Comparison of eye-safe UV and IR lidar for small forest-fire detection

摘要

Lidar is a promising tool for forest-fire monitoring because this active detection technique allows efficient location of tenuous smoke plumes resulting from forest fires at their early stages. For the technique to be generally usable, instrumentation must be eye-safe, i. e. it must operate within the spectral range λ<0.4 or λ>1.4 μm. In this paper the lidar efficiency at the wavelengths 0.3472 μm (second harmonic of the ruby laser) and 1.54 μm (Er:glass laser) are compared using a theoretical model. The results of calculations show that the energy required for smoke-plume detection using 0.3472 μm becomes greater than the corresponding value for 1.54 μm when the distance exceeds some threshold, which ranges between 2 and 6 km depending on other parameters. Being caused by relatively higher absorption of the UV radiation in the atmosphere, this result is valid for any wavelength in the vicinity of 0.35 μm, for example, the third harmonic of Nd:YAG laser and the second harmonic of Ti:sapphire laser.