01 October 2002
Smokey the bear says, 'Only magnetic direction finding. . . .'
Tucson, Ariz.-Wildfires are roaring in the U.S. this summer. So far, they've consumed nearly 700,000 acres of forest and contents.
In the past there were fire towers perched high above their surroundings that afforded, sometimes, 100-mile vistas. People sat in these towers during the summer months, scanning the treetops for signs of smoke, as a decidedly low-tech early warning system.
Few of these 5,000 towers remain in the U.S. Though fairly effective, they are hard to man. Besides, one of the millions of Americans walking around with a cell phone spots and reports most forest fires.
Earlier detection, of course, is better. While many fires start because some nut, fool, or misguided individual is at work, most start as the result of a lightning strike.
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Faster than a speeding bullet Lightning strike locations are determined in about 30 seconds — faster than other hazardous weather indicators — making it an important early warning tool. The accuracy of the network depends on precise waveform processing, global positioning system time synchronization, high-speed signal processing, and wideband peak gated magnetic direction finding techniques.
Source: www.lightningstorm.com |
Vaisala-GAI operates this National Lightning Detection Network (NLDN). It consists of 114 remote, ground-based sensing stations located across the U.S. that instantaneously detect the electromagnetic signals given off when lightning strikes the earth's surface.
Together with a similar 87-sensor Canadian system, Vaisala operates the largest cohesive lightning detection network ever deployed, covering 90% of the total land area in North America.
These remote sensors send the raw data via satellite to the company's network control center in Tucson, Ariz. Within seconds of a lightning strike, the center's analyzer processes information on the location, time, polarity, and amplitude of each strike.
The accuracy of the network depends on precise waveform processing, global positioning system time synchronization, high-speed signal processing, and wideband peak gated magnetic direction finding techniques.
The lightning information then transmits to users across the country.
Vaisala engineer Michael Austin said, "The sensors resemble a 6-foot-tall Q-Tip. Lightning strikes have a unique electromagnetic waveform, a fingerprint. Four to 12 sensors sense any strike. Using time of arrival and triangulation, the NLDN provides detection efficiency and locates the strikes within 500 meters.
"Users can see the data through a computer display within 15-20 seconds of a lightning event," he added. "By sensing ionospheric reflections, the system can home in on strikes 4,000 kilometers distant."
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NLDN sensor locations
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Their work attracted the attention of the Bureau of Land Management (BLM), which needed a way to detect lightning-caused forest fires in Alaska. A solution for the BLM's detection problem began operation in 1976.
The Lightning Location System, based on a University of Arizona patent, automatically and accurately located cloud-to-ground lightning over large areas.
The technology and its associated sensors, central processors, and analytical software applies in such industries as aerospace and defense, electric power utilities, meteorology, aviation, mining, golf and recreation, and insurance.
The NIFS incorporated the NLDN into its 2-year old system that collates and maps all the information and resources it needs to fight fires. The map is now an interactive Web site that continuously updates, with intelligence that spans the gamut from satellites to personnel on the ground with shovels and hoses. IT
- Nicholas Sheble, nsheble@isa.org
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