Influence of the canopy structure of a birch forest on the visibility of the fires below

The work is aimed at studying the visibility of a flame through the canopy of a birch forest, depending on the structure of the latter, and providing support for decision-making on the choice of the optimal sensing geometry for solving the problem of detecting fires in birch forests when video shooting from low altitudes. For the site located in the Priozersk district of the Leningrad region, using photographic technology, data were obtained on the frequency distribution of birch leaf inclination angles (for a hybrid of two species). The information is compared with the results of the work of other researchers. On the basis of the collected data, three-dimensional models of the canopy of various structures were constructed, suitable for simulating the radiation transfer. A set of experiments has been carried out to estimate the values of the fraction of beam penetration for light emitted by the combustion center in the direction of the sensor at different viewing angles. For individual ratios of crown sizes and distances between them, the least informative ranges of viewing angles, which should be avoided when monitoring fires, have been determined. It has been confirmed that the visibility of the flame depends on the shape and closeness of the crowns, which determine the length of the radiation path in the vegetation layer, and, to a lesser extent, on the prevailing orientation of the leaves.