In this study, a theoretical formulation of the ignition and combustion of the wood layer by burning and smoldering firebrands has been considered. The effect of the firebrands’ length, distances between firebrands and their geometrical parameters on the heat exchange with the wood layer and the ignition process were analyzed. With a decrease in firebrand size, ignition of wood is possible with a decrease in the distance between the firebrands. With an increase in firebrand size at the same distance between them, the ignition regime becomes possible albeit with a longer delay time Δt. With a decrease in the distance between the firebrands, the ignition of wood is possible with an increase in Δt. As a result of mathematical modeling of the process, the following processes are noted: the heat stored in firebrands of small sizes is insufficient to initiate the ignition process; the temperature in the wood layer, due to conductive heat exchange, slightly increases at first, before beginning to decrease as a result of heat exchange with the surrounding air and the wood layer; intensive heat exchange with the environment of small size firebrands leads to the end of firebrand smoldering and its cooling; and, if the firebrand size reaches a critical value, then the pyrolysis process begins in the area adjacent to it.

An infrared diagnostic of the scale of turbulence in the front of a natural fire is presented, as well as a comparison with the scale of turbulence in the air near the combustion source for a model grassland and crown fire. An analysis of the flame of a grassland fire reveals smaller turbulence scales than the flame of a crown fire. A fire-induced atmospheric turbulence at a height of 10 m is observed with the corresponding frequency of air temperature pulsation (0.1–6 Hz for a steppe fire and 0.1–3 Hz for a crown fire). The values of the structural functions of refractive index and temperature fluctuations are significantly higher than the background values and can be used for remote fire detection.