Lightning detector

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Lightning detector at the Kennedy Space Center in Florida.

A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location (often aboard an aircraft), and space-based systems.

Ground-based and mobile detectors calculate the direction and severity of lightning from the current location using radio direction-finding techniques together with an analysis of the characteristic frequencies emitted by lighting. Ground-based systems use triangulation from multiple locations to determine distance, while mobile systems estimate distance using signal frequency and attenuation. Space-based lighting detectors, on artificial satellites, can locate range, bearing and intensities by direct observation.

Ground-based lightning detector networks are used by meteorological services like the National Weather Service in United States and the Meteorological Service of Canada, and by other organizations like electrical utilities and forest fire prevention services.

1 Limitations
2 Lightning detectors vs. weather radar
3 Aviation use
4 Personal lightning detectors
5 References
6 External links

[edit] Limitations

Each system used for lightning detection has its own limitations^[1]. These include:

A ground-based lightning network must be able to detect a strike with at least three antennas to locate it with an acceptable margin of error. This often leads to the rejection of cloud-to-cloud lightning, as one antenna might detect the position of the strike on the starting cloud and the other antenna the receiving one. As a result, ground-based networks have a tendency to underestimate the number of strikes, especially at the beginning of storms where cloud-to-cloud lightning is prevalent.

Since they use attenuation rather than triangulation, mobile detectors sometimes mistakenly indicate a weak lightning strike nearby as a strong one further away, or vice-versa.

Space-based lightning networks suffer from neither of these limitations, but the information provided by them is often several minutes old by the time it is widely available, making it of limited use for real-time applications such as air navigation.

[edit] Lightning detectors vs. weather radar

A thunderstorm life cycle and associated reflectivities from a weather radar

Distribution of electric charges and lightning strikes in and around a thunderstorm

Lightning detectors and weather radar are complementary to detect storms. Lightning detectors indicate electrical activity, while weather radar indicates precipitation. Both phenomena are associated with thunderstorms and can help indicate storm strength.

The first image on the right shows the life cycle of a thunderstorm:

Air is moving upward due to instability.
Condensation occurs and radar detects echoes above the ground (colored areas).
Eventually the mass of rain drops is too large to be sustained by the updraft and they fall toward the ground.

The cloud must develop to a certain vertical extent before lightning is produced, so generally weather radar will indicate a developing storm before a lightning detector does. It is not always clear from early returns if a shower cloud will develop into a thunderstorm, and weather radar also sometimes suffers from a masking effect by attenuation, where precipitation close to the radar can hide (perhaps more intense) precipitation further away. Lightning detectors do not suffer from a masking effect and can provide confirmation when a shower cloud has evolved into a thunderstorm.

Lightning may be also located outside the precipitation recorded by radar. The second image shows that this happens when strikes originate in the anvil of the thundercloud (top part blown ahead of the cumulonimbus cloud by upper winds) or on the outside edge of the rain shaft. In both cases, there is still an area of radar echoes somewhere nearby.

[edit] Aviation use

Large airliners are more likely to use weather radar than lightning detectors, since weather radar can detect smaller storms that also cause turbulence; however, modern avionics systems often include lightning detection as well, for additional safety.

For smaller aircraft, especially in general aviation, there are two main brands of lightning detectors (often referred to as sferics, short for atmospherics): Stormscope, produced originally by Ryan (later B.F. Goodrich) and currently by L-3 Communications, and the Strikefinder, produced by Insight. Lighting detectors are inexpensive and lightweight, making them attractive to owners of light aircraft (particularly of single-engine aircraft, where the aircraft nose is not available for installation of a radome).

[edit] Personal lightning detectors

A StrikeAlert personal lightning detector.

One type of lightning detector slowly increasing in popularity is the battery-operated personal lightning detector. Similar in size to a pager, personal lightning detectors are popular among golfers, campers, law enforcement, sports officials and other persons who work or recreate outdoors. Personal lightning detectors function by detecting the electromagnetic pulse emitted by a lightning strike. By measuring the strength of the detected EMP, the device can then estimate how far away the detected strike was. When exposed to multiple detected strikes, some personal lightning detectors can even calculate and extrapolate the direction of the storm's movement relative to its position (approaching, departing or stationary).

Although personal lightning detectors do function well in regards to their ability to detect nearby lightning, they are quite basic in functionality when compared to professional lighting detectors. For example, they cannot tell where a lightning strike was located or from which direction the lightning is approaching, only that lightning is in the area. Also, since a personal lightning detector is triggered by EMPs, interference from other EMP-emitting devices (such as electronic equipment, appliances, fluorescent lights and even car engines) can sometimes result in either false alarms or missed strikes. This interference often has the additional effect of preventing personal lightning detectors from functioning properly while indoors. Despite these limitations, personal lightning detectors continue to increase in popularity among individuals and professionals.