A screen of the system (image courtesy of Obayashi Corp)
A screen of the system (image courtesy of Obayashi Corp)
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Obayashi Corp developed an alarm system that warns of a possible lightning strike not only by sensing an approaching thunder but also by forecasting a sudden strike with two kinds of sensors.

The system, "Thunder Watcher," is expected to be used at civil engineering and construction sites. At such sites, if there is no high building, etc, a construction crane can be struck by lightning, and the electricity can be conducted to the ground via the hook, causing damage to people and objects around the crane.

The system can be used for preventing such damage as well as for ensuring the safety of workers, preventing heavy machines from being damaged by lightning, determining whether explosive can be used, etc. Obayashi has already confirmed the efficacy of the system at several sites.

Existing alarm systems measure the situation of lightning around a site with sensors and predict the approach of lightning to the site. However, a thunder cloud is sometimes rapidly formed near a site, and a lightning strikes without any precursor. The existing systems cannot predict this kind of lightning strike.

The Thunder Watcher uses two kinds of sensors. One is the "thunder cloud sensor," which is for monitoring the static electrical charge of clouds above a site. Its detection range is several tens of kilometers.

The thunder cloud sensor can monitor the electrical charge without any discharging phenomenon caused by a lightning strike. Therefore, it can predict a sudden lightning strike, which cannot be predicted only by monitoring the situation of lightning around a site.

The other is the "lightning strike sensor," which monitors a surrounding area of more than 100km. It measures electromagnetic waves generated by a discharging phenomenon and the strength and frequency of lightning strike.

With those sensors and the information about the location of lightning (heavy precipitation area) and the direction of its movement (the direction of wind in the sky), the system measures the degree of risk on a scale of one to four by using its own method.

An alarm is issued via e-mail, etc. And the degree of risk can be checked by a person who is not at the construction site or work office. When the lightning is away from the site, the system lowers the degree of alarm. And the workers use the information to decide how long they will stop the operation.