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Normal Doppler radar reflectivity display showing squall line.October 29, 2004 — Who would have imagined that radar technology designed to detect and locate hostile aircraft and missiles in WWII would serve as the basis for today’s advanced weather radar systems. At that time, storms were a nuisance that obscured valuable data. Later, however, users realized the potential benefits of radar for weather detection. Now, the NOAA National Weather Service relies daily on radar to detect, locate and measure precipitation inside clouds. In fact, today's radars are so advanced they can even identify types of precipitation, detect important weather features that make a storm severe, and track and predict the motion of storms.

Antenna for new WSR-57 weather radars, the first of which was to be installed in Miami. In: Weather Bureau Topics, Febuary 1959, p. 27.NOAA National Severe Storms Laboratory
Much of the credit for modern weather radar systems should be given to the NOAA National Severe Storms Laboratory in Norman, Okla., which celebrated its 40th anniversary in mid-October. “We want to take this time to savor our accomplishments over these past 40 years and look optimistically toward the future,” said James F. Kimpel, NSSL director.

NSSL Background
Established in 1964, the NOAA NSSL leads the way in investigating all aspects of severe and hazardous weather. NSSL is part of NOAA Research and is the only federally supported laboratory focused on severe weather. NSSL’s scientists and staff explore new ways to improve understanding of the causes of severe weather and how to use weather information to assist NOAA National Weather Service forecasters, as well as federal, university and private sector partners.

Weather Radar Research
Hurricane Carla as seen by WSR-57 radar at Galveston, Texas. Arrow designates location of tornado which occurred near Kaplan, Louisiana. Monthly Weather Review, December 1962, p. 515.The very foundation of today’s NSSL lies in weather radar research and development that began before the lab’s origin in 1964. Two years earlier, the National Severe Storms Project had established its Weather Radar Laboratory in Norman, Okla. This facility became a major component of the new NSSL. Part of NSSL’s initial role was to maximize the use of the original WSR-57 surveillance radars for the U.S. Weather Bureau (now the NOAA National Weather Service).

For the first few years, NSSL collected data on Oklahoma spring storms using the WSR-57. The WSR-57 weather radar worked by sending out short bursts of energy in a beam that came from a slowly rotating antenna. When the beam hit particles the size of rain, snow or hail some of the energy was reflected back to the antenna. If the particle was large, more energy bounced back. NSSL engineers made it possible to see the strength of the returned energy by creating a contoured black and white display. The Weather Bureau and most other radar users quickly adopted this technology because it provided more detailed information about storm strength.

The Weather Bureau's first experimental Doppler Radar unit. This radar was a 3-cm continuous wave Doppler unit obtained from the Navy and modified for meteorological purposes.Doppler Radar
In 1964, scientists were working to acquire additional radar technology. A 3-cm wavelength research Doppler radar was added to NSSL’s list of assets — a move that would revolutionize weather observation. This new radar allowed scientists to delve into and measure motion inside the storm for the very first time — providing valuable clues into the development of severe weather. A change in frequency occurred when a radar signal was reflected from a moving target, such as a cluster of raindrops – similar to the shift in frequency experienced with a passing sound (e.g., when a train blowing its whistle passes by). When they measured this shift in frequency, scientists could tell if particles were moving towards or away from the radar. It is this ability to discern internal air circulation that makes Doppler radar such a powerful weather-monitoring tool.

NSSL engineers developed real-time color displays in the late 1970's; here, Don Burgess points out details in Doppler reflectivity, velocigy and spectrum width data.Scientists and engineers soon discovered the 3-cm radar was not powerful enough for a large-scale storm surveillance network, and NSSL embarked on a program to develop a much stronger 10-cm Doppler radar. In 1969, NSSL was able to obtain and upgrade a surplus 10-cm radar that had been used by the U.S. Air Force.

The 10-cm Doppler radar in Norman became operational during the 1971 spring tornado season. Data were collected on magnetic tapes and processed on a NASA computer weeks or even months later because there was no real-time capability.

Scientists made many significant discoveries using these data, but one of the most important was the discovery of the tornadic vortex signature. When a circulation begins to form, its winds blow raindrops in a signature pattern on the radar screen. In May of 1973, a devastating tornado tore through Union City, Okla., a town just west of Oklahoma City. For the first time, Doppler radar and storm intercept teams documented the entire life cycle of the tornado. In reviewing the data, researchers discovered that a small-scale Doppler velocity circulation appeared aloft even before the tornado descended to the ground — a feature that would allow forecasters to better warn the public of the impending danger.

A tornadic vortex signature, the small red and yellow area indicated by the arrow, is visible in this horizontal scan of Doppler velocity data from the Binger tornado on May 22, 1981.Additional research on thunderstorms led to the Joint Doppler Operational Project, which tested the warning potential of the Doppler radar. JDOP conclusively showed that Doppler radar had the potential to assist in issuing more accurate warnings, and more importantly, warnings with enough lead time for the public to find safe shelter.

Further Advances: Dual Doppler And Pulse-Pair Processing
In 1974, a second 10-cm Doppler radar was constructed 26 miles northwest of the Norman Doppler radar. Known as the Cimarron Doppler radar (because of its location), it provided “dual-Doppler” capabilities. With both radars, scientists could see the same storm from two different perspectives, and pioneered studies on the structure of tornadic storms at different levels. Other advances included color displays and the development of pulse-pair processing, an efficient computational algorithm that uses pairs of pulses to compute Doppler velocity and display them in real-time (instead of days later).

The top image shows a WSR-88D vertical cross-section of radar reflectivity; the bottom image shows how dual-polarization techniques can better identify and quantify precipitation types and areas. The bottom color scale progresses from light, moderate, to heavy rain through rain/hail mix, graupel/sleet, hail, dry and wet snow, and ice.Dual Polarization Technologies
Dual-polarization capabilities were added to the Cimarron Doppler radar in time for the 1985 spring storm season. Scientists had learned that when pulses were alternately polarized vertically and horizontally the return signal provided a clearer indication of cloud and precipitation particle size, shape and ice density — they could determine if the targets were round like hailstones or somewhat flattened like raindrops. This information had great potential to improve severe weather warnings.

NWS Implementation
NSSL’s research helped convince the NWS that Doppler radar was a crucial forecasting tool. Beginning in the mid-1980’s, NSSL worked to make Doppler radar data useful for NOAA NWS forecasters in preparation for a national deployment of the radars. During field programs like DopLight, Doppler radar and lightning data were provided in real-time to both the Oklahoma City Weather Forecast Office and local TV media. Various algorithms were developed to detect and notify forecasters of hail, severe thunderstorms, tornadic circulations, downbursts and gust fronts (the leading edge of rain-cooled air), and track the movement of storms. These algorithms were later combined with a color display system and became known as the Warning Decision Support System.

Largely based on this work, and JDOP, the national network of 150 WSR-88D (Weather Surveillance Radar- 1988 Doppler) radars, or NEXRAD (short for NEXt generation RADar) were deployed in the early to mid-1990’s, jointly developed and operated by the NOAA NWS, Department of Defense and Federal Aviation Administration throughout the United States and selected overseas locations. The NEXRAD project replaced the older WSR-57 radars and now provides comprehensive radar coverage of the United States.

In 1997, NSSL received a Gold Medal from the Department of Commerce for work leading up to and their support of the national NEXRAD deployment. All the while many other scientists worked to find valuable clues in the data that were being produced.

Eyewall crossing the Outer Banks southwest of Cape Hatteras. Other Advances In Doppler/NEXRAD Technology
During the 1990’s, NSSL designed and implemented software for NEXRAD’s Open Radar Product Generator. The ORPG processes Doppler radar data and generates products for use by NEXRAD customers. Other NSSL teams worked on NEXRAD’s Open Radar Data Acquisition Unit to improve how basic data is acquired and to allow for future enhancements as needs of the industry change.

NSSL’s 20 years of polarimetric weather radar research were rewarded in the fall of 2003 following JPOLE, the Joint Polarization Experiment. JPOLE proved the engineering design and quality of data provided by a polarimetric radar would benefit operational users. The NOAA NWS recently approved taking the first steps to upgrade all the WSR-88D Doppler radars in the NEXRAD network with polarimetric technology. Polarimetric capabilities will complement information the Doppler radars already provide on wind, precipitation and storm motion. Another important discovery was that dual-polarization improved rainfall estimates with the 25 WSR-88D radars in the western United States where radar beams were blocked by mountains.

The Collaborative Radar Acquisition Field Test or “CRAFT,” was another milestone as researchers from NSSL, the University of Oklahoma, the NWS Radar Operations Center, the University Corporation for Atmospheric Research-Unidata, Internet-2, and the National Climatic Data Center were able to prove that access to high-resolution data from multiple radars was technically possible and economically viable. As a result, high-resolution radar data from the national network of NEXRAD radars will soon be available over the Internet in real-time to government, university and private sector users.

NSSL is also heading a project to seamlessly mosaic all NWS and Department of Defense WSR-88D radars across the United States to provide the first high-resolution depiction of storms and quantitative precipitation estimates from coast to coast in real-time.

Mobile Doppler Research Radar
Moving radar technology in a different direction, NSSL (in partnership with the University of Oklahoma, Texas A&M and Texas Tech) developed and are using Shared Mobile Atmospheric Research and Teaching Radars (also known as “SMART-Radars”). SMART-Radars are mobile Doppler radars that can be placed in position as a storm is developing rather waiting for storms to occur within range of stationary radar systems. Two SMART-R’s have already been used to study tornadoes, hurricanes and other weather phenomena across the country.

Phased-Array Radar
NSSL (with the help of its partners, the Navy, Federal Aviation Administration, University of Oklahoma, Oklahoma State Board of Regents, National Weather Service, Lockheed Martin and Basic Commerce Industries) is now leading radar technology into the future with a facility dedicated to phased array radar research and testing in Norman, Okla. Phased array radar uses electronically controlled multiple beams and frequencies on a flat plate antenna (instead of a parabolic or bowl-shaped antenna), which reduces the scan time of weather systems from five to six minutes for NEXRAD radar to only one minute. Phased array radar can also scan the atmosphere at lower levels more effectively and has the capability to quickly re-scan areas with the most severe weather — potentially increasing forecasters' warning lead times. Data gathered from phased array radar will also be used to initialize computer models and improve forecasts. It is expected to take 10-15 years to move from research and development to technology transfer and deployment.

Through ingenuity and creativity spanning 40 years, NSSL engineers and scientists have taken technology to the edge. From the original WSR-57 research project to Doppler radar, NEXRAD, and now polarized and phased array radars, NSSL’s radar research has truly changed the face of weather.

Relevant Web Sites

New Radar Technology Can Increase Tornado Warning Lead Times

NSSL Archive of Stories

NSSL's Accomplishments

NSSL's Photo CollectionWSR-88D Radar FAQ's

Phased Array Radar Backgrounder

Overview of NEXRAD Products

Weather Radar








Media Contact:
Keli Tarp, NOAA Weather Partners, Norman, Okla., (405) 366-0451
Article Drafted by Susan Cobb, NSSL