Weather Radar Development
Radar technology originally designed to detect and locate hostile aircraft in World War II served as the basis for the advanced weather radar systems that are saving lives today. The NOAA National Weather Service relies daily on radar to detect, locate, and measure precipitation inside clouds.
NOAA National Severe Storms Laboratory
Established in 1964, NOAA’s National Severe Storms Laboratory (NSSL), in Norman, Oklahoma, has led the way in investigating all aspects of severe weather and played an important role in the development of modern weather radar.
Weather Surveillance Radar-57
Initially, NSSL collected data on Oklahoma spring storms using the Weather Surveillance Radar-57 (WSR-57) weather radar. This 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. The larger the particle, the 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.
Doppler Radar
In 1964, scientists added a three-centimeter wavelength research Doppler radar to NSSL’s list of assets — a move that would revolutionize weather observation. This new radar allowed scientists to measure motion inside storms for the very first time, providing 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. This ability to discern internal air circulation makes Doppler radar a powerful weather-monitoring tool.
In 1969, NSSL obtained and upgraded a surplus 10-centimeter radar from the U.S. Air Force. Using this technology in 1973, scientists were able to document, for the first time, the entire life cycle of a tornado. In reviewing data collected when a tornado tore through a town in Oklahoma, researchers discovered that a small-scale circulation was visible on the Doppler radar even before the tornado touched the ground—a feature that would allow forecasters to better warn the public of the impending danger.
Additional research on thunderstorms led to the Joint Doppler Operational Project (JDOP), 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-centemeter Doppler radar that provided “dual-Doppler” capabilities was constructed. With both radars, scientists could see the same storm from two different perspectives, which led to pioneering studies on the structure of tornadic storms at different levels.
National Weather Service Implementation
Doppler radar became a crucial forecasting tool for the National Weather Service Implementation. Beginning in the mid-1980’s, NSSL made Doppler radar data useful for National Weather Service Implementation forecasters. During field programs, Doppler radar and lightning data were provided in real-time to both the Oklahoma City Weather Forecast Office and local TV media. Tools were developed to detect and notify forecasters of hail, severe thunderstorms, tornadoes, and other severe weather and to track the movement of storms.
Based on the early work of the NSSL 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-1990s. The NEXRAD project replaced the older WSR-57 radars and now provides comprehensive radar coverage of the United States.
Works Consulted
NOAA Magazine. (2004). Weather Radar Development Highlight of National Severe Storms Laboratory’s First 40 Years. Retrieved online October 2, 2006, from: http://www.magazine.noaa.gov/stories/mag151.htm.