Substantiation of Airborne Laser Scanning Parameters for Assessing Understory Forest Fuels in Pine Stands

The paper substantiates the optimal technical parameters of air laser scanning (ALS) using unmanned aerial vehicles (UAVs) to assess the undergrowth components of forest plantations. The research was carried out on the territory of the Kaluga Forestry of the Kaluga region in medium-aged pine plantations (Pinus sylvestris L.) with a canopy closure of no more than 0.8. Flight survey work was carried out using a Luftera LQ-5 UAV and a Luftera LS-100 laser scanner (scanning frequency 320-640 thousand pulses /sec.; the rotation frequency of the scanning unit is 10-20 To identify the optimal shooting mode, a series of experimental flights were conducted with various parameters of speed and altitude, as well as the amount of overlap between routes. The study used conventional methodological approaches that are used both in on-site surveys and in the organization of flight and survey processes, as well as in the processing of materials in the office. Verification of the VLS data was carried out based on the materials of the field survey by comparing the quantity and category of the size of forest combustible materials (undergrowth, understory, and deadwood). Statistical analysis was performed using the parametric Student's t-test and the Pearson's goodness-of-fit test. The main criterion for determining the effectiveness of the selected VLS mode was the density of the cloud of points under the crowns of the forest stand (vertical cut height of 3 m). It has been established that a density of at least 100 points per m² under the canopy of a forest stand is required for a reliable assessment of the amount of forest combustible materials (FCM). The optimal combination of parameters for the correct classification of the number of undercanopy components while maintaining acceptable shooting performance is achieved with the following characteristics: UAV flight speed – 3 m/s, UAV flight height – 60 m, cross-over – 70%. With these parameters, the density of the point cloud under the canopy of the pine stand is about 144 pcs./m², which provides sufficient detail for the identification of the lower-tier components of the plantations. The practical significance of the work is to develop scientifically based recommendations for setting the parameters of lidar surveying for remote monitoring of forests in terms of determining the accumulation of LGM.