipitation in near-freezing environments and the multi-scale processes that influence precipitation type.
2022-2023	PERiLS	Propagation, Evolution and Rotation in Linear Storms	Southeast	QLCS Tornadoes
2022-2023	LEE	Lake Effect Electrification	New York	Lake effect storms and lightning
2024	BEST	Boundary-layer Evolution and Structure of Tornadoes	Great Plains	Tornadoes

Doppler on Wheels 8 (Configurable Radar On Wheels)

The Configurable Radar On Wheels (CROW) was designed to be a versatile mobile radar platform able to change radars depending on the research project. It was first deployed in 2012 with a rapid scan phased array radar previously used on DOW 5, but was shortly thereafter upgraded to carry a single polarization X-Band radar used on DOW 2 and 6. In late 2024, the CROW was upgraded again to carry a 1.5 degree beam dual polarization C-band radar, similar to those mounted on SMART-R research vehicles. Like DOW's 6 and 7, the CROW is built on a 7500 series International Workstar Truck.

Single Polarization X-Band Configuration

DOW 8 Single Polarization

Country of origin	USA
Designer	Joshua Wurman
No. built	1
Type	Weather Radar
Frequency	X-band
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 0.93°
Pulsewidth	0.167 - 1.0 μs
Power	250 kW (Peak Tx Power)

The Single Polarization configuration of DOW 8 utilizes the radar first fielded on DOW 2, which is only able to scan horizontally or vertically at a single time. Because of this, it uses a singular 250 kW generator to power the singular frequency used when scanning. While not as advanced as the dual polarization radars on DOWs A and B (previously 6 and 7), it is still incredibly valuable during research deployments and allows for the creation of a 3 X-band radar network that provides more extensive coverage and allows for dual doppler wind velocity analysis. This versatility has has been utilized on several large NSF research projects, including Plains Elevated Convection at Night 2015 (PECAN), The Great Plains Irrigation Experiment 2018 (GRAINEX), Remote sensing of Electrification, Lighting, And Mesoscale/microscale Processes with Adaptive Ground Observations 2018 (RELAMPAGO), and Propagation, Evolution and Rotation in Linear Storms 2022 (PERiLS).

DOW 8 Radar Specifications

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	500–6000 Hz (+stagger)
Polarization	H or V
Processing	TITAN
Products	V, Z, SW, NCP, IQ
Antenna Scan Speed	0 - 50°s - 1
Antenna Scan Modes	PPI, RHI, SUR, Solar

DOW 8 Single-Pol Research Missions

Year	Name	Full Name	Location	Focus
2015	PECAN	Plains Elevated Convection at Night	Great Plains	Nocturnal MCS
2017	TWIRL 2017	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes
2018	GRAINEX	The Great Plains Irrigation Experiment	Nebraska	Effect of irrigation on BL
2018	RELAMPAGO	Remote Sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations	Argentina	Severe convection in Argentina
2022	PERiLS	Propagation, Evolution and Rotation in Linear Storms	Southeast	QLCS Tornadoes

Rapid Scan Configuration

DOW 8 Rapid Scan

Country of origin	USA
Designer	Joshua Wurman
Introduced	2012
No. built	1
Type	Weather Radar
Frequency	9.3-9.8 GHz (X-band)
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 0.8°
Pulsewidth	0.1 - 1.0 μs
Power	40 kW (Peak Tx Power)
Other names	RS DOW, Rapid Scan DOW

The DOW 8 Rapid Scan configuration utilizes the same radar used on DOW 5, but boasts an upgraded chassis and new processor, upgrading from the PIRAQ-3 to Thunderstorm Identification, Tracking, Analysis and Nowcasting (TITAN). It still maintains the frequency based, electronic vertical steering phased array radar that has a peak transmit power of 40 kW, but the radar is now mounted on a small elevator system. This elevator system allows for the radar and its pedestal to be raised while stationary, reducing radar beam blockage from the cabin.

DOW 8 Rapid Scan rear profile

DOW 8 Rapid Scan Radar Specifications

Tx Power (Peak)	40 kW
Phased Array Dimension	2.4 m x 2.6 - 3.0 m
Beamwidth (3 dB)	0.8° x 0.9° (6 beams, upgradable to 12)
Pulsewidth (μs)	0.125 - 1.0 μs
Gatelength	11 - 600 m (0.2 - 2 μs)
PRF	500-6000 Hz (+stagger)
Polarization	H or V
Processing	TITAN
Products	V, Z, SW, NCP, IQ
Antenna Scan Speed	0 - 50°s - 1 (7 second volumes)
Antenna Scan Modes	PPI, RHI, SUR, Solar

DOW 8 Rapid Scan Research Missions

Year	Name	Full Name	Location	Focus
2012	ROTATE-2012	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	ROTATE-2013	Radar Observations of Tornadoes and Thunderstorms Experiment	Great Plains	Dual-Doppler tornado radar scans and probe deployments
2013	OWLeS	Ontario Winter Lake-effect Systems	New York	Lake effect storms
2016	TWIRL 2016	Tornadic Winds: In-situ and Radar observation at Low levels	Great Plains	Tornadoes

C-band Configuration

Mini-COW

Country of origin	USA
Designer	Joshua Wurman
Introduced	2024
No. built	1
Type	Weather Radar
Frequency	C-band
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 1.5°
Pulsewidth	0.15 - 1.0 μs
Power	1000 kW (Peak Tx Power)
Other names	DOW 8 C-band, COW2

The Mini-COW configuration of DOW 8 was designed to fit a C-band radar on a Doppler on Wheels while also maintaining the maneuverability and short deployment times of the CROW and other X-band DOWs. C-band radars are useful because they serve as an intermediate frequency between S-bands and X-bands, gaining some of the benefits of each. C-band radars have longer ranges than X-band radars and are less susceptible to clutter, meaning they can scan through more precipitation and experience less attenuation degradation. However, C-band radars have lower overall resolution than X-band radars because of their longer wavelength. This makes C-band radars ideal for high precipitation events like hurricanes, mesoscale convective systems, squall lines, and supercells. When paired up with X-band DOWs and the larger COW, the FARM Facility can get a more comprehensive view of severe weather by having both smaller scale high frequency data and a better overall view of precipitation and velocity throughout an entire storm system.

Like the SMART-R mobile C-band radars, the Mini-COW utilizes a beamwidth of 1.5 degrees while also incorporating newer and more advanced technologies. These newer technologies allow for the Mini-COW to have a lower pulsewidth range of 0.15 - 1.0 μs compared to the 0.2 - 2.0 μs of SMART-R's 1 and 2, which gives the Mini-COW an overall higher resolution at the slight cost of range. This is compensated for by the Mini-COW having a significantly higher peak transmit power of 1 MW compared to the SMART-R's 250 kW, allowing for better precipitation penetration.

Mini-COW Radar Specifications

Tx Power (Peak)	1000 kW
Antenna Dimension	Unknown
Beamwidth (3 dB)	1.5°
Pulsewidth(μs)	0.15 - 1.0 μs
Gatelength (m)	12.5 – 600 m
PRF	500 – 6000 Hz (+stagger)
Polarization	Dual-Frequency Dual-Polarization
Processing	TITAN
Products	ZDR. ρHV, V, Z, SW, NCP, IQ
Antenna Scan Speed	50 deg/s−1
Antenna Scan Modes	PPI, RHI, SUR, Solar

Mini-COW Research Missions

Year	Name	Full Name	Location	Focus
2025	ICECHIP	In-situ Collaborative Experiment for the Collection of Hail In the Plains	Great Plains	Hail

C-band on Wheels

COW

Country of origin	USA
Designer	Joshua Wurman
Introduced	2018
No. built	1
Type	Weather Radar
Frequency	C-band
PRF	500 - 6000 Hz (+stagger)
Beamwidth	(3dB) 1°
Pulsewidth	0.167 – 1.0 μs
RPM	24 deg/s-1
Power	2x 1000 kW (Peak Tx Power)

The C-band on Wheels (COW) was completed in 2018 and designed to create a quickly deployable C-band platform that avoids compromises made by other mobile, quickly deployable (MQD) doppler radars. Traditional MQD radars use parabolic antennas smaller than 2.5 meters to fit under bridges and underpasses, meaning mobile radars are generally built to operate from 3 mm W-band wavelengths to 3 cm X-band wavelengths. Smaller wavelengths allow for the detection of smaller particles and higher resolutions, but are also much more susceptible to clutter, contamination, and attenuation. This forces them to operate at extremely close ranges, limiting deployment opportunities and increasing the chance of unsuccessful data collection missions, especially when studying high precipitation events like supercells. While several W-band and Ka-band mobile doppler radars exist, most notably the UMASS W-band and Texas Tech TTUKa (Ka-band), most MQD operate within the X-band because it still offers high-frequency performance while suffering from significantly less attenuation and can operate at longer ranges. X-band MQD radars include the DOW Network, NO-XP, MAX, RaXPol, UMass X-Pol, MWR-05XP, and Atmospheric Imaging Radar (AIR).

However, mobile X-band radars still suffer from attenuation, especially in high precipitation systems. This is most noticeable in areas behind the hail core and rear flanking downdraft. This can be addressed by using mid-band radars, which have longer wavelengths that are able to penetrate deeper through precipitation. The problem with using mid-band radars for MQD platforms is that they generally require antennas longer than 2.5 m to maintain high resolutions comparable to those of X-band radars. SMART-R mobile radars chose to compromise overall resolution by fitting a 2.4 m parabolic antenna that has a beamwidth of 1.6 degrees, but those compromises created resolution volumes over 2.5 times larger than those produced by X-band radars with 0.93 degree beamwidths.

Rear view of C-band radar

COW Radar Specifications

Tx Power (Peak)	2x 1000 kW
Antenna Dimension	3.8 m Parabolic
Beamwidth (3 dB)	1.05°
Pulsewidth (μs)	0.167 - 1.0 μs
Gatelength	12.5 - 600(0.08 - 2 μs)
PRF	500–6000 Hz (+stagger)
Polarization	dual-frequency, dual-polarization
Processing	TITAN
Products	LDR, ZDR, ρHV, V, Z, SW, NCP, IQ
Antenna Scan Speed	0 - 24°s - 1
Antenna Scan Modes	PPI, RHI, SUR, Solar

To avoid making compromises in resolution like the SMART-R, the COW chose to use a 3.8 m parabolic antenna that is is powered by a pair of 1 MW generators. This allows for the COW to have high resolution and high precipitation penetration at long ranges, but comes at the COW's ability to move once deployed. The COW's dish and antenna are split in half while being transported, and need to be assembled and disassembled during and after each deployment. This is done with a built in crane, and requires several people operating the COW to help construct and place the antenna onto the pedestal. The process takes 2 hours to set up and another 2 hours to disassemble, meaning it takes a 4 hours in total to deploy. This limitation means the COW can usually be deployed only once per day, but the benefits from large radar allow the COW to fill niches that were previously impossible for quickly deployable radars.

COW deployment strategies

The COW's long range dual polarized radar with a narrow beamwidth of 1.05 degrees makes it ideal for targeted studies where the radar changes locations between IOPs, longer period stationary deployments, and even allows it to serve as a gap filling radar. During the PERiLS project, which was a targeted study of QLCS tornadoes that required the COW to change locations every IOP, the radar operated with a scan radius of ~90 km (180 km diameter) and paired with other mobile radars to create a broad radar array network. Because of their greater range and less susceptibility to attenuation, C-band radars made up the backbone of the radar network. The COW operated as the central radar, with 2 SMART-R radars being spaced 35 km from the central COW. Higher frequency X-band radars, consisting of DOW 6, DOW 7, NO-XP, MAX, and occasionally DOW 8, functioned as baseline extenders for the SMART-R radars, especially in areas with poor site suitability. The X-band radars were spaced 25 km apart from each other and the SMART-Rs. This setup, enabled by the COW, allowed for high resolution radar data across a large geographic area in a way that would previously not be possible.

COW Research Missions

Year	Name	Full Name	Location	Focus
2018	RELAMPAGO	Remote Sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations	Argentina	Severe convection in Argentina
2022	WINTRE-MIX	Winter Precipitation Type Research Multi-scale Experiment	Northern New York and Southern Quebec	Project to study mixed precipitation in near-freezing environments and the multi-scale processes that influence precipitation type.
2022-2023	PERiLS	Propagation, Evolution and Rotation in Linear Storms	Southeast	QLCS Tornadoes

Capabilities

As of May 2024, the current operational Doppler on Wheels vehicles include the CROW (which consists of the DOW8/RSDOW/Mini-COW), 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. 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, and the Mini-COW, utilizing a singular 1 MW C-band transmitter capable of 50-second dual-polarization updates.

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. 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. 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.

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), and the largest tornadic circulation ever documented (the Cimarron City–Mulhall–Perry Tornado, which also occurred on 3 May 1999), 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.

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.

Gallery

• 
  DOW 7 at PECAN 2015
• 
  C-Band on Wheels
• 
  C-Band on Wheels Generator

See also

• Mobile radar observation of tornadoes
• Bistatic radar
• Pulse-Doppler radar
• Storm chasing
• Joshua Wurman
• Karen Kosiba

External links

• Information on Doppler on Wheels and Rapid DOW