One of the worst airplane disasters in history occurred as a consequence of a series of unfortunate events. The location of the disaster was the island of Tenerife, the largest and most populated island of the Canary Islands, on March 27th, 1977. Two Boeing 747 planes prepared for departure on a crowded runway where they were instructed to follow a procedure called “backtaxi” where a portion of the runway is used as a taxiway for aircraft to taxi in the opposite direction from which they will take off. Through a series of misinterpreted communications between air traffic controllers and the pilots, one of the planes began their take off before the other, backtaxiing plane had cleared the same runway. Dense fog shrouded the planes from sight and they did not realize that they were barreling towards disaster until they were 2,000 feet from each other. A detailed account of the events of this fateful day can be found here.
Computer rendering of the Tenerife disaster. Source: http://www.nycaviation.com
Of all the events that led up to the disaster, the straw that broke the camel’s back was a dense layer of fog that clouded the two planes from each others', and the air traffic controller’s, vision. Unfortunately, the small airport on Tenerife was not equipped with ground-based radar, a tool that would have allowed the controllers to see the location of the planes even with the heavy cover of fog. Although this disaster happened 35 years ago, ground-based radar technology was already available, in fact, this technology was developed long before 1977.
The interest in radar systems exploded during World War 2 as several countries realized the value of radar which could detect incoming enemy warplanes, control antiaircraft gunfire, navigate ships, and guide airplanes. In fact, one of the first radars developed by the United States (SCR-270) actually spotted the Japanese warplanes headed towards Pearl Harbor, but the sightings were shrugged off as U.S. planes.
SCR-270 Radar preserved at the National Electronics Museum. Source: http://www.todaysengineer.org
Although radar is often associated with weather these days, precipitation detection via radar was actually an unintentional discovery. Radar engineers during WW2 realized that storms appeared as large, moving clusters on their screens, which would obscure the intended ship or aircraft targets. Following this discovery, dozens of meteorologists were trained in radar technology and surface-based and airborne weather radar observations were established by 1943.
After the war, technological advances on radar slowed, but governments across the world continued weather radar research. Left over military radars from WW2 were used by the weather service of the U.S. The WSR-57 (Weather Survelliance Radar – 1957) was the first generation of radars specifically designed for a national warning network. The WSR-57 was an improvement on earlier radar technology as it provided more detailed information about storm strength, however, the reflectivity data was still very coarse and the inclusion of velocity data did not occur until the full development of the Doppler radar. In 1974, the network of radars was expanded with the WSR-74 (Weather Surveillance Radar – 1974) which were an updated version of the WSR-57. The WSR-74’s filled in gaps across the country that were not covered by the WSR-57 network, improving forecasts and severe weather warnings.
Radar image from the WSR-57 at the Twin Cities Weather Bureau Office in Minnesota: Source: NOAA
The utility of the Doppler frequency shift for radar was discovered before WW2, but it took several years to develop the technology to the point where it could be used for meteorological purposes. After years of study and development, the WSR-88D (Weather Surveillance Radar – 1988 Doppler) finally replaced the network of WSR-57 and WSR-74 radars in the early 1990’s. A network of 150 of these WSR-88D or NEXRAD (Next Generation Radar) were spread out across the country providing forecasters with detailed information from storms including hail, tornadic signatures, downbursts, gust fronts, and precipitation measurements. Today, Doppler radar is the primary radar used by meteorologists in the U.S.
Picture of a WSR-88D from Rapid City, SD. Source: NWS
Various software upgrades have been applied to the WSR-88D, in fact, by the end of 2012 the entire fleet of radars is scheduled to have the biggest radar system upgrade since the WSR-88D was fielded. According to the National Weather Service, “This upgrade, known as dual-polarization technology, will greatly enhance these radars by providing the ability to collect data on the horizontal and vertical properties of weather (e.g., rain, hail) and non-weather (e.g., insect, ground clutter) targets.”
Diagram of how the Dual-Polarization upgrade to the WSR-88D will work
Radar has a wide range of applications, developed initially as a tool of war and ending up as a staple of the meteorologist's weather segment on the evening news. Radar technology has helped not only in war and weather, but has far-reaching implications for fishermen, police, bird watchers, astronomers, and air traffic controllers, to name a few. The perfect storm of events that led up to the horrific airplane collision of 1977 in Tenerife could have been avoided had the airport been equipped with ground-based radar. Radar would have been able to "see" through the dense fog to alert the air traffic controllers that the two airplanes were on a collision course of historic proportions.
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