Forest stand height determination from low point density airborne laser scanning data in Roznava Forest enterprise zone (Slovakia)

Abstract

The presented paper discusses the potential of low point density airborne laser scanning (ALS) data for use in forestry management. Scanning was carried out in the Rožnava Forest enterprise zone, Slovakia, with a mean laser point density of 1 point per 3 m2. Data were processed in SCOP++ using the hierarchic robust filtering technique. Two DTMs were created from airborne laser scanning (ALS) and contour data and one DSM was created using ALS data. For forest stand height, two normalised DSMs (nDSMs) were created by subtraction of the DSM and DTM. The forest stand heights derived from these nDSMs and the application of maximum and mean zonal functions were compared with those contained in the current Forest Management Plan (FMP). The forest stand heights derived from these data and the application of maxima and mean zonal functions were compared with those contained in the current Forest management plan. The use of the mean function and the contour-derived DTM resulted in forest stand height being underestimated by approximately 3% for stands of densities 0.9 and 1.0, and overestimated by 6% for a stand density of 0.8. Overestimation was significantly greater for lower forest stand densities: 81% for a stand density of 0.0 and 37% for a density of 0.4, with other discrepancies ranging between 15 and 30%. Although low point density ALS should be used carefully in the determination of other forest stand parameters, this low-cost method makes it useful as a control tool for felling, measurement of disaster areas and the detection of gross errors in the FMP data. Through determination of forest stand height, tree felling in three forest stands was identified. Because of big differences between the determined forest stand height and the heights obtained from the FMP, tree felling was verified on orthoimages

Accuracy of Photogrammetric UAV-Based Point Clouds under Conditions of Partially-Open Forest Canopy

“…The horizontal RMSE varied from 1.21 m to 4.13 m and the vertical RMSE varied from 0.39 m to 1.16 m. In order to reach the terrain in a forest, the canopy must be partially open when using photogrammetry. This is the main limitation when comparing UAV SfM photogrammetry to LIDAR measurements, which are capable of reconstructing surfaces located under trees (e.g., [46][47][48]). Therefore, test plots with a differing degree of tree cover were used in the presented study to enable partial reconstruction of terrain.…”

Determining basic forest stand characteristics using airborne laser scanning in mixed forest stands of Central Europe

“…Photogrammetry methods have been applied to forest mapping for long time, and ground geodetic methods were used only in cases where details were not achievable from orthophotos (Zíhlavník & Scheer 2000). The main advantage of ALS lies in the 3D point cloud obtainable by laser impulses passing through tree crowns (Smreček & Danihelová 2013). The development of ALS started during the 1970s and 1980s, and suitable scanning methods were derived during the 1990s.…”

Compass Measurement – Still a Suitable Surveying Method in Specific Conditions

“…The technology of terrestrial and airborne laser scanning could complement or even substitute the use of the compass measurement for this type of tasks in the future, but there is still a need to resolve a UDK 550.380.84 number of technological and methodological problems (see e.g. Smreček, Danihelová 2013;Hackenberg et al 2014). Another option could be the indoor positioning systems (e.g.…”