Optimisation of location and number of lidar apparatuses for early forest fire detection in hilly terrain

It has recently been shown that lidar (LIght Detection and Ranging) can effectively detect smoke plumes from small bonfires up to distances of 6.5 km, so that the technique can be used for wildfire surveillance. The aim of the present work is to describe a method for calculating the optimal location and minimum number of lidar stations required for the surveillance of a given forest area, taking the hilly terrain of Sintra-Cascais Nature Park (Portugal) as an example. The placement and horizontal scanning of the lidar sensors must be such that the laser beam passes over the ground, while keeping sufficiently low to enable early smoke plume detection, before the smoke is dispersed by the wind. Simultaneously, the laser beam should not hit the ground at distances shorter than the instrument range. To solve the problem, a terrain rendering was created and the best laser-beam zenith angle for each azimuth and the effective range covered by each lidar were calculated. The computations showed that 95% of the 146 km2 of the Nature Park area can be covered by seven detectors with the laser beams scanning at a height of 50 m or less above ground.