Characterizing Low-Lying Coastal Upland Forests to Predict Future Landward Marsh Expansion

We conducted TLS scanning between July and September 2022 (during leaf-on conditions). For each plot, we performed single-scan positions using a RIEGL VZ-400i (RIEGL Laser Measurement Systems GmbH, Horn, Austria). The VZ-400i operates in the near infrared wavelength (1550 nanometers) with range distances up to 350 meters. The scanner was mounted on a tripod 1.3 meters above the ground and equipped with a tilt mount in order to obtain one upright and one titled scan (90° from the vertical). To create a single point cloud from the two scans, reflector targets were placed around the scanner prior to scanning. The reflectors remain in the exact same positions for both scans, and are used to compute a transformation matrix in the RIEGL RiSCAN Pro software which facilitates the co-registration and merging of the two-point clouds. Alignment of the scans was also further refined using the multi-station adjustment (MSA) module in RiSCAN Pro (Wilkes et al. 2017, Decuyper et al. 2018). The purpose of using the single scan positions from the TLS was to provide an objective representation of forest stand structure at fixed distances from the forest edge and was more time efficient compared to scanning multiple positions within a plot (Calders et al. 2014, Seidel et al. 2016, Meeussen et al. 2020).本研究于2022年7月至9月（植被叶片全覆盖期）开展地面激光扫描（Terrestrial Laser Scanning, TLS）。针对每个试验样地，我们采用奥地利霍恩市RIEGL激光测量系统有限公司生产的RIEGL VZ-400i型激光扫描仪设置单站扫描位置。该型号扫描仪工作于近红外波段（1550纳米），最大测距可达350米。扫描仪被安装在离地1.3米的三脚架上，并配备倾斜支架，以分别获取正射扫描（垂直于地面）与垂直方向呈90°的倾斜扫描数据。为将两次扫描得到的点云整合为单一点云数据集，我们在扫描前于扫描仪周边布设了反射靶标；两次扫描过程中反射靶标的位置保持完全固定，随后通过RIEGL RiSCAN Pro软件计算转换矩阵，以实现两点云的配准与合并。扫描配准的精度还可通过RiSCAN Pro软件中的多站调整（Multi-station Adjustment, MSA）模块进一步优化（Wilkes等，2017；Decuyper等，2018）。本次研究采用单站扫描方案，旨在客观呈现距林缘固定距离处的林分结构，且相较于在样地内布设多站扫描的方式，该方案具备更高的时间利用效率（Calders等，2014；Seidel等，2016；Meeussen等，2020）。