A lightning prediction system detects atmospheric conditions likely to produce lightning strikes in a certain area and sounds an auditory alert, warning those nearby that lightning is imminent and giving them the chance to find safety before the storm actually impacts the area. Lightning protection systems are often installed in outdoor areas which are often congested with people, lack sufficient substantive shelter, and are difficult to evacuate quickly (such as water parks, college campuses, and large swimming pool or athletic field complexes) as these locations are particularly dangerous during lightning storms.
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The first lightning prediction system, the Lightning detector, was invented in 1894 by Alexander Stepanovich Popov. It also was the first Radio receiver in the world.
The detection equipment is designed to constantly survey atmospheric electrical activity and potential for lightning occurrence via radar and other methods. Storms are scanned by radar in one or more orthogonal polarizations and the co-polar and cross-polar returns are correlated coherently and incoherently. The correlation coefficient is examined to determine the degree electrification and potential for lightning occurrence.
The method used by such systems includes the stationing of at least three receivers at known geographic locations in spaced relationship to each other in order to triangulate their data. When any of the receivers detects a strong electrical disturbance in the immediate atmosphere, the location is stored locally, shared with other receivers in the area for corroboration, and then (presuming the data has passed the filters), encoded and transmitted to a central facility and thereafter processed for deriving the position of the lightning strike. By detecting thunderstorm electrical fields before they actually enter the area protected by the system, a track can be postulated, allowing for warnings to be sounded as early as 30 minutes before any lightning actually strikes the protected area. The system is synchronized with the U.S. Coast Guard LORAN navigation network, and includes various features which permit a more accurate analysis of lightning position.
While some systems require manual remote activation of the auditory alert siren from the central monitoring facility, others (including the most commonly used, the Thor Guard) are capable of automatically sounding the auditory "Seek Shelter Now" alert when pre-determined conditions for electrical disturbance strength, proximity, and data corroboration from other units are met. Likewise, Thor Guard is capable of sounding an "All Clear" tone when electrical activity in the monitored area has receded to safe (background) levels. This feature eliminates both the need for 24/7 skilled monitoring of the system as well as the chance for human error in deciphering the data (such as calling an alert too late or not at all, or calling an All Clear before the danger has truly passed)