A Novel Approach to Characterizing Crown Vertical Profile Shapes Using Terrestrial Laser Scanning (TLS)

Abstract

Crown vertical profiles (CVP) play an essential role in stand biomass and forest fire prediction. Traditionally, due to measurement difficulties, CVP models developed based on a small number of individual trees are not convincing. Terrestrial laser scanning (TLS) provides new insights for researching trees’ CVPs. However, there is a limited understanding of the ability to accurately describe CVPs with TLS. In this study, we propose a new approach to automatically extract the crown radius (CR) at different heights and confirm the correctness and effectiveness of the proposed approach with field measurement data from 30 destructively harvested sample trees. We then applied the approach to extract the CR from 283 trees in 6 sample plots to develop a two-level nonlinear mixed-effects (NLME) model for the CVP. The results of the study showed that the average extraction accuracy of the CR when the proposed approach was applied was 90.12%, with differences in the extraction accuracies at different relative depths into the crown (RDINC) ranges. The TLS-based extracted CR strongly correlated with the field-measured CR, with an R2 of 0.93. Compared with the base model, the two-level NLME model has significantly improved the prediction accuracy, with Ra2 increasing by 13.8% and RMSE decreasing by 23.46%. All our research has demonstrated that TLS has great potential for accurately extracting CRs, which would provide a novel way to nondestructively measure the crown structure. Moreover, our research lays the foundation for the future development of CVP models using TLS at a regional scale.

Comparison of Three Approaches for Estimating Understory Biomass in Yanshan Mountains

“…As an active remote sensing approach, LiDAR (Light Detection and Ranging) allows accurate measurement of distances by transmitting laser pulses and analyzing the returned energy as a function of time [20], and it has emerged as a feasible tool for extracting crucial forest structure parameters [21]. Over the past two decades, LiDAR developed rapidly with multiple platforms, including satellite platforms (ICESat and GEDI, and spaceborne laser scanning, SLS), airborne platforms including manned aircraft and drones (airborne laser scanning, ALS), and ground platforms (terrestrial laser scanning, TLS), providing technical support for monitoring a wide range of forest dynamics changes [22]. Airborne laser scanning (ALS) is well-established in forestry research for characterizing three-dimensional variation in a tree canopy structure at plot or stand level [23] and has proven to be a highly accurate tool for assessing tree volume [24] and biomass [25] in forested stands.…”