Comparison of conventional measurement and LiDAR-based measurement for crown structures

• Comparison of Conventional and LiDAR-based Measurement for Crown Structures.
• A LiDAR-based crown projection area calculating method was proposed.
• A LiDAR-based crown volume calculating method was proposed.
• Comparison of LiDAR-based crown projection and conventional projection.
• Comparison of LiDAR-based crown volume and conventional volume.

Tree crown projection area and crown volume are the important parameters for the estimation of biomass and other forestry science applications. However, it is difficult to validate their accuracy. In this research, measurement errors were quantified based on the 3D virtual LiDAR dataset of 22 common tree species in Beijing, China, which were derived from high-resolution terrestrial laser scanner. The hypotheses include that: (1) primary sources of height measurement are the violations of Total station based on the triangulation theory; (2) approximation of tree crown projections with 4-point fixed angles are not precise enough for irregular crown silhouettes; and (3) tree crown volumes obtained by conventional method with a taper’s formula (VC) are not corresponding to the need of accurate measurement. The relative accuracies derived from total station measurements between crown base height (BT) and tree height (HT) were compared. Meanwhile, different methods for tree crown projections and crown volumes were researched. The results show that the measurement errors of HT (RMSE = 4.56 m) is higher than that of BT (RMSE = 3.35 m), VC (RMSE = 45.0243 m3) is 8.03% on average smaller than VVC (RMSE = 48.56094 m3), A4 is 25.5% on average larger than AV. The deviations between filed investigation method and virtual 3D LiDAR data could be attributed to irregularity of the crowns’ silhouettes. Based on the results, we propose that: (1) the use of 8-point or 16-point projection with fixed angles to estimate crown projections and (2) different regular volume formula to simulate crown volume according to the tree crown shapes.

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