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Lidar detects small forest fires

17 Jun 2002

Early detection of small forest fires is made easier with a simple lidar system.

Portuguese scientists have demonstrated the first early detection of small forest fires using a simple lidar system. They have reliably identified forest fires from 6.5 km away (Appl. Phys. B. 74 77).

Because lidar is an active technique that detects smoke rather than fire, it has significant advantages over passive methods for fire detection. Conventional methods of fire detection include infrared imaging from a satellite or other air-based system where line-of-sight is essential, a problem lidar does not suffer from.

Rui Vilar, who leads the research being carried out at the Instituto Superior Técnico, explained: "Small forest fires are defined in terms of the burning rate rather than the smoke-plume dimensions. In our work, a 'small forest fire' corresponds to a burning rate in the range 0.02 to 10 kg/s."

Using 10 ns pulses from a frequency-doubled Nd:YAG operating at 532 nm, the researchers have successfully identified small forest fires up to distances of 6.5 km. The fires were produced by burning dry olive logs at a rate of just 0.02 kg/s.

For increased rates of 2 kg/s and 10 kg/s, the researchers say the system can detect forest fires up to distances of 17 km and 23 km respectively in good weather conditions. Vilar claims that the predicted detection ranges of 10 - 23 km are similar or better than the range of the best ground-based systems for fire detection.

With dimensions of 0.5 x 0.75  x 1.5 m and weighing 300 kg, the researchers say that the system is not transportable in its mounted form. "The system is too large and heavy. We are developing a compact, eye-safe system based on an Er:glass laser that is portable and consumes less power," said Vilar.

The team is also developing algorithms for automatic recognition of smoke signatures in the lidar system. This cost-effective, single-wavelength technique will serve as the basis for future industrial developments. The researchers have a patent pending on the system and plan to commercialize the technique.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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