<title>Thermovision method for the investigation of initiation and spread of a surface forest fire</title>

Abstract

Surface forest fires (SFF) is the most common natural type of the forest fire causing a great ecological and economic damage. Although quite a lot of experimental works have been devoted to an investigation of SFF, a problem of a dominating mechanism of transferring energy from the zone of reaction to a forest fuel has not been solved yet. Exact profiles of the combustion product concentrations in the fire front are not known, and limiting conditions of its spread have not been properly investigated. To detect forest fires passive optico- electronic systems located on space apparatus are coming into use. However, to estimate the efficiency of space techniques, identification methods, classification and prediction of the forest fire development it is necessary to know thermal flows in the assigned spectral intervals, attenuation of an irradiation by an atmosphere, by particles of smoke and crowns of the trees, efficient combustion areas depending on the type of the fire and some other characteristics. Besides, it is necessary to take into account that a combustion process of the forest fuels depends on their density, moisture content, initial temperature and humidity of the air as well, speed and direction of the wind, the angle of terrain relief slope. Investigation of SFF in the natural, large scale experiments is complicated because of the bad reproduction of the results and considerable dependence of the combustion parameters on external factors. In general this problem is solved by means of laboratory devices which allow to model partly the conditions of the surface forest fire initiation and spread. For example, in the works set-ups for physical modeling SFF in specialized aerodynamic pipes are described. However, this method has unavoidable drawback caused by the fact that a real process of the forest fuel combustion in an open space is modeled by a combustion of the forest fuel in a half-closed space where the experiments are made. Closeness of the space in specialized aerodynamic pipes results in a change of temperature and composition of the medium and influences velocity fields of the fire front as a result of the traction force change in the area of SFF. Hoover, experimental works on investigation of the fires in laboratory conditions continue, new laboratory set-ups being made allowing to exceed the range of investigating forest fuel combustion with more exact approximation to the real conditions. In contrast to the natural investigations laboratory experiments can be carried out all the year round with less material expenses.3122